Sponsored by - Sandia National Laboratories

SAND2011-6705P

SAN DIEGO MARRIOTT MARQUIS & MARINA HOTEL . OCTOBER 16-19 . SAN DIEGO, CALIFORNIA USA

mailto:[email protected]

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The premier forum for the dissemination, review, and discussion of papers on specific electrical energy storage applications and technologies.

Sponsored by:

• U.S. Department of Energy • Sandia National Laboratories • Electricity Storage Association

Co-sponsored by:

• A123 Systems • East Penn Manufacturing Co. Inc. • Kema • GS Battery, Inc. • NGK Insulators, Ltd. • Ashlawn Energy

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CONTENTS

INTRODUCTION ............................................................................................................. 9

AGENDA .......................................................................................................................... 13

SESSION 1 – Policy and Economics of Electrical Energy Storage (EES) Don't Forget That: Past, Present, and Future Philosophy for Energy Storage ........................21 The Impacts of Regulation, Policy, Advanced Technologies, and Market Dynamics on

the Deployment of Energy Storage Processes .....................................................................25 Evaluating Modular Distributed Electricity Resources for Utility Transmission and

Distribution Upgrade Defferal and Life Extension .............................................................27 SESSION 2 – Grid Applications of EES

Energy Storage Technology Research and Development Efforts in California ......................31 Grid-Supporting Battery Energy Storage Systems in the Low-Voltage Distribution Grid .....33 Enabling Renewable Energy Transmission – Advanced Lead Carbon Energy Storage

System for Transmission Utilization Improvement ............................................................37 Determining Storage Reserves for Regulating Solar Variability on the Electric Power

Grid ......................................................................................................................................41 Recent Applications of Sodium-Sulfur (NAS) Battery System in the United States and In

Japan ....................................................................................................................................43

SESSION 3 – UK Research – Innovative Technologies Techno-Economic Modelling of a Utility-Scale Redox Flow Battery System........................49 Substrates for the Positive Electrode Reaction in the Zinc-Cerium Redox Flow Battery .......53 The Development of Flow Batteries from Proof of Concept to Pilot Scale (and Beyond) .....57 Temperature Dependence of Key Performance Indicators for Aqueous Electrochemical

Capacitors Containing Nanostructured Birnessite Manganese Dioxide .............................61

Poster Session 1 A Battery Storage System for Distributed Demand Response in Rural Environments ...........71 The State/Federal Energy Storage Technology Advancement Partnership Project .................75 Applying Renewable Storage to the Commercial Environment ..............................................77 Recent U.S. Policy and Legal Implications for Energy Storage Vis-À-Vis RPS Mandates ...79 Use of Storage to Mitigate Frequency Variations in a Load Frequency Control Model .........83

SESSION 4 – EES Electrochemistry

Exploration and Practice of Energy Storage Technology in Shanghai ....................................87 Applying a Variety of Battery Chemistries for Energy Storage ..............................................89 MetlLs: A Family of Metal Ionic Liquids for Redox Flow Batteries .....................................91

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SESSION 5 – Emerging Energy Storage Technology Zinc/Air – A Low-Cost, Long-Life, and Safe Battery Technology .........................................97 The Aqueous Electrolyte Sodium Ion Battery: A Low-Cost Solution From Aquion

Energy .................................................................................................................................99 Thermal Energy Storage as an Enabling Technology for Renewable Energy .......................103 Advanced Electrochemical Storage RD&D at Pacific Northwest National Laboratory for

Renewable Integration and Grid Applications ..................................................................107

SESSION 6 – Power Electronics Battery Module Balancing with a Cascaded H-Bridge Multilevel Inverter ..........................113 A Power Electric Conditioner Using Electrochemical Capacitors to Improve Wind

Turbine Power Quality ......................................................................................................117 Degradation Mechanisms and Characterization Techniques in Silicon Carbide

MOSFETs at High-Temperature Operation ......................................................................121 Sanyo’s Smart Energy System with a 1.5-Megawatt Hour Lithium-Ion Battery and

1-Megawatt Photovoltaic Solar System ............................................................................125 Ultra-High Voltage Silicone Carbide Thyristors – Next-Generation Power Electronics

Building Blocks .................................................................................................................129

SESSION 7 – Modeling and Simulation of EES Widespread Deployment of Electric Storage in the Industrial and Manufacturing

Sectors ...............................................................................................................................135 Modeling of PV Plus Storage for Public Service Company of New Mexico’s Prosperity

Energy Storage Project ......................................................................................................137 Optimization Routine for Energy Storage Dispatch Scheduling in Grid-Connected,

Combined Photovoltaic-Storage Systems .........................................................................141 Numerical Analysis on the Temperature Distribution in the Molten Sodium-Sulfur

Battery Module ..................................................................................................................145

Poster Session 2 Hydrogen Energy Storage ......................................................................................................151 Silicon Nano-Scoop Anodes for High-Power Lithium-Ion Batteries ....................................153 Economic and Cost Modeling of the Repurposing of Electric Vehicle Batteries for

Stationary Storage Applications ........................................................................................155 Experimental Approach for Thermal Modeling of Sodium-Sulfur Battery Based on

Isothermal Chamber Test ..................................................................................................157 Preliminary Findings of National Renewable Energy Laboratory’s Electric Vehicle

Lithium-Ion Battery Secondary-Use Project .....................................................................161 Effects of Operating Parameters on the Single-Cell Performance of the Vanadium Redox

Flow Battery for Energy Storage .......................................................................................165

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SESSION 8 – Emerging EES Technologies A New Iron/Vanadium (Fe/V) Redox Flow Battery ..............................................................169 Lifetime of Vanadium Redox Flow Batteries ........................................................................173 Demonstration of Energy Storage Using a Breakthrough Redox Flow Battery

Technology ........................................................................................................................177

SESSION 9 – EES Demonstrations Commercialization of Silicon Carbide Power Modules for High-Performance Energy

Applications.......................................................................................................................181 Second-Generation Compressed Air Energy Storage Technology Meeting Renewable

Energy/Smart Grid Requirements .....................................................................................183 Systems Integration Strategies for the 10-kWh Redflow Zinc Bromine Battery Module .....185 Managing the State of Charge of Energy Storage Systems Used for Frequency

Regulation .........................................................................................................................187

SESSION 10 – EES Special Applications Why Aren’t We Building New Grid-Scale Energy Storage Projects? The Case for

Pumped Storage .................................................................................................................193 Energy Storage—A Cheaper, Faster, and Cleaner Alternative to Conventional Frequency

Regulation .........................................................................................................................195 Ultracapacitor Technology for Utility Applications ..............................................................197 UltrabatteryTM Storage Technology and Advanced Algorithms at the MW Scale ................199

SESSION 11 – Compressed Air Energy Storage (CAES) New York State Electric and Gas American Recovery and Reinvestment Act Advanced

Compressed Air Energy Storage Demonstration Plant – 2011 Status ..............................203 Iowa Stored Energy Park “Lessons From Iowa” ...................................................................205 Small-Scale Scalable Compressed Air Energy Storage System with Thermal

Management ......................................................................................................................207

Poster Session 3 Olivine and Titanium Oxide Based Lithium-Ion Battery System for Stationary Energy

Storage ...............................................................................................................................211 PG&E Compressed Air Energy Storage in California ...........................................................215 Characterization and Assessment of Novel Bulk Storage Technologies ...............................217 Compressed Air Energy Storage and Geographic Aggregation: Mutually Reinforcing

Strategies for Integrating Wind Power ..............................................................................221 Simulation and Optimization of A Flow Battery in an Area Regulation Application ...........223

DOE ESS PROGRAM SNL PUBLICATIONS .......................................................... 225

EESAT 2011 SPONSORS ............................................................................................. 249

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INTRODUCTION The U.S. Department of Energy (DOE), Sandia National Laboratories and the Electricity Storage Association are pleased to welcome you to EESAT 2011, the eighth biennial conference on Electrical Energy Storage Systems Applications and Technologies.

Progress in the application of electrical energy storage has accelerated considerably during the past two years. A Federal tax incentive proposal has been introduced in Congress, California has passed a storage-related mandate, and the Federal Energy Regulatory Commission is fielding a Notice of Proposed Rule Making. Various

Independent System Operators (ISOs) are already developing appropriate signals, tariffs, and market structures. Extensive storage deployment has occurred in Hawaii to help balance the extensive introduction of renewable generation. Multimillion dollar rate cases are being submitted to public utility commissions. Japan has just announced an incentive program for residential storage and China has ambitious plans for deploying Storage and smart-grid technology.

New storage technologies are being proposed and developed, such as the new lead-carbon batteries, innovative flow batteries, and improved lithium-ion batteries. The investment community is beginning to show considerable interest in this area. The newly created ARPA-E has offered a venue for support of potentially transformational new technologies. DOE’s Office of Basic Energy Sciences has created six new Frontier Energy Research Centers focusing on fundamental research on energy storage, and the Office of Electricity Energy Storage program has seen a substantial funding increase for its diversified program. Also noteworthy are several large loan guarantees for storage projects issued by the DOE, including two 20-MW frequency regulation facilities.

The American Recovery and Reinvestment Act (ARRA) of 2009 has provided sizable support for 16 selected projects funded with $185 million with a $585 million cost share. Projects range from compressed air and grid-scale battery systems for wind support to frequency regulation and distributed storage. The first of the ARRA projects, an integrated photovoltaic and storage using lead-carbon technology, was just commissioned in September 2011. During the next years, the program will see completion of a spate of projects an order of magnitude larger than previous storage facilities.

Noteworthy also are developments on the international scene, such as the creation of a new energy research institute focusing on storage in the Basque country, increasing interest in the European Community, and ambitious storage deployment in the countries of the Arab Gulf.

Following the successes of the first seven EESAT conferences, EESAT 2011 addresses a wide range of electrical energy technologies. Scheduled sessions for EESAT 2011 include Policy and Economics of Electrical Energy Storage (EES), Grid Applications of EES, UK Research on Innovative Technologies, Emerging Electrical Energy Storage Technologies, Power Electronics, and Compressed Air Energy Storage. Conference papers from EESAT 2011 will be electronically reproduced and made available to all attendees soon after the conclusion of the conference.

The EESAT Committee is grateful for your presence and encourages you to share your expertise through formal and informal discussion and interaction with your peers.

Dr. Imre Gyuk, Manager Energy Storage Program U.S. Department of Energy

Ross Guttromson, Manager Energy Storage and Transmission Analysis Sandia National Laboratories

Brad Roberts, Executive Director Power Quality Systems Director S&C Electric Company, Power Quality Products Division

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EESAT 2011 – Agenda

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AGENDA – EESAT 2011

Time Slot Title Presenters

and Posters

Activity

Sunday, October 16 4:30pm–6:00pm Registration 6:00pm–8:00pm Welcome Reception

Monday, October 17 (Plenary) 7:30am–8:30am Registration (all Day) and Continental Breakfast

8:30am–8:40am Conference Announcement (Dan Borneo) 8:40am–9:00am Welcome Address (Dr. Imre Gyuk) 9:00am–9:40am Keynote Speaker #1

9:40am–10:05am A Battery Storage System for Distributed Demand Response in Rural Environments

McCann, R. 3 min ea, x 6 poster session #1 review

The State/Federal Energy Storage Technology Advancement Partnership Project

Margolis, A.

Applying Renewable Storage to the Commercial Environment

Hires, J.

Recent US Policy and Legal Implications for Energy Storage vis-à-vis RPS Mandates

Hernández, J.

Use of Storage to Mitigate Frequency Variations in a Load Frequency Control Model

Lim, M.

10:05am–10:25am AM BREAK Poster Session #1 (remainder of day) SESSION 1 – Policy and Economics of Electrical Energy Storage (EES) 10:25am–10:40am Don't Forget That: Past, Present, and Future Philosophy

for Energy Storage Price, A.

10:40am–10:55am The Impacts of Regulation, Policy, and Advanced Technologies, and Market Dynamics on the Deployment of Energy Storage Processes

Miller, G.

10:55am–11:10am Evaluating Modular Distributed Electricity Resources for Utility Transmission and Distribution Upgrade Deferral and Life Extension

Eyer, J.

11:10am–11:30am Question & Answer Session 11:30am–12:30pm LUNCH BREAK

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and Posters

Activity

SESSION 2 – Grid Applications of EES 12:30pm–12:45pm Energy Storage Technology Research and Development

Efforts in California Bining, A.

12:45pm–1:00pm Grid-Supporting Battery Energy Storage Systems in the Low-Voltage Distribution Grid

Geth, F.

1:00pm–1:15pm Enabling Renewable Energy Transmission – Advanced Carbon Energy Storage System for Transmission Utilization Improvement

Anderson, J.

1:15pm–1:30pm Determining Storage Reserves for Regulating Solar Variability on the Electric Power Grid

Norris, B.

1:30pm–1:45pm Recent Applications of Sodium-Sulfur (NAS) Battery System in the United States and In Japan

Hatta, T.

1:45pm–2:00pm Question & Answer Session 2:00pm–2:20pm PM BREAK

SESSION 3 – UK Research – Innovative Technologies 2:20pm–2:35pm Techno-Economic Modelling of a Utility Scale Redox

Flow Battery System Roberts, E. P. L., and Scamman, D. P.

2:35pm–2:50pm Substrates for the Positive Electrode Reaction in the Zinc-Cerium Redox Flow Battery

Nikiforidis, G., Berlouis, L.E.A., Hall, D., and Hodgson, D.

2:50pm–3:05pm The Development of Flow Batteries from Proof of Concept to Pilot Scale (and Beyond)

Wills, Dr. R., Ponce de Leon, Dr. C., and Walsh, Prof. F.

3:05pm–3:20pm Temperature Dependence of Key Performance Indicators for Aqueous Electrochemical Capacitors Containing Nanostructured Birnessite Manganese Dioxide

Slade, R. C. T., and Roberts, A. J.

3:20pm–3:40pm Question & Answer Session 5:30pm–7:30pm NETWORKING ESA Evening Reception

Tuesday, October 18 (Plenary) 7:30am–8:30am Registration (all Day) and Continental Breakfast 8:30am– 8:35am Conference Announcement (Dan Borneo)

SESSION 4 – EES Electrochemistry 8:35am-8:50am Exploration and Practice of Energy Storage Technology

in Shanghai Yu, Z.

8:50am-9:05am Applying a Variety of Battery Chemistries for Energy Storage

Miller, T. or Roberts, B.

9:05am–9:20am MetILs: A Family of Metal Ionic Liquids for Redox Flow Batteries

Anderson, T.

9:20am–9:40am Question & Answer Session

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and Posters

Activity

9:40am–10:05am Hydrogen Energy Storage Wolf, E. 3 min ea. x 6 poster session #2 review Silicon Nano-Scoop Anodes for High-Power Lithium-Ion

Batteries Koratkar, N.

Economic and Cost Modeling of the Repurposing of Electric Vehicle Batteries for Stationary Storage Applications

Jaffe, S.

Experimental Approach for Thermal Modeling of Sodium-Sulfur Battery Based on Isothermal Chamber Test

Lee, C.

Preliminary Findings of National Renewable Energy Laboratory’s Electric Vehicle Lithium-Ion Battery Secondary-Use Project

Neubauer, J.

Effects of Operating Parameters on the Single-Cell Performance of the Vanadium Redox Flow Battery for Energy Storage

Wu, Chun-Hsing

10:05am–10:35am AM BREAK Poster Session #2 (remainder of day) SESSION 5 – Emerging Energy Storage Technology 10:35am–10:50am Zinc/Air – A Low-Cost, Long-Life, and Safe Battery

Technology Oster, M.

10:50am–11:05am The Aqueous Electrolyte Sodium Ion Battery: A Low-Cost Solution From Aquion Energy

Whitacre, J.

11:05am–11:20am Thermal Energy Storage as an Enabling Technology for Renewable Energy

Denholm, P.

11:20am–11:35am Advanced Electrochemical Storage RD&D at Pacific Northwest National Laboratory for Renewable Integration and Grid Applications

Yang, Z.


SESSION 6 – Power Electronics 1:00pm–1:15pm Battery Module Balancing with a Cascaded H-Bridge

Multilevel Inverter Sandberg, C., and Senesky, M.

1:15pm–1:30pm A Power Electronic Conditioner Using Electrochemical Capacitors to Improve Wind Turbine Power Quality

Crow, M.

1:30pm–1:45pm Degradation Mechanisms and Characterization Techniques in Silicon Carbide MOSFETs at High-Temperature Operation

Kaplar, R.

1:45pm–2:00pm Sanyo’s Smart Energy System with a 1.5-Megawatt Hour Lithium-Ion Battery and 1-Megawatt Photovoltaic Solar System

Hanafusa, H.

2:00pm–2:15pm Ultra-High-Voltage Silicon-Carbide (SiC) Thyristors–Next-Generation Power Electronics Building Blocks

Singh, R.


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and Posters

Activity

SESSION 7 – Modeling and Simulation of EES 3:00pm–3:15pm Widespread Deployment of Electric Storage in the

Industrial and Manufacturing Sectors Scalzo, P.

3:15pm–3:30pm Modeling of PV Plus Storage for Public Service Company of New Mexico's Prosperity Energy Storage Project

Lavrova, O.

3:30pm–3:45pm Optimization Routine for Energy Storage Dispatch Scheduling in Grid-Connected, Combined Photovoltaic-Storage Systems

Washom, B.

3:45pm–4:00pm Numerical Analysis on the Temperature Distribution in the Molten Sodium-Sulfur Battery Module

Min, J., and Hui-Lee, C.

4:00pm–4:20pm Question & Answer Session 5:30pm – 9:00pm NETWORKING Dinner Cruise

Wednesday, October 19 (Plenary) 7:30am–8:30am Registration (all Day) and Continental Breakfast 8:30am–8:35am Conference Announcement (Dan Borneo)

SESSION 8 – Emerging EES Technologies 8:35am–8:50am A New Fe/V Redox Flow Battery Li, L. 8:50am–9:05am Lifetime of Vanadium Redox Flow Batteries Schreiber, M. 9:05am–9:20am Demonstration of Energy Storage Using a Breakthrough

Redox Flow Battery Technology Horne, C.

9:20am–9:40am Question & Answer Session 9:40am–10:05am Olivine and Tantium Oxide Based Lithium-Ion Battery

System for Stationary Energy Storage Choi, D. 3 min ea. x 5 poster

session #3 review PG&E Compressed Air Energy Storage in California Narang, A. Characterization and Assessment of Novel Bulk Storage

Technologies Agrawal, P.

Compressed Air Energy Storage and Geographic Aggregation: Mutually Reinforcing Strategies for Integrating Wind Power

Succar, S.

Simulation and Optimization of a Flow Battery in an Area Regulation Application

Mellentine, J. A., and Savinell, R. F.

10:05am–10:30am AM BREAK Poster Session #3 (remainder of day)

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and Posters

Activity

SESSION 9 – EES Demonstrations 10:30am–10:45am Commercialization of Silicon Carbide Power Modules for

High-Performance Energy Applications Hornberger, J.

10:45am–11:00am Second-Generation Compressed Air Energy Storage Technology Meeting Renewable Energy/Smart Grid Requirements

Nakhamkin, M.

11:00am–11:15am Systems Integration Strategies for the 10-kWh Redflow Zinc Bromine Battery Module

Hickey, S.

11:15am–11:30am Managing the State of Charge of Energy Storage Systems Used for Frequency Regulation

Lazarewicz, M.


SESSION 10 – EES Special Applications 1:00pm–1:15pm Why Aren’t We Building New Grid-Scale Energy Storage

Projects? The Case for Pumped Storage Manwaring, M.

1:15pm–1:30pm Energy Storage—A Cheaper, Faster, and Cleaner Alternative to Conventional Frequency Regulation

Lin, J., and Damato, G.

1:30pm–1:45pm Ultracapacitor Technology for Utility Applications Burke, A. 1:45pm–2:00pm Ultrabattery Storage Technology and Advanced

Algorithms at the Megawatt Scale Coppin, P.


SESSION 11 – Compressed Air Energy Storage (CAES) 2:35pm–2:50pm New York State Electric and Gas American Recovery and

Reinvestment Act Advanced Compressed Air Energy Storage Demonstration Plant – 2011 Status

Rettberg, J., and Schainker, R.

2:50pm–3:05pm Iowa Stored Energy Park “Lessons From Iowa” Holst, K. 3:05pm–3:20pm Small-Scale Scalable Compressed Air Energy Storage

System with Thermal Management Simmons, J. H.

3:20pm–3:35pm Question & Answer Session 3:35pm–4:00pm Closing Remarks by ESA and Dr. Gyuk

SAND2011-5698P

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Session 1 – Policy and Economics of Electrical Energy Storage (EES)

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DON’T FORGET THAT: PAST, PRESENT, AND FUTURE PHILOSOPHY FOR ENERGY STORAGE

Anthony Price

Swanbarton Ltd., Malmesbury, United Kingdom

ABSTRACT Most of the deployment of large-scale electrical energy storage took place between 20 and 30 years ago under

different commercial and regulatory regimes. As pressure increases to access specific applications for electricity storage, it is appropriate to consider the role of storage in power system planning and the similarities between electricity storage and other storage processes.

Keywords: history, economics, practice

BACKGROUND

The purpose of electricity storage is to store electricity because it is better than producing it at the moment of delivery. The first sources of electricity were electrochemical; stored potential chemical energy was converted into a voltage and used for electroplating and, later, lighting. The advent of large-scale generators, and, later, alternators offered new paradigms in the method of operation of power networks.

EARLY DEPLOYMENT OF ELECTRICITY STORAGE

DC systems had an air of both simplicity and complexity. Simplicity, because accumulators could be used to provide a reserve of power. At first, some DC battery systems were used to provide a nighttime lighting supply, although some historical sources describe nighttime load (primarily for lighting) being supplemented by accumulators to meet the peak power requirement. Complexity, because of the need to provide very local services in order to avoid voltage loss and the lack of opportunities for changing voltage with transformers. The switch to AC systems and large interconnected networks led to large-scale storage, typically pumped hydro.

Many observers comment on the economic cycle, and how investment opportunities and expectations arrive in waves, fuelled by emotion and sometimes technology. The current wave of enthusiasm for energy storage technologies is now aligned closely to the development of green technologies, in contrast to the investment cycle of a

decade ago when alignment was closer to cost reduction and resilience against man-made attack or natural disasters. Before that, other reasons were prevalent for the deployment of electricity storage.

Investment in large-scale pumped hydro during the period 1960 to 1980 was driven by an interest in cost reduction for peaking plant against low costs of baseload plant. Centralized, often government-owned, integrated utilities, with a very low cost of capital and investment rates of return timed against 40-year payback periods were able to justify apparently expensive projects. Those utilities with nuclear power stations could gain additional benefits from pumped hydro as these storage plants could offer valuable nighttime load (which maintained the minimum must run capability) as well as services such as ramping, frequency and black start. The Electric Power Research Institute (EPRI) (among others) had an extensive energy storage program and both technical and economic research was ongoing.

During the 1980s. there was a near-universal decision to change from centrally planned and regulated utilities to a market-based, but no less regulated, industry structure, relying on new participants to construct low-cost generating capacity. This coincided with a decline, although not a withdrawal, in the construction of large-scale pumped hydro storage.

The slow start by battery storage developers in getting project commitment during the period 2000 to 2010 shows the variety of pressures that existed at that time. In marked contrast, the past two years have

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shown that alternative methodologies can bring substantial rewards. However, the recent successes are not because the rules have changed, but the externalities have been approached in a different way.

ECONOMICS AND ELECTRICITY STORAGE

The economic and commercial drivers for electrical energy storage can be summarized by comparing the storage of electricity to the storage of other goods and the use of other time-sensitive services, such as fresh bread, hotel rooms, or airline seats.

The economics of just-in-time manufacture depend on maintaining a constant throughput of raw materials and dispatch of the finished product. Stocks are typically held at the lowest levels, perhaps to avoid the financing cost. But while continuous 24-hour-day manufacturing may be possible in order to avoid underutilized manufacturing assets, there are few products that can be dispatched on a continuous basis. Even the main water supplies use storage at key parts of the system to act as buffers.

Like any other commercial asset, warehouses need to be financed, located, and used to maximum advantage if maximum economic value is to be obtained. In its simplest form, electricity storage may be considered as a warehouse for electricity and some simple laws of warehousing as applied to electrical storage can be expressed as follows:

(1) Storage should only be sited once on a power system [1]. Maximum benefit is gained from the store if the system is optimized for both technical and commercial efficiency. Usually this means that there should only be one store on a path between a generator and a consumer. More storage on the same path will decrease its value.

(2) Storage should be located as close to an end

consumer as possible [2]. The maximum benefits accrue from increased utilization of all the components of the system, generation, transmission, distribution, and supply. Counter to this argument is the issue of cost and size of the storage plant. As storage is moved closer to the consumer its specific cost will increase. There is therefore an optimum point of connection.

(3) The ownership of the store determines its

value [3]. If a consumer owns a store, it

indicates that the tariffs of the utility are less than optimum. If the store, in the same place as before, is owned by the utility it indicates that they are seeking to offer the lowest-cost tariffs to the consumer.

(4) Storage is a system benefit. Just as the early

developers of electricity sought to use storage to improve the efficiency of the whole system, the same is true in the modern context. Therefore maximum value is seen by a vertically integrated utility. Portfolio players usually obtain more value than sole operators of storage [4]. Following this thinking leads to the proposal that premium sites for electricity storage are frequently either geographical or electrical islands, which operate either as a vertically integrated utility or a proxy portfolio.

(5) Finally, storage is subjected to the rules of

warehousing: build the warehouse at the lowest cost; site it at the optimum point on the network; move the goods in and out fast; when it is worth buying stock, buy at the maximum rate; and, conversely, discharge at the maximum rate at the optimum price [5].

There are a number of extensions to these rules

that are very applicable to electricity storage. For example, the true cost of the warehouse includes the access roads, maintenance costs, property taxes, and the like. Warehouse security normally limits losses in transit, but electricity storage often has 20 or 25% “transit losses.” This loss, if repeated several times in the system by many electricity stores in series, would be devastating to the economics of electricity.

The effect of choosing the correct location can be significant. A warehouse (or buffer) in the supply chain for time-sensitive goods can advantageous to the utilization factor of the upstream supply chain. If it is essential to meet a continuously variable demand, using high-asset-value production equipment, it is more economically viable to use the production equipment operating at average demand and use the buffer to meet the peaks, but only if the asset and operating cost of the production plant is less than the asset and operating cost of the store. This is a fundamental point, and should be an integral part of the electricity arbitrage models as they are frequently used to model storage. But the equally important point is that if the storage plant is also operated by either the producer or the supply company, then a whole system benefit can also be

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achieved. When this axiom is acknowledged it becomes possible to use storage as a means of optimizing the whole system by reducing the total system operating costs. This point is significant in the consideration of integrating electricity storage with renewable generation.

In a commercial electricity supply system, which is operated for the public good, it would be logical if the energy storage system was placed as close to the end consumer as possible and owned and operated by the utility company, and the resulting savings passed onto the consumers as a whole.

THE PRESENT Substantial progress in the past two years has

been achieved, mainly through the deployment of demonstration projects, but in most cases by focusing on a specific niche application that exploits the value-added nature of one of these rules. While initially the system benefit is seen to the main driver for electricity storage, the value creation for the owner of storage arises from the ability to move the stock in and out of the warehouse as fast and as efficiently as possible – or to use the ability to change the continuous supply of electricity into a variable supply by providing fast-acting upwards and downwards reserves and frequency controls.

REFERENCES [1] K. Nix, National Power PLC, referenced in Electric Power Research Institute workshop on electricity storage, 1995.

[2] N. Rigby, ibid.

[3] K. Kramer, Bewag AG, verbal communication, 5th International Batteries Conference, Berlin, 1993.

[4] P. Johnson, National Power PLC, ibid.

[5] A. Price, National Power PLC, Proceedings of EESAT 2000, 2000.

BIOGRAPHICAL NOTE Conference presenter: Anthony Price established Swanbarton as a consultancy business specializing in electrical energy storage in 2003 and has since consulted for battery and energy storage developers, users of storage, utilities, and government

departments, in the United Kingdom (UK) and overseas. He is interested in the commercial aspects of all types of energy storage, market acceptability, and commercial development and has had many papers and journal articles published on these subjects. He is a contributor to Escovale’s management report on flow batteries and has written a number of published papers and journal articles, particularly on electricity storage. He served as a director of the European Space Agency (ESA) for seven years and has organized a number of meetings for the ESA in Europe, and is now the Director of the Electricity Storage Network, the industry body for electricity storage in the UK. In 2010, he initiated the International Flow Battery Forum, a conference series that brings together researchers, developers, and users of flow batteries.

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THE IMPACTS OF REGULATION, POLICY, ADVANCED TECHNOLOGIES, AND MARKET DYNAMICS ON THE DEPLOYMENT OF ENERGY

STORAGE PROCESSES

Gabriel Miller1 and Garth Corey2 1Hudson Clean Energy Partners, Teaneck, New Jersey, USA

2Consultant, Albuquerque, New Mexico, USA

Keywords: advanced technologies, regulatory initiatives, markets

A number of factors are now coalescing that can

be expected to lead to significant market opportunities for energy storage in the near term. These include, but are not limited to, government policy and regulatory initiatives; new requirements in wholesale electric markets, particularly related to the transmission and distribution of power; an increase in the percentage of intermittent power sources available (especially in certain regions of the United States) leading to more significant requirements associated with, for example, frequency and voltage control; new larger megawatt-hour systems that can be utilized for dispatch during peak periods; the increased utilization of distributed energy systems; the impact of electric vehicle storage and the charging impact on the grid; and the possible integration of storage into smart grid platforms.

As the U.S. energy delivery system adapts to meet changes in supply and demand patterns; changes in policy, as well as new and proposed regulations; requirements for increased efficiency; and capital and market constraints, it appears that energy storage can play an increasingly significant role. This paper focuses on each of the factors listed above and discusses how available and emerging technologies will impact each. The paper examines impacts associated with advanced battery systems, compressed air energy storage, pumped hydro, flywheels, and ultra-capacitors. With respect to battery storage, technologies such as advanced lead-acid, sodium sulfur, lithium-ion, and flow batteries are examined in detail, and technologies that should be favored, in the near term, for specific applications are identified. In addition, the possibility and plausibility of “stacking” applications for specific technologies is addressed.

With respect to utility-scale energy storage systems, a new and compelling interest has

been emerging. Many applications, from substation and transmission upgrade deferral for utility-scale applications to distributed energy storage for community-scale applications, have now been identified that are best solved by energy storage solutions of a duration of 4 or more hours. However, near-term focus by system developers for energy storage applications has been on power applications, those applications requiring megawatt (MW)-scale power for only short periods of time, typically 15 to 45 minutes. Although there is significant interest in bulk energy storage for applications requiring MW-scale power for 4 or more hours, currently there is only one turnkey system in the market that can deliver on this requirement, and this supplier is backlogged for the next several years in filling current orders. Consequently, opportunity exists for new players in the bulk energy storage world.

What is really needed to continue the enabling of energy storage in the bulk storage arena are changes in regulatory policies and directives as they define generation, transmission, and distribution assets. This would occur by broadening the definition of what types of devices are included in each category. These changes in policy can lead to new rules and directives that define tariffs for the purchase of these services by the appropriate energy managers, including Independent Power Producers and the major Independent System Operators and Regional Transmission Organizations throughout the system. These changes could then direct downward to local utilities (rural and municipalities) that desire to employ bulk energy storage systems in their operations, but currently have no way to recover the cost of deploying these technologies. The definition of these new terms and conditions, in turn, would provide the necessary motivation to the bulk storage systems developers to make the appropriate financial and technical commitment to bring cost-effective

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bulk storage turnkey solutions to the market. This would lead to a truly effective Smart Grid.

With respect to the aforementioned regulatory and policy initiatives necessary to spur the growth of storage utilization, both domestically and internationally, such regulation and policy initiatives continue to evolve. The paper examines federal and state initiatives, as well as initiatives abroad. With respect to the federal regulatory initiatives, the Federal Energy Regulatory Commission (FERC) has one regulation recently put into effect (FERC Order 1000), as well as Notices to Proposed Rulemaking (NOPRs) and Notices of Inquiry (NOIs), which can be expected to ultimately drive growth in the U.S. market. With respect to state initiatives, California regulations (including AB 2514) have made California by far the leading market for storage in the United States. With respect to China, storage is specifically mentioned in the 12th Five-Year Plan as an important technological development in clean energy ( primarily electric vehicle [EV]) applications. However, State Grid is conducting various test programs for different storage technologies as a precursor to policy design. The implications of the evolving policy and regulatory landscape, nationally and internationally, are addressed.

BIOGRAPHICAL NOTES Conference presenter: Gabriel Miller, Ph.D., Chief Scientific Officer of Hudson, is responsible for technical analysis of clean technologies at Hudson. Dr. Miller is a retired Professor of Chemistry at New York University (NYU) and previously was a Professor of Engineering as

well as a Professor of Energy and Atmospheric Science at NYU. Dr. Miller has conducted numerous studies at NYU and in a number of energy and environmental fields as a consultant. In the 1980s, he headed research programs in a number of renewable energy fields that have recently regained importance.

His work addressed a variety of combustion systems, including studies of human exposure to toxic emissions from municipal solid waste facilities, and analyses of power plant systems for compliance with the Clean Air Act Amendments of 1990. Dr. Miller has led projects in boiler design, gas and oil-fired cogeneration, hydrolysis of waste to glucose, municipal solid waste and sludge incineration, biofuel combustion, coal and wood waste fired fluidized bed combustion, wind energy, hydropower, power transmission by microwaves, wastewater system requirements, and air and odor impacts for health risk analyses. He also managed production of engineering feasibility studies, as part of due diligence for bond issues, as well as compliance with the Clean Air Act Amendments of 1990. Dr. Miller serves as Executive Director of the Society for Energy and Environmental Research (SEER), where he oversees studies in bio-fuel production. He earned a B.S. degree, M.S. degree and Ph.D. in Aerospace Engineering from NYU.

Garth P. Corey, Consultant to Hudson, recently retired as a Principal Member of the Technical Staff of Sandia National Laboratories (SNL), and had project management responsibilities with the Energy Infrastructure and Distributed Energy Resources

Department. Throughout his SNL career, he was involved in high-technology energy storage research and development and demonstration projects. He is a member of the IEEE Power and Energy Society and active with the PES Stationary Battery Committee. In addition to continuing his association with SNL as a consultant with responsibilities related to electric energy storage systems, he remains active in a consulting role to the energy storage industry in the evaluation of emerging energy storage technologies and systems for bulk storage and distributed energy storage applications on the national grid.

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EVALUATING MODULAR DISTRIBUTED ELECTRICITY RESOURCES FOR UTILITY TRANSMISSION AND DISTRIBUTION UPGRADE

DEFERRAL AND LIFE EXTENSION

James M. Eyer

Distributed Utility Associates, Inc., Oakland, CA, USA

ABSTRACT This paper documents an investigation, sponsored by the U.S. Department of Energy, of the prospects for

modular electricity storage used to defer expensive upgrades to electric utility transmission and distribution facilities or to extend the useful life of existing equipment. Resulting benefits could provide the basis for attractive distributed energy resources value propositions, especially for distributed generation and distributed storage.

INTRODUCTION

Transmission and distribution (T&D) deferral involves use of small distributed energy resources (DERs), located electrically downstream from heavily loaded elements of the T&D system (hot spots) to either (1) delay the need to undertake an expensive upgrade of existing T&D equipment (deferral) or (2) extend the useful life of existing T&D equipment (life extension). In both cases, a relatively small amount of DER capacity is added “on the margin” to serve a portion of peak load during the few days per year when customer demand is highest. When used for T&D upgrade deferral, the DER serves the portion of total peak demand that would otherwise exceed the load-carrying capacity of the T&D equipment. In the case of T&D life extension, the DER reduces loading-on the T&D equipment, which reduces equipment wear, heating, and ground faults.

WHY DERs FOR T&D UPGRADE DEFERRAL AND LIFE EXTENSION

ARE IMPORTANT DERs will be an important and possibly

significant element for the electricity grid and marketplace of the future for a variety of reasons.

Key elements of the DER value proposition include financial and societal benefits related to (a) lower overall cost-of-electric service, (b) more flexible utility capacity expansion approaches, (c) more optimal electric service reliability and power quality, (d) increased energy efficiency, (e) fuel diversity, and (f) variable renewable generation integration.

DERs used for T&D deferral or life extension could allow utilities to serve customer energy and power needs at lower cost, with more reliability, more efficiency, and with lower and fewer land and environmental impacts than is possible using standard capacity expansion approaches involving central generation plus conventional T&D equipment (primarily T&D wires and transformers and capacitors).

Due to the significant potential financial benefit, use of DERs for T&D deferral/life extension will be a key anchor benefit for a variety of DER value propositions (i.e., benefit combinations).

KEY INDICATORS Using DER to provide capacity on the margin is

not always a viable option. In many cases, the lowest-cost alternative is a conventional grid buildout. In other cases, there may already be as much DER capacity as is technically viable, or in the case of distributed generation (DG), the necessary fuel infrastructure for operating may not exist.

Criteria that indicate modular electricity storage (MES) might be viable for T&D deferral or life extension include (a) high T&D cost, (b) high peak-to-average demand ratio, (c) modest projected overload, (d) slow peak demand growth (rate), (e) uncertainty about the timing and/or likelihood of block load additions, (f) T&D construction delays or construction resource constraints that may be a challenge, (g) the T&D upgrade project competes with other important projects for capital, and (h) the same MES provides additional benefits – revenue or

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avoided cost – that can be aggregated into an attractive total value proposition, such as on-peak energy and electric supply capacity. MES is especially well suited to those locations if air emissions regulations, noise regulations, fuel storage, or other safety-related challenges restrict use of combustion-based DG and if the price differential is large between times when storage is charged and when it is discharged.

BENEFIT ESTIMATION FRAMEWORK

The investigation included development of a generalized framework for estimating the financial benefit of deferring a T&D upgrade for one year.

Two key criteria are (1) T&D equipment cost per kilowatt (kW) installed, and (2) the amount of MES capacity needed (storage portion). Benefit values for various combinations of those two criteria are shown in Figure 1. Those benefits are based on representative values for two other important criteria: (1) an “upgrade factor” and (2) a “fixed charge rate.” The upgrade factor is the amount of T&D load-carrying capacity to be added – 0.33 is used (for a 33% increase). The annual fixed charge rate for utility capital plant is assumed to be 11% of installed cost per year).

0

400

800

1,200

1,600

2,000

75 100 125 150 175 200 225 250T&D Cost ($/kW installed)

Ben

efit

($/k

W S

tora

ge, f

or o

ne y

ear)

1.0%2.0%3.0%4.0%6.0%8.0%

Fixed Charge Rate = 0.11 T&D Upgrade Factor = 0.33

*Storage pow er relative to the EXISTING T&D equipment's rated capacity.

Storage Power*

Fig. 1. Benefit values.

Per the figure, if DER capacity equal to 4% of the T&D equipment’s load-carrying capacity (labeled as storage power in the figure) can be used to defer a relatively expensive T&D upgrade with an installed cost of $125/kW (as shown on the X-axis), then the single-year deferral benefit is about $480/kW of DER capacity. That is the benefit for one year of deferral. If deferrals or life extensions are multiyear, then the benefits for each year are additive.

CONCLUSION There are hundreds of milliwatts/year for which

the T&D deferral/life extension benefit (a) is significant (hundreds of dollars per kW-year) and (b) may be combined with benefits from several other compatible uses, to comprise an attractive value proposition.

BIOGRAPHICAL NOTE Conference presenter: Jim Eyer is the Principal and Senior Analyst for E&I Consulting. For the last 15 years, he has also served as the Senior Analyst for Distributed Utility Associates.

Mr. Eyer’s 27-year career has focused on energy efficiency, renewables, and advanced energy technologies, concepts, benefits, and markets. For the last 15 years, he has focused on energy storage with an emphasis on benefits and value propositions. He has authored or co-authored numerous reports and papers on these subjects for the U.S. Department of Energy, California and New York State energy agencies, utilities, and vendors. Notably, he is the lead author and principal investigator for the seminal report published by Sandia National Laboratories entitled Energy Storage for the Electricity Grid: Benefits and Market Potential Assessment Guide.

Before Distributed Utility Associates, Mr. Eyer held a range of positions with Pacific Gas and Electric Company related to advanced electric technology and concepts research and development, electric supply planning, and commercial energy efficiency services.

He holds an undergraduate degree in physics and management from Sonoma State University and a Master’s degree in management, also from Sonoma State.

Session 2 – Grid Applications of EES

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ENERGY STORAGE TECHNOLOGY RESEARCH AND DEVELOPMENT EFFORTS IN CALIFORNIA

Avtar Bining, Ph.D.

California Energy Commission

In less than a decade, small-scale energy storage

technologies (e.g., batteries) have become a critical and vital component for the reliable performance of handheld devices (e.g., cell phones and “BlackBerrys”) used for communications and information processing in the world. As rapid advances in communication and information processing technologies and their more-than-ever sought-after role in transforming the electric power grid becoming apparent, energy storage technologies will play a major role in making it a reality for a reliable, secure, sustainable, and efficient electric power grid (i.e., “smart grid”) capable of dealing with massive changes worldwide over the next few decades. Therefore, it is absolutely imperative and critical that energy storage technologies be appropriately developed and deployed to facilitate the electricity delivery system transformation and support the growth and deployment of smart grid as well as renewable energy resources. Energy storage technologies can provide many benefits such as

improved grid optimization for bulk power production, balanced power system despite variable or diurnal or intermittent renewable energy sources, integration of plug-in hybrid electric vehicle (PHEV) power demands with the electric power grid (presumably smart grid), enabling the deployment of renewable energy resources, reducing and/or eliminating or deferring investments in transmission and distribution (T&D) infrastructure to meet peak loads (especially during outage conditions), enhanced usage of the existing T&D infrastructure, reducing greenhouse gas emissions and climate change impacts, and providing ancillary services directly to grid/market operators. This presentation provides a glimpse of the basic and applied research efforts under way in California on energy storage technology and its various applications for electricity T&D as well as electric-drive vehicles and other stationary applications, and potential for energy storage technology deployment in the coming years in California.

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GRID-SUPPORTING BATTERY ENERGY STORAGE SYSTEMS

IN THE LOW-VOLTAGE DISTRIBUTION GRID

Frederik Geth,1 Peter Tant,1 Daan Six,2 and Johan Driesen1

1Katholieke Universiteit Leuven, Leuven, Belgium 2VITO, Mol, Belgium

ABSTRACT

The integration of renewable energy sources into the distribution grid may cause more profound voltage deviations and overloading of grid elements. In certain countries (for example, Belgium), a lot of photovoltaic systems are connected to the low-voltage distribution grid at household residences. These renewable energy sources may cause excessive voltage increase at times when also the load is low (for example, during a weekday in summer). If the voltage increases above a certain limit, the photovoltaic systems are forced to stop injecting the energy into the grid. Battery energy storage systems can be installed to solve such a problem. Furthermore, battery energy storage systems can be applied for other goals throughout the grid; for example, electricity cost optimization and peak shaving at the household, feeder, or transformer level. Control systems for providing such services are developed in a multilayered approach: from real-time control of the semiconductor components switching to the long-term optimization in grid planning.

Keywords: battery energy storage system, distribution grid, peak shaving, grid service

INTRODUCTION

Background

Low-voltage distribution grids are, in many places, suffering from increased loading since their inception, typically decades ago. The integration of local distributed generation offsets some of this load during certain periods of time, but it may also increase the occurrence of excessive voltage deviations at other moments, e.g., in low load situations.

Controlled intelligently, grid-coupled energy storage can be beneficial to multiple stakeholders in the electricity system [1]. If the storage efficiency and lifetime are sufficiently high, effective electricity costs for a Battery Electric Storage System (BESS) owner are lowered by charging when electricity cost is low and re-injecting when prices are high.

BESSs are expensive in terms of the investment in storage capacity. In practice, optimization methods are applied to achieve the most economic solution, whether it is for immediate benefits (e.g., through arbitrage on an electricity market), or longer-term benefits (e.g., avoiding grid investment). The outcome

of such optimization is a charge and discharge schedule for the BESS.

Control Loops and Layers

The distribution grid contains a variety of control loops on different timescales. In this subsection, different control layers are clarified to facilitate the discussion in the full paper on the optimality of the grid services. Table 1 gives a schematic representation of the discussion in the coming paragraphs.

Grid planning studies take into account the ever-changing nature of the loads and distributed energy resources to make assertions about, amongst others, the future optimal configuration and strengthening of the grid. This information is then used – feedback in the control loop – to decide what changes to make and when to make them.

On an operational timescale other things are controlled. Off-load tap changers may be manually adapted once a year. This allows for the compensation of long-term voltage decrease because of increased loading of the grid. Also, in some grids, the connection of the feeder parts with each other or with

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the transformer can be reconfigured, something which is usually done to reassure security of supply in case some grid component fails.

Electricity costs on a wholesale market have a certain time resolution; for example, for the Belpex in Belgium this is one hour [2]. Any device that takes pricing into account in its behavior will have a corresponding control strategy at this timescale.

Devices that are bidirectionally coupled to the grid through power electronics have a control system that determines the switching of the semi-conductor components, which may happen at frequencies on the order of 10 kilohertz. Through this switching, current waveforms at the ms scale are generated to coincide with those of the grid.

Table 1. Distribution grid timescales and control loops. timescale control loop decade Grid strengthening year Off-load tap change

Replacement of a transformer Feeder reconfiguration

day Charging/discharging schedule of BESS hour Electricity cost

On-load tap change ms Grid coupling by PV system or BESS μs Switching components

When a BESS is, for example, applied for voltage support, the distribution system operator (DSO) may avoid in the medium to short term the costly replacement of underground cables, as determined by a grid-planning study. Because of the relatively high cost of a BESS and to avoid over-investment, applying optimal siting and sizing methodology for the different objectives is crucial for a viable grid integration of the BESS [3]. A charging and discharging schedule for voltage support is determined in a window of days/weeks, but periodic modifications can take into account new information. In this BESS, grid-coupling paradigms with voltage and/or frequency droop, e.g., developed in Reference 4, are applied to facilitate local-scale and large-scale power system integration. Ultimately, it is only the physical switching of the semiconductor components that allows the current to flow from the battery to the grid and back.

OPERATIONAL CONSTRAINTS AND OBJECTIVES

A distinction is made between technical and economical objectives. An example of an economical objective for a BESS is electricity cost minimization, which corresponds with the well-known “buy low, sell high” strategy, also known as arbitrage. The pursuit of a technical objective offers benefits that may or may not be quantified as easily. If a household sometimes notices overvoltage problems and its photovoltaic (PV) system disconnects from the grid, the energy that could have been produced is wasted. This energy could then have been stored at that time and used later. However, for example, consider a DSO. The EN 50160 norm [5], applicable in Belgium, for voltage deviations in low-voltage grids dictates that for 95% of the week, deviations have to be within +/-10% of the nominal value. The DSO could install a BESS in a grid if more problems are detected than what is acceptable. The benefit now is that other grid-improving investments can be postponed.

A model is used to provide energy services at the lowest cost [6]; see Table 2 for the schematic overview. Technical constraints of the system are boundary conditions for the optimization for the energy service objective. Batteries have a certain storage capacity, storage efficiency, self-discharge, cycle life, shelf life, and charge and discharge rates. The power electronic interface to the grid has a certain efficiency, lifetime, and power rating. These parameters also determine the depreciation cost of cycling the battery.

The costs of owning and operating the BESS are determined by an economic cost model [7]. The total cost is determined as the sum of the fixed and the variable costs. The cost deprecation component is taken into account in the variable costs, as it depends on the operation of the system. Maintenance, investment, and the depreciation of the power electronics are taken into account in the fixed costs.

Table 2. BESS operation. BESS Operation

Technical constraints

Economic cost model

Energy service objective

Battery Power electronics

Fixed Variable Technical Economical Peak

shaving Voltage support

Arbitrage

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BESS DEVELOPMENT A 4.3-kilowatt hour grid-coupled BESS for peak

shaving application is developed. The BESS consists of an inverter, offering AC/DC and DC/DC conversion, and two battery modules in series, each composed of 48 lithium iron phosphate (LiFePO4) cells with a capacity of 15 Ah. These modules are each actively balanced and contain temperature sensors and per cell voltage measurement for computer readout (RS232). A battery protection module (BPM) checks the voltages and temperatures autonomously and signals if problems are detected. A programmable logic controller can open a circuit breaker, isolating the batteries, if necessary conditions are met. The programmable inverter is controlled in real time from the Matlab/Simulink environment.

The BPM avoids damaging the batteries during development; however, in normal operation it will not arrive in a fault situation because the boundary conditions are implemented redundantly in the Simulink control scheme. A rule-based control scheme avoids exceeding voltage, current, and state-of-charge limits of the battery [8]. A multistage constant current charging algorithm is implemented, because of its lifetime maximizing property [9]. The final control layer implements peak shaving. In the full paper, the performance of the BESS will be detailed. The application of peak shaving, with both positive and negative power limits, will be demonstrated in a case with residential load and PV generation and compared with a benchmark optimization.

REFERENCES [1] Bottling Electricity: Storage as a Strategic Tool for Managing Variability and Capacity Concerns in the Modern Grid, A Report of the Electricity Advisory Committee, December 2008.

[2] Belpex, www.belpex.be.

[3] F. Geth, J. Tant, E. Haesen, J. Driesen., and R. Belmans, “Integration of Energy Storage in Distribution Grids,” Power and Energy Society General Meeting, 2010, IEEE Vol. 2010, Issue 25-29, July 2010.

[4] T. Loix, K. De Brabandere, J. Driesen, and R. Belmans, “A Three-Phase Voltage and Frequency Droop Control Scheme for Parallel Inverters,” IECON 2007 - 33rd Annual Conference of the IEEE Industrial Electronics Society, no. 1, 2007, pp. 1662-1667.

[5] EN 50160, Voltage Characteristics of Electricity Supplied by Public Distribution Systems, 1999.

[6] F. Geth, J. Tant, T. De Rybel, P. Tant, D. Six, and J. Driesen, “Techno-Economical and Life Expectancy Modeling of Battery Energy Storage Systems,” in 21st International Conference and Exhibition on Electricity Distribution, 2011, Vol. 80, no. 1106.

[7] K.-H. Ahlert, “Economics of Distributed Storage Systems,” Karlsruher Institut Für Technologie, 2010.

[8] S. Teleke, M.E. Baran, S. Bhattacharya, and A.Q. Huang, “Rule-Based Control of Battery Energy Storage for Dispatching Intermittent Renewable Sources,” IEEE Transactions on Sustainable Energy, Vol. 1, no. 3, 2010, pp. 117-124.

[9] Yi-Hwa Liu and Yi-Feng Luo, “Search for an Optimal Rapid-Charging Pattern for Li-Ion Batteries Using the Taguchi Approach,” IEEE Transactions on Industrial Electronics, Vol. 57, no. 12, 2010, pp. 3963-3971.

BIOGRAPHICAL NOTE Conference presenter: Frederik Geth received the M.Sc. degree in electrical engineering from the Katholieke Universiteit Leuven (K.U.Leuven), Leuven, Belgium, in 2009. Currently, he is working as a research assistant with the division ESAT-ELECTA. His research interests include optimal

storage integration in distribution grids, batteries for (hybrid) electrical vehicles, and mitigating the impact of the charging of (hybrid) electrical vehicles on the low-voltage distribution grid.

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37

ENABLING RENEWABLE ENERGY TRANSMISSION – ADVANCED LEAD CARBON ENERGY STORAGE SYSTEM FOR TRANSMISSION UTILIZATION IMPROVEMENT

Jon Anderson, Stephen Mraz, and Daniel Boyer

C&D Technologies Inc., Blue Bell, PA, USA

ABSTRACT Advanced Lead Carbon Energy Storage Systems (ALCESS) are particularly well suited for increasing

renewable energy transmission in the electric grid. In general, congestion on the grid limits the flow of low marginal cost renewable generation to load. Reducing congestion at transmission bottlenecks is the most effective way of improving flows of low-cost renewable generation to urban areas. In this application, the ALCESS is located at a congestion point to provide back-up energy storage during a contingency event, thereby allowing the congestion point’s post-contingent limit to be increased by the capacity of the energy storage system. While the ALCESS is only deployed periodically, during a contingency, it allows the system operators to utilize a greater fraction of the congestion point’s transmission capacity – thereby reducing congestion at that location and facilitating the flow of low marginal cost renewable generation.

Keywords: energy storage, advanced lead carbon, VRLA, transmission utilization

INTRODUCTION

The traditional role of lead-acid batteries in stationary applications has been primarily to provide backup power and, depending on location, power conditioning. In a typical application, the actual use (discharge) of the battery is fairly infrequent and it remains on float charge for the majority of its service life.

However, the use of energy storage in large grid-scale systems is more similar to some cycling applications with repeated charge/discharge operation. In these applications, the traditional standby technologies perform poorly compared to other energy storage systems. Even lead-acid batteries designed for cycling applications do not perform as well as alternative technologies without sizing the systems to such an extent or reducing the expected service life to such a level that the primary advantage, cost, almost reaches parity with other solutions.

With the development of lead carbon technology for commercial products, many of the performance limitations of traditional lead-acid systems have been reduced or eliminated. The ability of lead carbon batteries to operate in a partial state of charge (PSoC) and the stabilizing effect the technology has on the electrodes in cycling without increasing cost has

increased the application possibilities for these systems.

Advanced Lead Carbon Energy Storage Systems (ALCESS) are particularly well suited for increasing renewable energy transmission in the electric grid. In general, congestion on the grid limits the flow of low marginal cost renewable generation to load. Reducing congestion at transmission bottlenecks is the most effective way of improving flows of low-cost renewable generation to urban areas.

In this application, the ALCESS is located at a congestion point to provide backup energy storage during a contingency event, thereby allowing the congestion point’s post-contingent limit to be increased by the capacity of the energy storage system. While the ALCESS is only deployed periodically, during a contingency, it allows the system operators to utilize a greater fraction of the congestion point’s transmission capacity – thereby reducing congestion at that location and facilitating the flow of low marginal cost renewable generation. The system can also provide contingent reserve power, peak price sales, and other market functions to further offset the capital cost of the system.

The main performance benefits of an ALCESS in this application are low relative cost, scalability, system mobility, and reliability, in terms of service

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life as a significant portion of the system is based upon mature technology.

LEAD CARBON TECHNOLOGY In a typical standby power application, the

primary failure mode is the degradation of the positive electrode due to corrosion. However, in the applications described in this proposal, with the additional requirements of high cycle life, possibly at temperature, and PSoC operation, the primary failure mode is found in the negative electrode.

Current state-of–the-art valve-regulated lead-acid (VRLA) negative electrodes utilize a number of additives to improve the performance and longevity of the cell [1]. Lignosulfonates are added to maintain the high surface area of the Negative Active Material (NAM) to improve utilization; barium sulfate is added to provide nucleation sites for the reaction product, lead (II) sulfate (PbSO4), preventing large crystals from forming. Large crystals with a limited surface area are difficult to convert back to lead on charge. Finally, carbon black is added to increase conductivity of the plate to improve charge acceptance. While other additives can and are used within the industry, these three constitute the overwhelming majority of additives.

In an application as presented here, the current electrode design would provide very good initial performance, but degrade very rapidly as the system continued to operate. The reasons and mechanisms for this are very well understood. In a PSoC, operation the negative electrode is held a various states of charge with a percentage of the active material converted to PbSO4. This PbSO4 can re-crystallize over time and converts to what is commonly referred to as “hard sulfate” [1]. In turn, these crystals become sites for preferential crystal growth. The resulting sulfate crystals are difficult to convert back into lead on recharge and a steady decrease in available capacity results over time as more and more PbSO4 is formed. In addition to suffering from sulfation in a PSoC operation, the negative electrode also limits charge acceptance of the cell. In a pulse charge operation, the majority of the current is converted to hydrogen evolution. This leads to dry out of the cell and also reduces the capacity over time.

Pavlov et al. [2] have demonstrated that the addition of electrochemically activated carbon (EAC) to the NAM can increase PSoC operation in high-rate applications by an order of magnitude, from 1000 micro-cycles to over 10,000 cycles. Mosely et al. [3] summarize the possible functions of the carbon additives in PSoC cycling.

(1) Electronic conductivity – The carbon particles maintain the conductivity of the active material in the presence of increased amounts of PbSO4, which are electrically insulating. These conductive pathways then facilitate charging despite the increased resistance of the plates.

(2) Restriction of crystal growth – Carbon prevents the progressive growth of PbSO4 crystals, maintaining surface area and improving charging characteristics [4].

(3) Hydrogen over potential impurities – Certain forms of carbon contains elements that can suppress the evolution of hydrogen at the negative improving charge efficiency.

(4) Capacitive contribution – The added carbon acts as an asymmetric super capacitor, storing charge at high rates in the electric double layer and spontaneously discharging, converting PbSO4 into lead.

(5) Intercalation of hydrogen into the graphite structure – The graphite structure allows for intercalation sites for the hydrogen atoms that support the cells’ capacity.

While the exact mechanisms of EAC in the

negative plate are still being investigated, a number of variations on the concept of a carbon negative are being utilized within the industry.

The method utilized for this application has focused on maintaining the negative electrode in a continuous PSoC and provides equivalent cycle life as if operating at a full state of charge.

ACKNOWLEDGMENTS The authors would like to thank the members of

We Energies (Wisconsin Electric Power Company) for their input and expertise in the development of this application.

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REFERENCES [1] B. Hans, Lead-acid batteries, New York: Wiley, 1977. Print.

[2] D. Pavlov, T. Rogachev, P. Nikolov, and G. Petkova, “Mechanism of action of electro-chemically active carbons on the processes that take place at the negative plates of lead-acid batteries,” Proc. of 7th International Conference on Lead-Acid Batteries, Varna, Bulgaria, Varna: IEES, 2008. Print.

[3] P.T. Mosley, “Consequences of including carbon in the negative plates of Valve-regulated Lead Acid batteries exposed to high-rate partial-state-of-charge operation,” Journal of Power Sources 191.1, 2009, pp. 134-138. Print.

[4] M. Calabek, K. Micka, and P. Braca, “Significance of Carbon Additive in Negative Lead-Acid Battery Electrodes,” J. Power Sources 158, 2006, pp. 864-867.

BIOGRAPHICAL NOTE Conference presenter: Jon Anderson, Director New Technology Develop-ment, C&D Technologies Inc., Blue Bell, PA

Jon Anderson is currently the Director of New Technology Development for

C&D Technologies Inc. He and his group are responsible for research and development at C&D, including emerging technologies and systems development. His current work focuses on the development of active materials and advanced processing methods for valve-regulated lead-acid (VRLA) batteries, energy storage systems for renewable energy applications, and lithium-ion batteries for stationary power applications. He has worked in the energy storage industry for over 12 years, holding various technical positions in the United States and Europe. Mr. Anderson’s technical background is in Materials Science and Engineering and the early portion of his career was focused on alloys and active materials development for VRLA batteries for stationary and traction applications.

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41

DETERMINING STORAGE RESERVES FOR REGULATING SOLAR VARIABILITY ON THE ELECTRIC POWER GRID

Benjamin L. Norris

Clean Power Research, 1700 Soscol Ave. #22, Napa, CA, USA

One of the foremost technical challenges of

accepting high levels of solar photovoltaic (PV) energy onto the state power grids is the high speed variability of PV caused by cloud transients. Depending upon the magnitude and speed of these power output changes, significant levels of regulation reserves would potentially be needed, and may even make high-penetration targets impractical.

The issue is particularly pressing in light of aggressive state renewable energy targets. For example, to meet California’s Renewable Portfolio Standard (RPS) goal of 33% renewables by 2020, industry experts anticipate that the resource mix will include about 5,000 megawatts (MW) of PV in only 10 years. The extent to which these resources will require regulation, however, is at present unknown, and the energy storage industry and grid operators alike will benefit from models and tools that address the issue.

This paper presents a unique approach to quantifying PV variability by using satellite-derived solar data. The methodology will allow grid operators to forecast PV fleet output and to quantify fleet variability, given the design attributes and locations of individual PV systems. The methodology uses advanced algorithms for tracking cloud patterns, calculating PV plant correlation coefficients, and quantifying diversification effects in a manner that could be used at the control area level.

Initial validation of the model was performed using a network of high-speed solar irradiance data loggers in and around Napa, California. The first test included a network of 25 devices spaced 100 meters apart in a grid representing the spread of a 4-MW plant. The second test redeployed these devices in a 4-kilometer (km) grid (see Figure 1) representing a 400-MW plant. The results were used to confirm the model accuracy and quantify the diversification (Figure 2).

The satellite imagery thus collected lends itself to solar plant forecasting, fleet output forecasting, and fleet variability forecasting. These methods could be used by the Independent System Operators (ISOs) and Regional Transmission Organizations (RTOs) for more accurately planning and scheduling regulation reserves— including storage resources— in anticipation of seasonal and daily periods of high variability. Accuracy in quantification of needed regulation would avoid the two extremes of grid instability on the one hand and overcommitment of resources on the other.

A sample calculation of required reserves is presented for the California ISO control area using the California Public Utilities Commission Long Term Procurement Planning/Renewables Integration figures. This calculation illustrates the procedure for calculating required regulation reserves for 471 PV plants having a combined capacity of 5,434 MW.

This ongoing work has direct implications for the energy storage community as it relates to the market needs for regulation in each of the continent’s eight North American Electric Reliability Corporation (NERC) regions.

Fig. 1. 1 km × 1 km irradiance grid in Napa, California.

42

Fig. 2. Diversification effects for 25 sensors, November 21, 2010.

BIOGRAPHICAL NOTE Conference presenter: Ben Norris has managed technical and economic assessments of grid-connected renewable and storage technologies in the electric power industry for 26 years. His experience covers photovoltaics,

solar thermal electric, flywheels, advanced batteries, and fuel cells. He has developed methods for dynamically managing transmission line thermal ratings and for effectively using infrared imaging in transmission and distribution maintenance. Mr. Norris currently manages the Consulting Group at Clean Power Research in Napa, California. Clients include research organizations, financial institutions, utilities, and manufacturers in the United States and abroad. He studied Mechanical Engineering at Stanford University and served on the Board of Directors for the Electricity Storage Association for 8 years.

43

RECENT APPLICATIONS OF SODIUM-SULFUR (NAS)

BATTERY SYSTEM IN THE UNITED STATES AND IN JAPAN

Tetsuya Hatta

NGK Insulators, Ltd., Nagoya, Japan

ABSTRACT

NGK’s sodium-sulfur (NAS) battery is an advanced energy storage system developed for power grid applications. Megawatt-scale NAS battery systems were first operated in the field more than 10 years ago. Although the basic design concept of NAS battery cells and modules has not changed, the technology has been improved through many field demonstrations and commercial installations. Initially, the target application for NAS batteries was load-leveling, and that remains its primary use. Later, NAS batteries began to be used as standby power sources with load leveling capability. Recently, NAS battery applications have focused on stabilizing fluctuating power from renewable energy resources, such as wind turbines or photovoltaic generators. More than 300 megawatts of NAS battery systems have been installed globally. This presentation addresses a NAS demonstration project in the United States and a new, very large project in Japan. A new type of NAS battery under development is also introduced.

Keywords: sodium-sulfur battery, load leveling, peak shifting, renewable

NAS DEMONSTRATION PROJECT

BY XCEL ENERGY [1] Various demonstrations, including peak shaving,

frequency regulation, wind-smoothing, and wind leveling, have been conducted by using the 1-megawatt (MW) sodium-sulfur (NAS) battery system installed in Luverne, Minnesota, for Xcel Energy in 2008 (see Figure 1). That demonstration confirmed the technical capabilities of NAS Batteries for these applications. In addition, that project is the first demonstration of NAS batteries in severely cold climates such as occur in Minnesota. NGK designed a battery enclosure to maintain adequate interior temperatures down to exterior temperatures as low as -45 °C, demonstrating that NAS batteries can be deployed in very cold climates.

Fig. 1. NAS battery for Xcel Energy.

System Description

At the Xcel site, a 1-MW NAS battery system is installed proximate to a 11.5-MW wind farm comprised of seven wind turbines and connected to a 34.5-kilovolt power grid. The wind-generation and battery system is connected to a transmission line that operates within the jurisdiction of the Midwest Independent Transmission System Operator (MISO). An objective of this demonstration was to evaluate different ratios of installed wind capacity to energy storage capacity. Generation from the 11.5-MW wind farm was scaled to simulate wind output over the range of 1 MW to 10 MW.

Demonstration of Wind Leveling

In the wind-leveling operating mode, the operator specifies the scheduled power output of the combined wind and battery system at 30-minute intervals. When power output from the wind farm deviates from the scheduled value, the NAS battery system charges or discharges energy to compensate for the difference. The results of variable 1-MW wind generation and 1-MW battery stored energy compensation cases are shown in Figure 2. The NAS battery system responded to changes in the output from the wind farm rapidly and accurately, and it compensated for the difference between the scheduled power and the power generated by the wind farm.

44

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Fig. 2. Wind leveling, 1-MW wind and 1-MW NAS battery.

80-MW NAS BATTERY PLANNED FOR NORTHERN JAPAN

During the massive earthquake that occurred on March 11, 2001, several thermal power plants owned by Tohoku Electric Power and located along the Pacific coast were damaged by the earthquake. The damages were so severe that the power supply capabilities of the affected thermal power plants are not reliable for the time being. Tohoku Electric Power is making every effort to procure the power supply needed to meet the demand for power in their service area. They have decided to install 80 MW of NAS batteries as one measure to provide reliable power immediately. The NAS batteries will be charged when demand is low and discharged when the demand is high. The NAS battery system is expected to reduce peak demand and balance supply in the Tohoku area.

Location of the 80-MW NAS Battery Site

The NAS battery system will be installed at the Noshiro thermal power plant in Northern Japan (see Figure 3). The power plant is owned and operated by Tohoku Electric Power and was not damaged during the earthquake. The generating capacity of Noshiro thermal power plant is 1,200 MW.

Service Area ofTohoku Electric Power

Noshiro thermal power plant





Fig. 3. Location of the Noshiro Thermal Power Plant.

System Description

The NAS battery system to be installed at Noshiro is rated at 80 MW and can store 480 megawatt hours (MWh) of energy. The system consists of 40 sets of 2-MW NAS battery units. When completed, it will be the largest NAS battery installation in the world. The NAS battery modules and related systems at Noshiro will be installed inside of building. An interior “rack system” to support the NAS battery modules has been adopted to shorten the delivery and construction time. The same rack system was used in the 4-MW NAS battery installation at Presidio, Texas, for Electric Transmission Texas, LLC (ETT) and American Electric Power (AEP) (see Figure 4). The advantages in lead time offered by this approach were verified through the ETT/AEP project.

Fig. 4. NAS battery modules with rack system for ETT/AEP.

Schedule

The installation work is currently going on and the operation of the battery is scheduled to start in January 2012. Because this NAS battery system is intended to supply the power when the demand power is at its peak, it is desired to be ready to operate in the coming winter season. It is challenging for NGK to install such a large-scale NAS battery system in such a short period of time. In cooperation with Tohoku Electric Power and other related companies, NGK is making every effort to expedite the installation of NAS equipment.

Remarks

A total of about 230 MW of NAS batteries have been installed in the Tohoku and Kanto regions of Japan where intense ground motions occurred during the earthquake. Most NAS installations were ready to

45

use soon after grid power was recovered. The NAS battery’s robustness, as well as the short lead time needed for its installation, when compared to other power sources, are being recognized by electric power companies and consumers.

NEW TYPE OF NAS BATTERY UNDER DEVELOPMENT

The discharging duration of current NAS battery is 6 to 8 hours. Though the long discharging duration is one of the advantages of the NAS battery, some applications, such as ancillary services, do not require such a long discharging duration. NGK is developing a NAS battery with a discharging time of 1 to 2 hours. The cost per discharging power ($/MW) of the new type will be reduced compared with the current type.

REFERENCES [1] J. Himelic and F. Novachek, “Sodium Sulfur Battery Energy Storage And Its Potential To Enable Further Integration of Wind (Wind-to-Battery Project), Data Collection and Analysis Report (Milestone 5),” 2010.

BIOGRAPHICAL NOTE Tetsusya Hatta is Manager of the Engineering Department, NAS Battery Division, NGK Insulators, Ltd. His specialty is electric engineering. He has worked in the research and development and engineering

divisions. Since 2008, he has been involved in engineering and system development of NAS battery systems to be installed in the United States and other countries.

46

Session 3 – UK Research – Innovative Technologies

48

49

TECHNO-ECONOMIC MODELLING OF A UTILITY-SCALE REDOX FLOW BATTERY SYSTEM

Edward P.L. Roberts and D.P. Scamman

University of Manchester, Manchester, UK

ABSTRACT

A one-dimensional numerical model has been developed for redox flow battery (RFB) systems with bipolar flow-by electrodes, soluble redox couples, and recirculating batch operation. Overpotential losses were estimated from the Butler-Volmer equation, accounting for mass-transfer. The model predicted the variation in concentration and current along the electrode and determined the charge-discharge efficiency, energy density, and power density. The model was validated using data obtained from a pilot-scale polysulphide-bromine (PSB) system commercialized by Regenesys Technologies (UK) Ltd. The model was able to predict cell performance, species concentration, current distribution, and electrolyte deterioration for the Regenesys system. Based on 2006 prices, the system was predicted to make a net loss of 0.45 p kWh−1 at an optimum current density of 500 A m−2 and an energy efficiency of 64%. The economic viability was found to be strongly sensitive to the kinetics, capital costs, and the electrical energy price differential.

Keywords: Redox flow battery, polysulphide bromine, techno-economic modelling

INTRODUCTION

Redox flow batteries (RFBs) have been investigated for many years as chemical stores of electrical energy [1], and are the closest storage technology to widespread commercialization. RFBs have numerous advantages over other batteries, including a separation of the energy and power rating, modular systems, repeatable cyclic behavior, and the use of benign chemicals at atmospheric temperature and pressure. Redox couples currently under development for use in RFBs include polysulphide-bromine (PSB) [2], vanadium-vanadium [3], vanadium-polyhalide, cerium-zinc [4] and lead-lead. Numerical modelling of RFB systems for energy storage applications allows the technical and commercial performance of different designs to be predicted without costly lab, pilot, and full-scale testing.

In this paper we develop a numerical model of a RFB system, and apply this to the Regenesys Technologies Ltd. Pilot-scale PSB-based RFB. Numerical modelling can be used to obtain key parameters such as the electrochemical rate constants for the reactions. Furthermore, once validated, the model has been used to evaluate and

optimize the design and performance of a full-scale commercial RFB system.

METHODOLOGY The RFB numerical model developed in this

paper performed the following functions:

• Evaluation of mass transport (from the electrolyte bulk to the electrode surface) and reaction kinetics (described by the Butler-Volmer equation) as rate-determining processes.

• Estimation of the variation in concentration, overpotential, current density, exchange current density, and limiting current density up the electrode in a one-dimensional model.

• Calculation of the variation in cell performance during charge-discharge cycles and overall system characteristics including energy efficiency, power density, and energy density.

• Consideration of different operating conditions and electrolyte systems, e.g., variable redox couple, applied current density, power rating, operating temperature, catalyst, cycle length, species

50

concentration, electrolyte velocity, electrode area, stack size, tank volume, electrolyte conductivity, and membrane conductivity.

The main assumptions used in the model are

listed below:

• Single-step electrochemical reactions involving dissolved electro-active species were assumed to occur at the electrodes.

• Electrochemical kinetics were assumed to be described by the Butler-Volmer equation.

• Electrochemical rate constants and mass-transfer coefficients were assumed to be approximately constant.

• The effects of electro-migration were assumed to be negligible.

• Adsorption, electrode resistivity, and shunt current effects were assumed to be negligible.

• The current efficiency was assumed to be 100%, i.e., side reactions were not considered.

• Plug flow conditions were assumed to occur in the cells.

• Conditions were assumed to be the same in each cell in a stack.

The energy storage plant specification was

based on the first utility-scale PSB storage plant constructed by Regenesys Ltd. (although for commercial reasons the plant was never commissioned). The plant was constructed using XL200 modules, which consisted of 200 XL cells assembled to form a bipolar stack. These modules were rated at 120 kilowatts (kW) assuming a current of 400 amperes and a cell voltage of 1.5 volts. The plant was specified to give a power output of 15 megawatts (MW) and an energy storage capacity of 120 megawatt hours (MWh) (corresponding to an 8-hour discharge). Sodium bromide (NaBr) and Na2S4.8 electrolytes were used in the sulphide and bromide tanks respectively, with [Br]T,BOC = 4.5 M and [S]T,BOC = 4.8 M. The electrolyte volume was adjusted in order to deliver 120 MWh of capacity.

In terms of lifetime, the limiting component was expected to be the membrane, which typically lasts 15 years in the harsher chlor-alkali industry. The plant life was therefore assumed to be 15 years, with around 250 cycles of utilization per year. While the model was capable of modelling self-discharge over a long series of cycles, the effect of

self-discharge was not included in this study. In practice, electrolyte conditioning would be required to keep the system in balance. It was therefore assumed that conditioning was carried out regularly, so that the same performance could be expected on each cycle.

Obtaining accurate data on the capital cost of process equipment, particularly for a technology that has not been established, is extremely challenging. For this study, an approximate capital cost has been estimated based on a “best-case” scenario for the commercial performance, assuming a mature RFB industry has been established. The capital cost model was based on an existing model of a PSB system that predicted a capital cost of £320 kW-1 [5]. This model assumed 1995 UK prices, a production rate of 400 MW per year of 200 kW-rated modules, mature production costs (representing the middle of the growth phase of the product life cycle), and modularization and standardization of plant designs. It was assumed that increased costs due to inflation since 1995 would be offset by savings associated with technological improvements. The capital cost is divided into three elements: electrochemical cells (including balance of plant), electrical equipment and electrolyte and tanks [5]. The economic parameters used are shown in Table 1.

Table 1. Parameters used in the economic model. Overall Required delivered

energy 120 MWh per

cycle at 15 MW

Charge/discharge period

8 hours

Frequency of charge cycles

250 cycles year−1

Plant lifetime 15 years

Capital cost Installed module capital cost

£41,000 Nm0.9

Electrical plant cost £60 kW−1 on charge

Electrolyte/tank cost £350 m−3 Running

Costs and Income

Pump efficiency, πp 35% Transmission losses 5 % on

discharge Cost of electricity

consumed 2.3 p kWhr−1

Value of electricity delivered

5.7 p kWhr−1

Net Present Value

Calculation

Inflation rate, a 2.5% Discount rate, r 10%

Net present value factor 9.25 years

51

RESULTS AND DISCUSSION The overall cost of the delivered energy was

calculated for a range of operating current densities (Figure 1). At low current density the cost of the electrochemical modules was the largest part of the cost. As the current density increased, this cost decreased rapidly, but at high current density the cost of inefficiency (i.e., energy lost on charging) increased significantly. Thus an optimum current density of around 500 A m−2 was obtained.

Fig. 1. Breakdown of the cost of delivered energy at a range of current density.

For arbitrage applications, the electricity costs shown in Table 1 were estimated based on UK electricity market prices from 2006. Figure 2 shows the net profit obtained showing that the process is uneconomic for the conditions studied. However, the loss is less than 0.5 p kWh−1 at the optimum current density and it is likely that improved performance and/or changes in the electricity market are likely to make the technology profitable within the next decade

Fig. 2. Effect of current density on net profit.

REFERENCES [1] M. Bartolozzi, “Development of redox flow batteries. A historical Bibliography,” J. Power Sources 27, 1989, pp. 219-234.

[2] A. Price et al., “A novel approach to utility-scale energy storage,” Power Eng. J. 13, 1999, pp. 122-129.

[3] E. Sum and M. Skyllas-Kazacos, “A study of the V(II)/V(III) redox couple for redox flow cell applications,” J. Power Sources 15, 1985, pp. 179-190.

[4] B. Fang et al., “A study of the Ce(III) and Ce(IV) redox couple for redox flow battery application,” Electrochim. Acta 47, 2002, pp. 3971-3976.

[5] F. Walsh, A first course in Electrochemical Engineering, The Electrochem. Consultancy, 1993.

BIOGRAPHICAL NOTE Conference presenter: Dr. Roberts is a Reader at the School of Chemical Engineering at the University of Manchester. He is an electrochemical engineer with 20 years of research experience on a wide range of technologies for energy and environmental

applications. He has published more than 50 papers in international peer-reviewed journals and holds eight patents and patent applications. His research interests have covered a wide range of topics, including nanomaterials/electrocatalysis, electro-kinetic treatment of contaminated land, electrosynthesis, water and waste treatment, metal recovery, fuel cells, and redox flow batteries. Dr. Roberts is a co-founder and Research Director of Arvia Technology Ltd., a successful University spin-out company that is commercializing a waste and water treatment technology. His work has been recognized through a number of awards including the European Academic Enterprise (ACES) Fast Start-up award (2009), the IET Innovation Award for Sustainability (2009), and the IChemE Water Innovation Award (2008). Dr. Roberts is a Fellow of the IChemE, a committee member and former chair of the SCI Electrochemical Technology Group, and a member of the European Federation of Chemical Engineers working party on electrochemical engineering.

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53

SUBSTRATES FOR THE POSITIVE ELECTRODE REACTION IN THE ZINC-CERIUM REDOX FLOW BATTERY

G. Nikiforidis, L.E.A. Berlouis,1 D. Hall,1 and D. Hodgson2

WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow G1 1XL, UK

1C-Tech Innovation Ltd., Chester, UK; 2www.vallontia.com

ABSTRACT The key to maintaining the high open circuit values of the zinc-cerium redox flow battery during charge and

discharge is to minimize the overpotential losses by careful choice of electrodes and current densities employed as well as cell design. This study examined the positive electrode reaction on a variety of electrode substrates consisting of coatings of platinum, platinum/iridium, and titanium/tantalum on titanium substrates as well as commercial DSAs in order to assess the electron transfer kinetics of the Ce3+/Ce4+ reaction and so allow benchmarking for future developments to take place.

The zinc-cerium hybrid redox flow batteries (RFBs) [1] have one of the largest open circuit values (~2.4 volts) of any current RFB system. The key to maintaining this as high as possible during charge and discharge is to minimize the overpotential losses by careful choice of electrodes and current densities employed as well as cell design. In this study, the positive electrode reaction, i.e., Ce4+ + e− Ce3+, was examined on a variety of electrode substrates consisting of platinum (Pt), platinum/iridium (Pt/Ir), and titanium/tantalum (Ti/Ta) as well as commercial DSAs in order to assess the electron transfer kinetics and so allow benchmarking for future material developments to take place. The experiments were performed over the temperature range 24 ºC to 60 ºC in methane sulphonic acid (MSA) as the base electrolyte with the cerium concentration set at 0.8 M. The techniques of cyclic voltammetry, Tafel extrapolation, polarization resistance, electrochemical impedance spectroscopy (EIS), as well as rotating disk (RDE) techniques were employed in order to assess the performance of the different electrocatalytic coatings for the Ce3+/Ce4+ reaction.

For the electrode substrates employed, it was important that the available electroactive surface area was correctly determined and for this, both the underpotential hydrogen evolution reaction and

carbon monoxide adsorbed layer oxidation regions in 1.0 M sulfuric acid (H2SO4) were employed [2,3]. For a geometric area of 1 centimeter squared (cm2), the electroactive areas for the coated samples were found to be in the range of 75 cm2 to 125 cm2, depending on the preparation procedure. Typical results from polarization resistance and Tafel extrapolation measurements obtained from the samples are shown in Figures 1 and 2, respectively. Exchange current densities were in the range 1.7 × 10-6 A cm−2 to 1.0 × 10-4 A cm−2 for the Pt-Ir catalysts and between 2.0 × 10-7 A cm-2 and 9.5 × 10-5 A cm-2 for the sole Pt-based respectively. Ta-based electrodes seemed to inhibit the oxygen evolution process but the electrochemical kinetics for the oxidation of Ce(III) and the subsequent reduction of Ce(IV) were also correspondingly very slow (∼10-7

– 10-8 A cm−2). Exchange current densities on the iridium-oxide-coated electrodes were between 3.5 × 10-5 A cm−2 and 8 × 10−5 A cm-2. However, for all the range of substrates investigated, an increase in temperature to 60 ºC favored the kinetics of the Ce3+/Ce4+ reaction as higher exchange current densities were recorded. EIS measurements were also conducted on the substrates at 25 ºC (Figure 3) and the data obtained were in good agreement with the data from the above two other techniques.

54

Fig. 1. Polarization resistance on Pt-Ti mesh electrode at 298 K. Scan rate: 0.1667 mV s-1.

Fig. 2. Tafel analysis on Pt-coated electrode (3 g cm-2 of Pt) at 333 K. Scan rate: 2 mV s-1.

Fig. 3. Impedance data at halfwave potential (0.75 V) on Pt-coated electrode (5 g m-2 etched) at 298 K.

Under the flow regimes used, charge-discharge cycles on the Pt disk and Pt/Ti mesh electrodes revealed as expected 100% coulombic efficiencies in a solution consisting of 0.2 M Ce4+ in 6.9 M MSA at current densities <100 mA cm−2 (Figure 4). However, at higher current densities, the sharp increase in potentials suggest that oxygen (during charging) and hydrogen (during discharge) evolution reactions are occurring with resulting loss in current efficiency at these electrodes.

Data will also be presented for the complete Zn-Ce hybrid RFB where the overall current, voltage, and energy efficiencies as a function of current density are determined during multiple charge-discharge cycles.

Fig. 4. Galvanic cycles at different charge current densities under solution flow in 0.2 M Ce4+ in MSA - 333 K -Pt-Ti mesh (Geometric area: 4 cm2).

REFERENCES

[1] http://plurionsystems.com/tech_flow _technology.html.

[2] T. Biegler, D.A. Rand, R. Woods, “Limiting oxygen coverage on platinized platinum; Relevance to determination of real platinum area by hydrogen adsorption,” J. Electroanal. Chem. 29, 1971, pp. 269-277.

[3] R. W. Lindström, K. Kortsdottir, and G. Lindbergh, “Active area determination for porous Pt-electrodes used in PEM fuel cells. Temperature and humidity effects.” Applied Electrochemistry, School of Chemistry and Engineering, KTH Royal Institute of Technology SE-10044 Stockholm, Sweden.

Rp (Ohms/cm2)= 0.60766Io (Amp/cm2)= 0.04293Eo (Volts)= 0.91446

0.90 0.91 0.92 0.93-0.03

-0.02

-0.01

0

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I (Am

ps/c

m2 )

19-02-2011 0.2 M Ce4+ Pt-Ti mesh 298 K pol 2.corRpFit Result

Bc (mV)= -273.79Io (Amp/cm2)= 0.0026017Eo (Volts)= 0.90442

Ba (mV)= 210.16Bc (mV)= -273.79Io (Amp/cm2)= 0.0025881Eo (Volts)= 0.90504

0.6 0.7 0.8 0.9 1.0 1.1 1.210-6

10-5

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10-03-2011 0.2 M Ce4+ SL5 333 K Tafel 1.corTafelFit Result

10-1 100 101 102 103 104 105100

101

102

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15-03-2011 0.2 M Ce4+ SL3 at 0.75 V.ZFitResult

10-1 100 101 102 103 104 105

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theta

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55

BIOGRAPHICAL NOTE Conference presenter: Dr Len Berlouis is a Reader in Physical Chemistry in the Department of Pure and Applied Chemistry at the University of Strathclyde, Glasgow, Scotland. He obtained his Ph.D. from Southampton University (England,

UK) in 1982 working on AC impedance characterization of flow-through porous electrodes. He then worked as a research scientist at the Wolfson Centre for Electrochemical Science (Southampton) for 9 years on projects ranging from electropolymerisation, corrosion studies, sensors, semiconductor electrochemistry, and interfacial spectroelectrochemistry. He moved to the University of Strathclyde in 1991, and since then he has extended his work involving optical techniques (ellipsometry, electrolyte electroreflectance, and second harmonic generation ([SHG]) for characterizing solid/electrolyte interfaces. This led to a number of publications as well as presentations (orals and posters) at international conferences. In more recent years, the technique of SHG in particular was extensively used to examine the surfaces of

epitaxial semiconductor single crystals and the effect of mismatch between the substrate and the epitaxial layer. The adsorption of small molecules/atoms at single crystal metal surfaces (e.g., platinum, gold) was also followed with these techniques as well as changes in surface symmetry and reconstruction as a function of applied potential. Here, the electroreflectance technique as well as surfaced enhanced Raman scattering (SERS) were employed to good effect. He has been an active researcher in redox flow battery systems for the last three years working in close collaboration with Plurion Ltd., Glenrothes, Scotland, as well as colleagues from the University of Southampton, England, and has presented this work at major international conferences.

He has over 70 peer-reviewed publications and has had active international collaborations with the Electrochemistry Groups at the École Polytechnique Fédérale de Lausanne (Switzerland), the Department of Physical Chemistry, University of Alicante (Spain), the Laboratoire de Spectrométrie Ionique et Moléculaire at the Université Claude Bernard, Lyon (France), the Solidstate Physics Laboratory, Delhi (India) and SRI International, Menlo Park, California.

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57

THE DEVELOPMENT OF FLOW BATTERIES FROM

PROOF OF CONCEPT TO PILOT SCALE (AND BEYOND)

R.G.A. Wills,1,2 C. Ponce de Leon,1 and F.C. Walsh1,2

1University of Southampton, Southampton, United Kingdom 2Research Institute for Industry (RIfI), Southampton, United Kingdom

ABSTRACT

Flow batteries have been suggested for applications such as the integration of renewable energy technologies, stand-by power, and as a tool for improving power transmission/distribution in electricity networks. A large number of chemistries have been identified, some of which are under commercial development, while others have only been characterized on a small laboratory scale or are impractical. The chemical and engineering challenges associated with developing a flow battery from proof of concept to a commercial system are discussed. Performance data from chemistries currently being developed at the University of Southampton will be used to provide specific examples of flow battery operation and development.

Keywords: flow battery, lead-acid, all-vanadium, zinc-air, zinc-cerium

INTRODUCTION

Successful development of a flow battery involves overcoming both chemical and engineering challenges. At the proof of concept stage, chemistry dictates progress with reversible, efficient electron transfer and compatibility between electrolyte components being paramount. Scaling up towards commercially viable systems, engineering plays a larger role, with stack design optimization and system costs defining success. This paper outlines some of the critical parameters and challenges involved in this process and uses case studies from systems being developed at Southampton University to provide illustrative data.

Chemistries

The selection of active species for the positive and negative electrode reactions influences system choices such as electrode material, electrolyte composition, membrane material, and cell design. Various categories of flow battery can be envisaged, determined by the electrode reactions. Examples of possible systems include:

All-vanadium – Classical, membrane-divided redox flow battery utilizing active species that remain solvated during charge and discharge cycling.

𝑉3+ + 𝑉𝑂2+ + 𝐻2𝑂 𝑉2+ + 𝑉𝑂2+ + 2𝐻+

Zinc-cerium – Half redox flow battery and half metal flow battery. Membrane divided. Cerium ions remain solvated during charge/discharge cycling, whereas a phase change is required at the negative electrode, where metallic zinc is deposited during charging.

𝑍𝑛2+ + 2𝐶𝑒3+ 𝑍𝑛 + 2𝐶𝑒4+

Soluble lead – Metal, metal oxide flow battery that does not require a membrane as a single active species, Pb2+, is present in the electrolyte and both electrode reactions involve depositing solid phases during charging.

2𝑃𝑏2+ + 2𝐻2𝑂 𝑃𝑏 + 𝑃𝑏𝑂2 + 4𝐻+

Zinc-air – Half metal flow battery, half unitized fuel cell. The negative electrode reaction involves a phase change between solvated Zn2+ ions and metallic zinc. The positive electrode is air breathing and similar to a polymer electrolyte membrane (PEM) fuel cell, where a catalyst system is required for oxygen evolution and reduction during charge and discharge respectively.

𝑍𝑛2+ + 𝐻2𝑂 𝑍𝑛 + 12𝑂2 + 2𝐻+

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Case Study: Soluble Lead

A flow battery based on the two redox couples Pb/Pb2+ and Pb2+/PbO2 and a single electrolyte consisting of a high concentration of lead methanesulfonate in methanesulfonic acid has been developed from fundamental chemistry (voltammetric studies at a rotating disc electrode) to a pilot-scale flow reactor (bipolar stack with five 1000-cm2 electrodes) (see Figure 1). This system has the advantage that no membrane is necessary but it does require the controlled deposition and dissolution of solid phases on both electrodes. The battery has an open circuit potential of ~1.8 volts (V) and can have an energy efficiency >70% and a cycle life exceeding 100 deep charge/discharge cycles. The power density on discharge peaks at approximately 1.2 V, which corresponds to 160 mW cm-2 (see Figure 2).

Fig. 1. Pilot-scale flow reactor.

Fig. 2. Power density on discharge.

Successful mitigation of battery failure modes

was required during scale-up from laboratory cell to pilot rig. Possible failure processes associated with the cell chemistry have been defined; lead (Pb) dendrites, lead dioxide (PbO2) creep, and PbO2 sludging. All

three processes result in electrical shorting between the positive and negative electrodes. Dendritic Pb growths typically occur during high-current charging. PbO2 creep refers to solid, well-adhered PbO2 deposits growing over the polymer cell components, eventually bridging the inter-electrode gap. PbO2 sludging refers to amorphous, gel-like deposits forming from debris removed from the positive electrode. These deposits build up in areas of low electrolyte flow and through sedimentation onto horizontal cell components, such as electrode spacers and inlet manifolds. Optimizing mass transport through the flow chamber (cell design) and the use of selected electrolyte additives minimizes these failure modes.

REFERENCES [1] R.G.A. Wills and F.C. Walsh, Flow batteries, in Encyclopedia of Electrochemical Power Sources, 2010, Elsevier: Amsterdam., pp. 745-749.

[2] R.G.A. Wills et al., “Developments in the soluble lead-acid flow battery,” J. Appl. Electrochem. 40, 2010, pp. 955-965.

[3] M.J. Watt-Smith, R.G.A. Wills, and F.C. Walsh, Secondary batteries - flow systems, in Encyclopedia of Electrochemical Power Sources, 2010, Elsevier: Amsterdam., pp. 438-443.

[4] A.A. Shah et al., “A Mathematical Model for the Soluble Lead-Acid Flow Battery,” J. Electrochem. Soc. 157(5), 2010, pp. A589-A599.

[5] D. Pletcher et al., “A novel flow battery - A lead acid battery based on an electrolyte with soluble lead(II). Part VI. Studies of the lead dioxide positive electrode,” J. Power Sources, 180, 2008, pp. 630-634.

[6] D. Pletcher et al., “A novel flow battery - a lead acid battery based on an electrolyte with soluble lead(II). V. Studies of the lead negative electrode,” J. Power Sources, 180, 2008, pp. 621-629.

[7] D. Pletcher and R.G.A. Wills, “A novel flow battery - A lead acid battery based on an electrolyte with soluble lead(II). III. The influence of conditions on battery performance,” J. Power Sources, 149, 2005, pp. 96-102.

[8] A. Hazza, D. Pletcher, and R.G.A. Wills, “A novel flow battery - A lead acid battery based on an electrolyte with soluble lead(II). IV. The influence of additives,” J. Power Sources, 149, 2005, pp. 103-111.

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[9] D. Pletcher and R.G.A. Wills, “A novel flow battery: A lead acid battery based on an electrolyte with soluble lead(II). Part (II). flow cell studies,” Phys. Chem. Chem. Phys. 6, 2004, pp. 1779-1785.

[10] A. Hazza, D. Pletcher, and R.G.A. Wills, “A novel flow battery: A lead acid battery based on an electrolyte with soluble lead(II). Part I. Preliminary studies,” Phys. Chem. Chem. Phys. 6, 2004, pp. 1773-1778.

[11] P.A. Leung, C. Ponce-de-Leon, C.T.J. Low, A.A. Shah, and F.C. Walsh, “Characterization of a zinc-cerium flow battery,” J. Power Sources 196(11), 2011, pp. 5174-5185.

[12] A.A. Shah, R. Tangirala, R. Singh, R.G.A. Wills, and F.C. Walsh, “A dynamic unit cell model for the all-vanadium flow battery,” J. Electrochem. Soc. 158(6), 2011, pp. A671-A677.

BIOGRAPHICAL NOTE Conference presenter: Dr Richard Wills is a senior research fellow with the Research Institute for Industry (RIfI) at the University of Southampton, UK. His research is focused on energy conversion technologies, in particular redox flow batteries, fuel cells, and electrode materials. He obtained a Ph.D. in Electrochemistry in 2004 working on a novel lead-acid flow battery. He then worked as a consulting engineer on a range of chemical, electrochemical, and energy storage projects until 2007. Between 2007 and 2008 he worked for Atraverda as a battery specialist developing ceramic and composite electrode materials before returning to RIfI in 2008 to further research the areas of batteries and electrochemical devices. He received the Dave Rice award in 2007 for research on lead-acid batteries.

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TEMPERATURE DEPENDENCE OF KEY PERFORMANCE INDICATORS FOR AQUEOUS ELECTROCHEMICAL CAPACITORS

CONTAINING NANOSTRUCTURED BIRNESSITE MANGANESE DIOXIDE

Alexander J. Roberts and Robert C.T. Slade

Chemical Sciences, University of Surrey, Guildford GU2 7XH, United Kingdom

ABSTRACT

Birnessite has been made in a number of morphologies through variation of reaction conditions in a simple templated hydrothermal synthesis. After processing into electrodes and testing in hybrid supercapacitor cells, good cyclability and a range of specific capacitances were observed. The most promising material, a birnessite nanotube, was extensively electrochemically tested at elevated temperatures. An increase in specific capacitance from around 250 to 450 F g-1 was observed as the temperature was raised from 30 to 80 ºC. There was a drop in specific capacitance with cycling at elevated temperatures and inferences have been drawn regarding the effects of both cycling and time spent at elevated temperatures.

Keywords: supercapacitor, MnO2, elevated temperature, nanostructured

INTRODUCTION A great deal of focused research on clean energy

technologies for both grid power applications and an alternative to the internal combustion engine is under way worldwide, prompted by concerns of global warming and environmental sustainability. The majority of these renewable technologies do not offer security of supply and require effective energy storage. Current battery and fuel cell technologies (also seen as the only viable alternatives to the internal combustion engine), do not offer the high power densities necessary to be used on their own. Furthermore, rapid charging and discharging of such devices is likely to significantly decrease their lifetime. Electrochemical supercapacitors are attracting much attention for use both alone and in conjunction with batteries and fuel cells, as they are known to enhance the lifetime of the system by virtue of their high power densities and rapid charge-discharge characteristics [1-4].

The energy storage characteristics of supercapacitors are dependent on the physiochemical characteristics of both the electrode materials and electrolyte [1, 4-8], with the energy stored through separation of charge via accumulation at the electrode surfaces (electrical double layer capacitance [EDLC])

[9] and also through faradaic redox processes at the electrodes (pseudocapacitance) [10]. Typical commercial supercapacitors consist of carbon or ruthenium(IV) oxide (RuO2) electrodes and an electrolyte with the highest specific capacitances being reported for hydrated RuO2-based systems (>700 F g-1), also showing good cycling ability but with problems of high cost and toxicity [10-13]. Of the metal oxides under investigation as an alternative, the most promising to date is manganese dioxide (MnO2) with in device specific capacitances over 450 F g-1 and high natural abundance, low toxicity, low cost, and low environmental impact. A further advantage of MnO2 is the range of phases and morphologies that can be attained through tailoring the manufacturing process [14-18]. Current attempts at improving performance usually center on maximizing specific surface areas and pore volumes and tailoring pore size distributions. It has been shown, however, that some birnessite MnO2 materials exhibit high specific capacitance despite relatively low specific surface areas [19]. This is believed to be a result of the small thickness of the birnessite platelets allowing access to almost all of the MnO2 by the electrolyte, effectively meaning that close to 100% of the material can be considered as close to the surface.

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In this study, birnessite has been made in a variety of morphologies through a simple templated hydrothermal route and tested in hybrid supercapacitor cells with a neutral aqueous electrolyte. The most promising of the materials has been subject to extensive electrochemical testing at elevated temperatures in order to assess the effect on key performance indicators such as specific capacitance, current leakage, and cycle lifetime, seen by the authors as essential for future application in automobile applications.

EXPERIMENTAL Materials Synthesis

Potassium permanganate (KMnO4) (0.0949 mol) was added to potassium hydroxide (KOH)(aq) (0.5988 mol, 180 cm3) and stirred for 30 minutes. Dodecylamine (0.0170 mol) was added and stirred for a further 30 minutes before being transferred to a Parr Hastelloy autoclave and heating to between 120 and 150 ºC for between 1 and 3 days with constant stirring (the resultant solids after washing and template removal are designated by reaction temperature and time, e.g., 1201D corresponds to 120 ºC for 1 day). After allowing the reaction to slowly cool to room temperature, the resulting solid was collected by centrifuge and washed several times with deionized water until the pH of washings corresponded to that of the starting water. The solid was then washed several times in ethanol, until all dodecylamine had been removed, checked by CHN analysis, before drying at 80 ºC overnight.

Electrodes for electrochemical characterization were prepared by mixing the material above with polyvinylidene fluoride (PVDF) and graphite in the ratio 85:5:10 in acetone with stirring for several hours to obtain a homogenous ink. The volume of the ink was reduced by heating to 85 ºC before spraying onto pre-weighed stainless steel current collectors and drying at room temperature. Carbon electrodes were prepared by the same method with MnO2 substituted by Darco G60 carbon (Aldrich).

Assembly of Supercapacitor Cells

One MnO2 and one carbon electrode were assembled in a hybrid arrangement separated by a glass fiber filter paper pre-soaked in (NH4)2SO4 (aq., 2 mol dm-3) electrolyte in custom test cells and were assembled to a constant torque of 2 N m-1.

Characterization Techniques

Powder X-ray diffraction (XRD) profiles were measured on a PANalytical X’Pert Pro PW3179

diffractometer using CuKα radiation and an X’Celerator detector. Nitrogen sorption was carried out at 77 K on samples previously outgassed at 150 ºC for 24 hours in a Micromeritics Flowprep 060 unit. The samples were then transferred to a Micromeritics V Surface Area and Pore Size Analyzer for analysis. Samples for electron microscopy were suspended in ethanol ultrasonically for 15 minutes before being deposited on Holey carbon discs and were analyzed using a Hitatchi HD-2300A Scanning Transmission Electron Microscope (STEM) at 200 kilovolts (kV). Galvanostatic cycling of the assembled test cells was carried out between 0 and 1.35 volts over 1000 cycles at various discharge currents on a Solatron 1480 Multistat with a 1255B Frequency Response Analyzer.

RESULTS AND DISCUSSION Powder XRD profiles of all materials

synthesized between 120 and 140 ºC were of the same form, examples of which are given in Figure 1. All of the peaks observed could be indexed to potassium birnessite (ICPDF No. 00-052-0556). As both the temperature and reaction time were increased, the degree of crystallinity and/or long-range order was seen to increase, evident by an increase in relative intensity and sharpness of the peaks.

2θ / o0 20 40 60 80

Inte

nsity

1201D

1302D

1403D

Fig. 1. Powder XRD profiles of 1201D, 1302D, and 1403D materials.

The profile observed in 1501D was of the same

form, but for both 1502D and 1503D additional peaks were observed (Figure 2), becoming more prominent as the reaction time was increased. These additional peaks could be matched to the manganite phase manganese oxyhydroxide (ICPDF No. 01-074-1842). Manganite formation has been reported during attempts to synthesize birnessite nanotubes [20] and has been previously observed under these conditions

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using hexadecylamine template, with the resulting electrodes showing a lesser specific capacitance than would be expected due to the presence of Mn(III) [21].

Nitrogen sorption at 77 K of all materials showed isotherms that could be classified as a combination of types I and IV as classified by BDDT [22] with a rapid uptake of nitrogen at low relative pressures (suggesting the presence of micropores) and no plateau observed at high relative pressures. Hysteresis was observed upon desorption (suggesting the presence of mesopores) with hysteresis loops classified as H3 and or H2 according to IUPAC classifications [23], suggesting a complex network of interconnected slit-shaped pores.

2θ / o0 20 40 60 80

Inte

nsity

1501D

1502D

1503D

*

* *

***

Fig. 2. Powder XRD profiles of 1501D, 1502D, and 1503D materials. Peaks corresponding to manganite are indicated by an asterisk (*).

BET analysis of the sorption isotherms showed

the specific surface areas to vary depending on reaction conditions between 45 and 128 m2 g-1 with total pore volumes, Vp, calculated from the nitrogen adsorption at p/po = 0.99 ranging from 0.17 to 0.72 cm3 g-1 (see Table 1). With the exception of 1302D, the specific surface areas were seen to increase as reaction time increased but decrease with increasing reaction temperature. Although no clear trend was observed with respect to reaction conditions and total pore volume, both the 120 and 140 ºC materials showed an increase with longer reaction times.

Pore size distributions calculated using Density Functional Theory showed their relationship with reaction conditions to be complex, dependent on both reaction time and temperature. At least two peaks

were observed in each case, with those of the materials formed at 150 ºC being at a higher pore diameter than those formed at lower temperatures.

Table 1. Specific surface area (SBET) and total pore volume (VP) of materials (as determined by BET and BJH analysis respectively) of the N2 isotherms at 77 K.

SBET / m2 g-1 Vp / cm3 g-1 1201D 108 0.17 1202D 116 0.35 1203D 128 0.60 1301D 46 0.09 1302D 100 0.22 1303D 48 0.09 1401D 84 0.17 1402D 84 0.19 1403D 87 0.59 1501D 45 0.72 1502D 48 0.22 1503D 64 0.33

Fig. 3. Electron microscopy studies: SEM images of (a) 1201D, (b) 1202D, (c) 1203D, (d) 1303D, (e) 1403D, and (f) 1503D. TEM images are shown as insets with scale bars representing 500 nm in (a) and (f), 200 nm in (b) and (e) and 20 nm in (c) and (d).

(b)

(d) (c)

(e) (f)

(a)

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Scanning and transmission electron micrographs (TEMs) of a number of the materials are shown in Figure 3. By inspection of the micrographs, it is apparent that small variations in reaction conditions have a major effect on particle morphology.

All of the materials were evaluated as potential supercapacitor electrodes through galvanostatic charge-discharge cycling in test cells in hybrid configuration with a carbon-based second electrode and (NH4)2SO4 (aq., 2 mol dm-3) electrolyte. The materials were cycled between 0 and 1.35 volts at a current density of 1 A g-1. The expected sawtooth charge-discharge profile was observed in all materials with the charge and discharge portions being symmetrical. Excellent cyclability was observed with coulombic efficiencies between 99 and 100% being observed after the first few cycles. The specific capacitance observed after 1000 cycles, ranging between 40 and 105 F g-1, are shown in Figure 4. The materials synthesized at 120 and 150 ºC showed increasing specific capacitance with increasing reaction time, following the same trend as specific surface area for the materials. Interestingly, no correlation was found between the total pore volumes and specific capacitance of these materials (the total pore volume in the 150 ºC materials decrease with reaction time, whereas those of the 120 ºC materials increase). No correlation could be inferred between the specific capacitance observed for the materials synthesized at 130 or 140 ºC and any of the properties measured in this work. This is likely due to the complex interaction (both positive and negative) of a number of contributing factors in the systems, with matters made even more complex by the presence of manganite in some of the higher temperature materials (as observed in XRD).

0

20

40

60

80

100

1201201D

1202D

1203D

1301D

1302D

1303D

1401D

1402D

1403D

1501D

1502D

1503D

Reaction conditions

Spec

ific

capa

cita

nce

/ F g

-1

Fig. 4. Specific capacitance of materials as obtained from galvanostatic cycling at a discharge current density of 1 A g-1.

One material was chosen for further electro-chemical evaluation at a variety of temperatures.

Criteria for material selection for this further study were cost, ease of processing, and preliminary specific capacitance. 1203D, 1401D, and all of the 150 ºC materials exhibited comparable high specific capacitance, all of which were suitable for further study on this basis alone. Of the materials showing a high specific capacitance, 1203D produced a stable ink that sprayed with ease when making test electrodes, with the other materials requiring tighter rheological control and much effort to obtain the same electrodes of the same quality. Given these facts and consideration that higher temperature during reaction would be likely to increase overall final cost, the material chosen for further study at varied temperatures was 1203D.

The effect of temperature on specific capacitance of 120D at various discharge current densities is shown in Figure 5. As the current density was increased the specific capacitance was seen to decrease at all temperatures. This was a result of kinetically controlled diffusion in the system. As the temperature was increased, a large increase in specific capacitance of almost 100% was observed at low current density; this became less significant at higher current densities. Little difference was observed in specific capacitance between 30 and 70 ºC in measurements at higher current densities, with a significant increase being observed as the temperature was increased between 70 and 80 ºC. This increase in specific capacitance can be explained by the fact that the kinetics of diffusion in the system will be greatly increased at higher temperatures, allowing a more rapid diffusion of NH4

+ ions into the electrode pore structure. It is believed that between 30 and 70 ºC the increase in temperature is not sufficient to increase the specific capacitance at higher discharge current densities, but at 80 ºC the diffusion is such that a large gain in specific capacitance is observed even at 10 A g-1 current density.

0

50

100

150

200

250

300

350

400

450

500

0 2 4 6 8 10

Discharge current / A g-1

Spec

ific

cap

acita

nce

/ F g

-1 30ºC50ºC70ºC80ºC

Fig. 5. Variation in specific capacitance of 1203D with discharge current density as a function of temperature.

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The effect of elevated temperature on the lifetime of supercapacitors was also investigated (Figure 6). Galvanostatic cycling at a discharge current density of 2.5 A g-1 at 30 ºC showed an initial increase in specific capacitance over the first few cycles, with little variation observed thereafter. At 50 ºC, after an initial increase in specific capacitance over the first few cycles, little variation was observed up to 700 cycles, after which a slow fade in specific capacitance began. At 70 ºC the initial increase in specific capacitance was followed after 200 cycles by a gradual decline up to 700 cycles, after which the specific capacitance showed little variation. At 80 ºC an initial rapid increase in specific capacitance over the first 200 cycles was followed by a rapid loss over the next 200 cycles, becoming more gradual thereafter but still decreasing at 1000 cycles. After 1000 cycles the specific capacitance at 80 ºC was lower than that at 50 ºC and comparable to that at 30 ºC. At 70 ºC the loss of specific capacitance had resulted in a final value lower than that at 30 ºC.

0

50

100

150

200

250

300

0 200 400 600 800 1000

Cycle

Spec

ific

cap

acita

nce

/ F g

-1 30ºC50ºC70ºC80ºC

Fig. 6. Effect of cycling at various temperatures on specific capacitance calculated from galvanostatic data.

The drop in specific capacitance during cycling at 80 ºC appeared greater than might be anticipated. Given that galvanostatic testing experiments such as this involve variable time, depending upon the specific capacitance, the devices exhibiting higher initial performance spend longer at elevated temperature than those at 30 and 50 ºC. As a result of this, and in an attempt to further understand the large drop in cycling performance at 80 ºC, the effect of time at elevated temperatures was also investigated. As can be seen in Figure 7, the specific capacitance at 30 ºC showed an initial increase over the first 3 days of storage, returning to its initial value after 28 days. At 50 and 70 ºC, a less significant increase was observed initially, followed by a rapid loss over the first day before stabilizing with little change observed after 10 days at temperature. When stored at 80 ºC, a large relative increase in specific capacitance was

again observed with a rapid and prolonged loss over the next 7 days or so. The specific capacitance was seen to continue to drop, approaching 0 after 15 days. These results suggest that the number of cycles performed at elevated temperatures may have a lesser effect on the lifetime of a supercapacitor device such as this than the amount of time the device spends at elevated temperatures. This was further emphasized when the cells were cycled at elevated temperatures at a charge rate of 10 A g-1. At the higher discharge current densities, the time at temperature still increased as the temperature increased (due to the increase in specific capacitance) but the difference in times at temperature was considerably less. In this case the specific capacitance after 1000 cycles was seen to increase with increasing temperature, showing little effect of the differences in time that the various cells had been under test.

0

20

40

60

80

100

120

140

160

0 5 10 15 20 25 30Time / days

Rel

ativ

e ca

paci

tanc

e / %

30°C50°C70°C80°C

Fig. 7. Effect of storage time at elevated temperatures on specific capacitance. Relative capacitance is calculated based upon time = 0 specific capacitance.

CONCLUSIONS

Birnessite MnO2 has been successfully made in a number of different morpholgies through variation of reaction conditions in a simple hydrothermal synthesis. Phase pure materials were obtained up to 140 ºC, with the manganite manganese oxyhydroxide phase also being formed at higher temperatures. A range of specific surface areas and pore volumes was observed, with the specific surface area generally increasing with increasing reaction time. An initial assessment of specific capacitance of the materials in hybrid supercapacitor cells with aqueous neutral electrolyte showed a variation between 40 and 105 F g-1. The 1203D material was chosen for study of key performance indicators at elevated temperatures. As the temperature was increased from 30 to 80 ºC, the specific capacitance was seen to increase by nearly 100%. Galvanostatic cycling at 2.5 A g-1 showed a loss of capacitance, becoming more significant as the

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temperature was increased; at 70 and 80 ºC, values after 1000 cycles were lower than those at the 30 and 50 ºC respectively. Furthermore, through investigation of the effect of elevated temperature storage of the devices, it was shown that the number of cycles performed under such conditions is not the sole factor determining the lifetime of such supercapacitors.

REFERENCES [1] B.E. Conway, Electrochemical Supercapacitors, Scientific Fundamental and Technological Applications, Kluwer Academic/Plenum, New York, 1999.

[2] Q. Wang, Z. Wen, and J. Li, “A hybrid supercapacitor fabricated with a carbon nanotube cathode and a TiO2-B nanowire anode,” Advanced Functional Materials 16, 2009, pp. 2141- 2146.

[3] G. Lota, K. Lota, and E. Frackowiak, “Nanotubes based composites rich in nitrogen for supercapacitor application,” Electrochemistry Communications 9 2007, pp. 1828-1832.

[4] A. Chandra, A.J. Roberts, E. Lam How Yee, and R.C.T. Slade, “Nanostructured oxides for energy storage applications in batteries and supercapacitors,” Pure and Applied Chemistry 81, 2009, pp. 1489-1498.

[5] J. Chmiola, Y. Yushin, Y. Gogotsi, C. Portet, P. Simon, and P.L. Taberna, “Anomalous Increase in Carbon Capacitance at Pore Sizes Less Than 1 Nanometer,” Science 313, 2006, pp. 1760-1763.

[6] A.K.C. Gallegos and M.E. Rincon, “Carbon nanofiber and PEDOT-PSS bilayer systems as electrodes for symmetric and asymmetric electrochemical capacitor cells,” Journal of Power Sources 162, 2006, pp. 743-747.

[7] E. Frackowiak, V. Khomemko, K. Jurewicz, K. Lota, and F. Beguin, “Supercapacitors based on conducting polymer/nanotubes composites,” Journal of Power Sources 153, 2006, pp. 413-418.

[8] C. Merino, P. Soto, E.V. Ortego, J.M.G.D. Salazar, F. Pico, and J.M. Rojo, “Carbon nanofibres and activated carbon nanofibres as electrodes in supercapacitors,” Carbon 43, 2005, pp. 551-557.

[9] H.Y. Lee and J.B. Goodenough, “Supercapacitor behavior with KCl electrolyte,” Journal of Solid State Chemistry 144, 1999, pp. 220-223.

[10] S.C. Pang, M.A. Anderson, and T. Chapman, “Novel electrode materials for thin-film ultracapacitors: Comparison of electrochemical properties of sol-gel-derived and electrodeposited manganese dioxide,” Journal of the Electrochemical Society 147, 2000, pp. 444-450.

[11] J. P. Zheng and T.R. Jow, “The limitations of energy density for electrochemical capacitors,” Journal of the Electrochemical Society 144, 1997, pp. 2026-2031.

[12] W. Sugimoto, K. Yokoshima, Y. Murakami, and Y. Takasu, “Charge Storage Mechanism of Nanostructured Anhydrous and Hydrous Ruthenium-Based Oxides,” Electrochimica Acta 52, 2006, pp. 1742-1748.

[13] B.E. Conway, V. Briss, and J. Wojtowicz, “The Role and Utilization of Pseudocapacitance for Energy Storage by Supercapacitors,” Journal of Power Sources 66, 1997, pp. 1-14.

[14] A.J. Roberts and R.C.T. Slade, “Effect of specific surface area on capacitance in asymmetric carbon/α-MnO2 supercapacitors,” Electrochimica Acta 55, 2010, pp. 7460-7469.

[15] A.J. Roberts and R.C.T. Slade, “Controlled synthesis of ε-MnO2 and its application in hybrid supercapacitor devices,” Journal of Materials Chemistry 20, 2010, pp. 3221-3226.

[16] S. Komaba, N. Kumagai, and S. Chiba, “Synthesis of Layered MnO2 by Calcination of KMnO4 for Rechargeable Lithium Battery Cathode,” Electrochimica Acta 46, 2000, pp. 31-37.

[17] X. Wang, X. Wang, W. Huang, P.J. Sebastian, and S. Gamboa, “Sol-gel template synthesis of highly ordered MnO2 nanowire arrays,” Journal of Power Sources 140, 2005, pp. 211-215.

[18] V. Subramanian, H. Zhu, and B. Wei, “Nanostructured MnO2: Hydrothermal Synthesis and electrochemical Properties as a Supercapacitor Electrode Material,” Journal of Power Sources 159, 2006, pp. 361-364.

[19] T. Brousse, M. Toupin, R. Dugas, L. Athouel, O.Crosnier, and D. Belanger, “Crystalline MnO2 as possible alternatives to amorphous compounds in electrochemical supercapacitors,” Journal of the Electrochemical Society 153, 2006, pp. A2171-A2180.

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[20] L. Tao, C.-G. Sun, M.-L. Fan, C.-J. Huang, H.-L. Wu, Z.-S. Chao, and H.-S. Zhai, “A redox-assisted supramolecular assembly of manganese oxide nanotube,” Materials Research Bulletin 41, 11, 1996, pp. 2035-2040.

[21] A.J. Roberts and R.C.T. Slade, “Birnessite nanotubes for electrochemical supercapacitor electrodes,” Energy & Environmental Science 4, 2011, pp. 2813-2817.

[22] K.S.W. Sing, D.H. Everett, R.A.W. Haul, L Moscou, R.A. Pierotti, J. Roquerol and T. Siemieniewska, “Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984),” Pure and Applied Chemistry 57, 1985, pp. 603-619.

[23] J. Rouquerol, D. Avnir, C.W. Fairbridge, D.H. Everett, J.H. Haynes, N. Pernicone, J. D. F. Ramsay, K.S.W. Sing, and K.K. Unger, “Recommendations for the characterization of porous solids (Technical Report),” Pure and Applied Chemistry 66, 1994, pp. 1739-1758.

BIOGRAPHICAL NOTE Conference presenter: Bob Slade is Professor of Energy Chemistry at the University of Surrey (25 miles from London, UK) and leads a team of 20+ researchers in sustainable electrochemical generation and storage of electrical energy. He

trained at the University of Oxford and has previously held posts in the UK at the Universities of York, Oxford, and Exeter. Current programs include pioneering work in alkaline membrane fuel cells, leadership of the UK consortium on biological fuel cells, strategic development of supercapacitors utilizing sustainable materials exhibiting pseudocapacitance, and a program in materials development and testing for redox flow batteries. He is the UK representative on the EuCheMS (European Association for Chemical and Molecular Sciences) working party on energy.

http://www.sciencedirect.com/science/article/pii/S0025540806001462?_alid=1797818158&_rdoc=8&_fmt=high&_origin=search&_docanchor=&_ct=12&_zone=rslt_list_item&md5=27fd1ed4ef9334740ebc481d743d57d6



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Poster Session 1

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A BATTERY STORAGE SYSTEM FOR DISTRIBUTED DEMAND RESPONSE IN RURAL ENVIRONMENTS

Roy McCann,1 Robert Winkelman,2 and David Moody2 1University of Arkansas, Fayetteville, AR, USA

2LGW, Inc., Fayetteville, AR, USA

Keywords: Battery storage, distributed energy, demand response, advanced metering infrastructure

This paper presents the results of deploying four

sets of 75-kWh battery distributed energy storage (BDES) systems developed by LGW Incorporated at residences located in Binger, Oklahoma, and Fayetteville, Arkansas. In addition, two commercial facility installations have been brought online. Each of the sites includes renewable energy generation consisting either of (1) solar photovoltaic: 450 watts at residential sites and 10 kilowatts (kW) at commercial sites, or (2) wind generation peak of 65 kW for a commercial facility. The BDES system was developed by LGW in collaboration with the University of Arkansas and deployed with assistance from Caddo Electric Cooperative (Oklahoma) and Ozarks Electric Cooperative (Arkansas). The motivation for this research is to investigate the potential benefits of implementing a distributed demand response (DDR) system that is configured for the circumstances encountered in rural environments. The objectives are to quantify the benefits of BDES systems in terms of

• Peak load management, • Electric service reliability, • Renewable integration, • Voltage regulation/Reactive power support,

and • Financial and economic incentives.

Challenges for rural electric power systems

include recurring outages due to storm damage, difficulty in voltage regulation, and large load fluctuations associated with agricultural equipment and irrigation systems over low-density networks covering large geographical areas. There has been considerable research in the integration of electric utility communication protocols with customers in real time to coordinate loads for peak shaving and load leveling [1]. The adoption of distributed energy sources has further encouraged the investigation of advanced demand response (DR) systems [2]. Much

of the published work in this area has been with respect to analysis of historical usage profiles [3]. The contribution of this pilot study is the development of a DDR system where an electric utility has the ability to schedule in 15-minute intervals the maximum load level for a particular customer. The BDES system is implemented with an IEEE 1547 compliant grid-tie power electronic inverter [4-5] and a 75-kWh lead-acid battery storage system that can meet customer demand for loads that exceed the utility DDR set point. Commands and feedback between the utility and the BDES system is over a Cooper-Cannon PowerLine communication link. Included in the BEM functionality is coordination with the utility service provider to signal preferred times for recharging the battery bank during off-peak times [6]. In this pilot, the four installation sites generally were operated with 12-kW discharge during the peak daily load times of 2:00 to 8:00 p.m. Battery charging occurred during off-peak time when marginal electricity rates are lowered. Operational data collected remotely from the LGW installation in Binger, Oklahoma, can be viewed at http://www.lgwenergynow.com/MSLineGraph.aspx on line with real-time updates.

A critical element to the success of the pilot study of the BDES systems is the battery technology. Lead-acid batteries were selected due to low cost and robustness to environmental conditions. By properly accounting for conditions at the site location, the battery configuration can be optimized to provide sufficient reserve capacity for the anticipated temperature and humidity variations. A novel battery formulation has been developed by the authors that increases the porosity of Pb/PbO2 plates beyond that achieved with conventional tribasic and tetrabasic lead oxides. Lead normally grows in needle-shaped crystals with secondary and tertiary branches. Novel curing and soaking processes have been found to produce octahedral and dodecahedron crystals that

http://www.lgwenergynow.com/MSLineGraph.aspx

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have both improved electrochemical porosity with high anode/cathode plate densities. This processing technology achieves approximately 16% increased reserve capacity for a given battery mass/volume metric. Lead-acid battery technologies are attractive economically because of the nature of lead mining production and processing. In particular, purified lead (Pb) ore is the principal capital investment in lead-acid battery systems. Given that reprocessing recovers over 98% of the Pb/PbO2 material, the capital investment in a lead-acid battery installation is a one-time expense that depending on commodity prices may in some cases become an investment for the battery diesel generator (DG) system. Consequently, the financing of lead(II) sulfate (PbSO4) batteries can be achieving in various means. One option would be for the DG system vendor to retain ownership of the Pb/PbO2 with lease options made to the utility company for use of the inverter and other related components. Alternatively, the utility may exercise an option to own the Pb/PbO2 material and provide the DG as part of a service contract. This arrangement overcomes one of the principal challenges in deploying DG systems in terms of the cost implications for utility and end users/customers wishing to employ energy storage systems.

In conclusion, it has been demonstrated that BDES systems are effective in providing improved reliability and load management capability in meeting utility DDR objectives. In addition, BDES systems confirm the capability for financial planning [7] by the associated electric utility company for postponing the need for adding generation capacity and therefore avoiding large capital expenditures.

REFERENCES [1] S. Widergren, “Demand or Request: Will Load Behave?,” Proceedings of the 2009 IEEE Power and Energy Society General Meeting, 2009.

[2] F. Rahimi and A. Ipakchi, “Demand Response as a Market Resource Under the Smart Grid Paradigm,” IEEE Transactions on Smart Grid 1, 2010, pp. 82-88.

[3] G. Abrate and D. Benintendi, “Measuring the potential value of demand response using historical market data,” Proceedings of the 6th International IEEE Conference on the European Energy Market, 2009.

[4] B. Kroposki, C. Pink, R. DeBlasio, H. Thomas, M. Simões, and P.K. Sen, “Benefits of Power Electronic Interfaces for Distributed Energy

Systems,” IEEE Transactions on Energy Conversion, vol. 25, no. 3, 2010, pp. 901-908.

[5] A. Huang, M. Crow, G. Heydt, J. Zheng, and S. Dale, “The Future Renewable Electric Energy Delivery and Management (FREEDM) System: The Energy Internet,” Proceedings of the IEEE, vol. 99, no. 1, 2011, pp. 133-148.

[6] T. Senjyu, Y. Miyazato, A. Yona, N. Urasaki, and T. Funabashi, “Optimal Distribution Voltage Control and Coordination With Distributed Generation,” IEEE Transactions on Power Delivery, vol. 23, no. 2, 2008, pp. 1236-1242.

[7] A. Gil and G. Joos, “Models for Quantifying the Economic Benefits of Distributed Generation,” IEEE Transactions on Power Systems, vol. 23, no. 2, 2008, pp. 327-335.

BIOGRAPHICAL NOTES Conference presenter: Roy McCann received a B.S. in Electrical Engineering from the University of Illinois at Urbana-Champaign in 1990 and an M.S. in Electrical Engineering for the University of Illinois at Urbana-Champaign in 1991. After completing the MSEE degree, he was

employed by General Motors Corporation in Dayton, Ohio, working towards the development of advanced electronically controlled engine, braking, and steering systems. He began a Ph.D. program at the University of Dayton in 1995 related to electric power systems research. With funding by Delphi Corporation and the Dayton Area Graduate Studies Institute, he was awarded the Ph.D. in Electrical Engineering in 2001 from the University of Dayton. During this time, Dr. McCann was the engineering supervisor for the Electrical Systems Group at Delphi-Saginaw Steering, where the first large-scale fully electric and electronically controlled power steering system was designed and produced for the North American passenger vehicle market. Dr. McCann has received 19 U.S. patents related to his work in automotive electronic systems and authored numerous papers for the Society of Automotive Engineers (SAE) and the IEEE. In August 2003, Dr. McCann accepted an appointment as an Associate Professor of Electrical Engineering at the University of Arkansas–Fayetteville. In August 2009, Dr. McCann was promoted to the rank of Professor. He teaches and conducts research in control systems with particular emphasis on energy conversion related applications. He is the director of the Control Systems laboratory

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at the University of Arkansas and also an associate director for the National Center for Reliable Electric Power Transmission (NCREPT), also located at the University of Arkansas.

Robert Winkelman has served as Chief Executive Officer of LGWI since the company was formed in 2009. He earned an LLB degree from the University of Texas. He was a trial lawyer for Baker, Botts, Andrews & Shepherd in Houston until joining one of his principal

clients, Electric Storage Battery Company (ESP). ESP later became Exide, the world's largest battery manufacturer with 26 factories worldwide. He worked with research and development at Exide developing an electric car that was successfully marketed in the United States under the name Sebring City Car. He subsequently earned national awards for his work with Sears on the development of the Diehard battery. He left Exide to form Winkelman Battery Company, which became the largest American importer of Global Y batteries from South Korea. He also worked with a leading Chinese battery manufacturing company named Palma to develop an advanced version of an absorbed glass mat (AGM) battery. Finally, he was a principal and early contributor to Good Earth Energy Conservation, Inc., an electric vehicle manufacturer, before forming LGWI. His reputation as a leader in battery technology, energy management, and electric vehicle development has resulted in a number of international consulting assignments, including projects in China, Russia, Bulgaria, Hungary, Zanzibar, and South Africa.

David Moody joined the company in February 2011 and currently serves as President of LGWI. He has degrees in Public Administration from the University of Central Arkansas (Honors) and the University of Houston. He joined the federal service through the Presidential

Management Internship Program and worked for the National Aeronautics and Space Administration and in the aerospace industry for 14 years. During that time he served as a program analyst, manager, and consultant for the shuttle, space lab, and space station programs. Since leaving the aerospace industry, Mr. Moody has owned and operated several businesses in the fields of risk management, retail, and business consulting. As a business consultant focused on startup and technology businesses, he has worked with a variety companies to commercialize products and services in the areas of nanotechnology, biotechnology, medical devices, computer science, and energy technology. Before joining LGWI, Mr. Moody served as the Deputy Director of the Arkansas Energy Office. As Deputy Director he was responsible for developing the staff and organization to administer $52M in federal grants that funded 13 major programs and dozens of individual projects across Arkansas.


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THE STATE/FEDERAL ENERGY STORAGE TECHNOLOGY ADVANCEMENT PARTNERSHIP PROJECT

Anne Margolis

Clean Energy States Alliance, 50 State Street, Montpelier, VT, USA

ABSTRACT The Energy Storage Technology Advancement Partnership (ESTAP) is a new federal-state funding and

information-sharing project that aims to accelerate the deployment of energy storage technologies in the United States. The value proposition for participating states is to work closely with the U.S. Department of Energy (DOE) on near-term joint funding and technology deployment, to join a network of leading states supporting energy storage technology, and to achieve faster progress in energy storage commercialization and economic development.

BACKGROUND Energy storage has the potential to provide

significant support to the integration of renewable energy in the United States. However, public funding and support are critical to accelerate progress and achieve cost reductions and widespread deployment for these technologies, including batteries, flywheels, thermal storage, aboveground compressed air, micro-pumped hydro, and others.

The DOE and Sandia National Laboratories (SNL) are interested in accelerating the pace of deployment of energy storage technologies through a cooperative partnership with interested states. The Clean Energy States Alliance (CESA) has been asked to establish and facilitate this state-federal energy storage technology advancement partnership project. The initiative is funded by SNL and implemented in cooperation with the DOE Office of Electricity Delivery and Energy Reliability (OE).

PROJECT PURPOSE The project’s overall purpose is to create a new

federal and state partnership focused on energy storage technologies with joint funding and coordination to accelerate energy storage technology commercialization and deployment.

PROJECT OBJECTIVE The project’s objective is to accelerate the pace

of deployment of energy storage technologies in the United States through the creation of a technical assistance and co-funding partnership between the states and the DOE.

PROJECT ACTIVITIES • Creation of a State Energy Storage Network

and a Stakeholder Network • Information Sharing Webinars and Meetings • State and Stakeholder Surveys • Creation of DOE-State Memoranda of

Understanding • Joint Project Funding Framework and

Solicitation for Project Deployment

HOW TO PARTICIPATE Interested state and other entities administering

public funds for clean energy projects that are willing to consider committing some funding to and participating in the DOE-State partnership to support energy projects are invited to join the State Energy Storage Network. Members of this network will help develop recommendations for implementing the funding partnership and a structure for advancing cooperation and information sharing. Other interested stakeholders, including manufacturers, universities, and utilities, and other end users within states are encouraged to participate in conjunction with state agencies.

• Funding level and time frame. State Energy Storage Network members are asked to use their best efforts to identify and seek state-based funding to contribute to the DOE funding opportunity to advance energy storage technology deployment. Because of state-specific procurement policies, restrictions, and requirements, there may be several different approaches used and

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tailored to participating states to accommodate broad participation in the cooperative arrangement with DOE. There is no required funding amount to participate. However, states are strongly encouraged to consider providing at least a funding level of $1 million to leverage matching DOE energy storage cost-share support in the 2011-2012 time frame. States will retain full discretion to apply state-specific criteria to any projects where state funding is awarded as a cost share.

• Timeline. During the spring, summer, and

fall of 2011, the Project Team will be meeting individually with interested states to discuss and agree on the details of the co-funding arrangement, including clarifying state interests, priorities, and questions. Then, interested states will meet as a group in late 2011 to review and attempt to finalize a project selection process and cost-sharing arrangements with the DOE.

Interested states are invited to participate by

contacting CESA’s project director, Anne Margolis ([email protected] or 802.223.2554). Additional information is available on the ESTAP page at www.cleanenergystates.org.

BIOGRAPHICAL NOTE Conference presenter: Anne Margolis is a Project Director for the Clean Energy States Alliance (CESA), where she focuses primarily on member services as well as outreach and communication efforts to members and external stakeholders, including creation of print and web content. She directs the Energy Storage and Technology Advancement Partnership (ESTAP) and also co-directs the CESA Solar and the Wind Siting & Acceptance Projects, as well as managing CESA's State Leadership in Clean Energy (SLICE) awards program. Before joining CESA, Ms. Margolis was the Director of the Vermont Clean Energy Development Fund. She holds a B.A. degree in Environmental Studies from Dartmouth College.


http://www.cleanenergystates.org/

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APPLYING RENEWABLE STORAGE TO THE COMMERCIAL ENVIRONMENT

Jeff Hires, P.E.

GS Battery (USA) Inc., Roswell, GA, USA

ABSTRACT

This poster will highlight the details of two recent projects GSB (GS Battery [USA] Inc.) has been involved in that combine renewable energy (photovoltaic energy in these cases) and battery storage in commercial environments. These projects were implemented to demonstrate the real-world benefits (electrical and economical) of coupling advanced battery storage technology with renewable energy technology.

The first project was installed at Mesa del Sol in Albuquerque, New Mexico, in a commercial office building. The Mesa del Sol (MdS) project is one of the first projects in the United States that is a part of the five-year cooperative research agreement between Sandia National Laboratories (SNL) and Forest City (MdS developer). Beginning in April 2009, this agreement was set up to complement the SNL Distributed Energy Technical Lab (DETL) to provide the Department of Energy (DOE) a way to provide the public data from real-world installations. The project funding was managed by SNL with a $2 million earmark that Forest City received. The MdS project includes a grid-tied PV/battery storage system including 17.1-kilowatt (kW) photovoltaic (PV) modules, 15-kW PV/battery power electronics, and 20.48-kWh advanced valve-regulated lead-acid (VRLA) battery technology. The battery technology used at this site includes design features such as glass fiber tubular positive plates, nano-carbon applied to negative plates, and advanced granular silica gel. These features combined together create a battery with higher charge efficiency and increased cycle life and operating years, even in a high-temperature condition. Storage benefits that are being demonstrated at the site include time of use (TOU) energy cost management and renewable energy time-shift. The collected storage benefit data will be shown on this poster.

The second project was installed at the GSB main office building in Roswell, Georgia. This project was funded by GSB to provide an on-site demonstration of the electrical and economic benefits of PV plus storage at a typical commercial office building. The system consists of 37.44-kW PV modules, 30-kW PV inverter, 15-kW battery inverter, and 144-kilowatt hour (kWh)

battery storage. The battery technology used at this site is similar to the battery technology used at the MdS site. Storage benefits including TOU energy cost management and electric service and reliability uninterruptible power supply are being demonstrated at this site and such data will be shown on this poster. This project was the first commercial PV installation with energy storage in the state of Georgia.

In conclusion, GSB believes that these two projects will be good examples of typical commercial renewable storage installations and will provide meaningful, real-world data that can be used to validate some of the many benefits of renewable storage.

BIOGRAPHICAL NOTE Mr. Hires joined GS Battery in 2010 and currently serves as Engineering Manager. Mr. Hires graduated from the University of Florida with a B.S. in Electrical Engineering in 2004. Mr. Hires is a registered professional engineer (electrical) with over 9 years

experience. Before coming to the GS Battery, he worked as a design engineer for a MEP consulting firm, where he worked on the electrical power and telecommunication designs of industrial, healthcare, institutional, and commercial buildings. In the last few years as a consulting engineer, he focused on the design of the many renewable energy projects (wind, photovoltaic, with and without battery storage). Since joining GS Battery, he continues to help design and implement many PV-plus and storage projects as well as storage-only projects around the country, as well as assisting our Japanese engineering team in the development and support of new and existing products.

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79

RECENT U.S. POLICY AND LEGAL IMPLICATIONS FOR ENERGY STORAGE VIS-À-VIS RPS MANDATES

Jacquelynne Hernández

Sandia National Laboratories, New Mexico, USA

ABSTRACT The fast-approaching implementation dates for United States Renewable Portfolio Standards (RPS) accelerate

the need for a clear energy storage federal policy. Further, the evolution from a vertical electricity delivery system to a market-based design structure and the technical challenges to transform the existing system to the next-generation smart grid require large-scale energy storage installations. However, energy storage at the utility level has a multiple personality. For, depending on its application, commercial, megawatt-scale energy storage devices can provide generation support, transmission and distribution asset deferral, or supply ancillary services as a market function. Each of these roles for energy storage brings with it legal and policy questions.

Keywords/phrases: RPS, grid-connected, energy storage, policy, market design

INTRODUCTION

In the United States, 29 states and the District of Columbia have adopted a Renewable Portfolio Standard, or RPS. A typical RPS requires an increase in renewable energy resources that involve wind, solar, and geothermal technologies. Just as the type energy of source may vary, so do the full implementation dates. The RPS is at the state level; thus there are several layers of complexity:

(1) There is not a U.S. federal policy for RPS; (2) The regulations for RPS (about 40% of U.S.

electricity sales) vary from state to state or are non-existent;

(3) Importing Variable Energy Resources (VERs) into the grid affects reliability;

(4) Energy storage was not specifically written into the legislation for RPS; and

(5) There are environmental and market policies that affect the use of electrical energy storage at the federal, state, and local levels.

BACKGROUND

The U.S. Federal Energy Regulatory Commission (FERC) is responsible for regulating interstate transmission of electricity, natural gas, and oil. As part of its duty to the consumer, the FERC provides standards to protect the reliability of high-voltage interstate transmission and monitors energy markets.

As recently as February 2011, FERC issued a Notice of Proposed Rulemaking that would require each of the grid operators under its jurisdiction to structure their regulation market tariffs to provide pay-for-performance (PFP). Grid operators would require implementing a pricing structure that pays faster ramping resources a higher price for their service. This, of course, implies use of energy storage technologies like the flywheel.

If adopted, then the PFP becomes a FERC market policy that will reward specific storage technology. The issue is that yet other policy positions have to be adopted for VERs, energy efficiency goals, and RPSs to be effective. The issue is that the energy storage industry perhaps has not clearly communicated the following:

• Energy storage is NOT a product. • Liability issues specific to certain energy storage

technologies hamper implementation (i.e., Compressed Air Energy Storage [CAES]).

• Energy storage is an enabling technology that has legal implications for adding renewable resources to both transmission and distribution systems.

PROBLEM

Electric power dispatchers manage variable, intermittent renewable energy sources by maintaining sufficient spinning reserves, adding automatic generation in fast-responding combustion turbines, or

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upgrading ramping rates. These technology applications represent temporary patchwork solutions. Deeper electric grid penetration of renewable resources will require energy storage for rapid dispatch and reliability. There are ten (10) pumped storage plants and a single CAES facility in the United States, and only one state that has written legislation to satisfy RPS targets [California AB2514] [1]. Even without RPS mandates, the many roles that advanced energy storage applications and technologies can play require an update of energy policy.

DISCUSSION The Energy Storage Council (ESC) defines five

distinct elements of the electric power market: fuel or energy sources, generation, transmission and marketing, distribution support, and energy services [2]. Energy storage can easily be an integrator of the existing market segments for conventional and renewable resources to create a more responsive market, and energy storage can also aid in technical challenges.

Energy Storage as Generation Support

Harvesting storage of bulk energy during low demand (at night) then using the commodity in the daytime can satisfy peak demand on any given system. This approach permits arbitrage of both the production price of both demand periods as well as a uniform load factor for generation (and possibly also transmission and distribution [T&D] systems). Further, when coupled with VERS, energy storage can represent baseload generation support; thus it has a dual role as generator and purchaser in an RPS arrangement.

Storage as Transmission and Marketing

Conditions on the power grid constantly change as loads change or as disruptions occur across the network (for wholesale power). Utilities ramp power plants up or down second by second to follow the load. Timing and access for loads help to account for congestion on the transmission system, which may require an expense to utilities that have to use stabilizing equipment. Requirements associated with the smart grid and use of renewable resources introduces even more stability issues. Energy storage is a viable resource for generation and transmission facilities for increased demand as well as for asset upgrade deferral.

The American Electric Power (AEP) company wanted to add a battery storage system into its system upgrade in Texas that has huge wind resources. AEP requested that the energy storage device be treated as a transmission facility (and therefore eligible for cost recovery through regulated transmission rates) and not as an energy market participant [3]. The Public Utility Commission (PUC) of Texas permitted AEP’s battery as a transmission facility, with FERC’s blessing.

Western Grid Development got FERC’s approval for a similar request but under protest from CAISO [4], who would have to include the project as part of its Independent System Operator (ISO) regional planning process.

Storage and Ancillary Services

Regulation power consists of short spikes of power supplied when the grid is destabilized due to sudden increases in demand. Batteries are ideal to provide a stabilizing function, with small amounts of power. PJM uses lithium-ion batteries for regulation power. As early as 2009, the PJM interconnect operators demonstrated that transmission networks should be permitted to employ batteries to improve grid stability and reliability by balancing variations in their load.

A utility can become caught up in the current policy requirement that compels third-party sellers of ancillary services to prove in a formal study that they lack market power before being permitted to sell their services at market-based rates [5]. Other ancillary services that storage can support include asset deferral, contingency service, black start, voltage regulation, and area control. Here the term area control is defined as the prevention of unplanned transfer of power between one utility area and another.

SUMMARY Energy storage can play several roles in the

vertical electricity delivery system: generation support, transmission, or bulk distribution at the utility level. As a market function, storage can be part of a system’s energy management, bridging power, or as an ancillary service providing operator’s tools to ensure power quality, reliability, or stability. The challenges of grid integration of renewable energy sources from the U.S. RPS mandates have brought to light a need to address legislative, regulatory, economic, and technical requirements related to energy storage.

Policy is the tool to advance technical challenges like integration of renewable energy sources into the existing grid. Energy storage is the catalyst to drive business models for electric power market strategies. But it is the group of subject matter experts who serve as resources to connect the dots for the end user and stakeholder to understand the many applications of energy storage for the next-generation (smarter) grid.

RECOMMENDATIONS Energy storage experts, system operators, utility

managers, and other stakeholders can work together to develop policy positions and propose industry standards that define the boundaries of energy storage – in particular regulated functionality versus a market functionality.

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CONCLUSIONS Whether the energy sources are conventional or

renewable, federal regulators and state utility asset owners must take a position to improve current policy to complement emerging energy storage technologies and applications to help move market design forward.

REFERENCES [1] California Legislature – 2009-10 Assembly Bill Number 2514, “An Act to Amend Section 25302 of the Public Resources Code, and to Amend Sections 454.3. 9615, and 9620 of, and add Chapter 7.7 to Part 2 of Division 1 of, the Public Utilities Code, Relating to Energy (Storage),” Proposed by Nancy Skinner, approved by the California Legislature on June 21, 2010, and signed into law by Governor Arnold Schwarzenegger on September 29, 2010.

AB 2514 will mandate storage equal to 2.25% of daytime peak power by 2014 and 5% of daytime peak power by 2020. The bill would additionally require each electrical corporation and local publicly owned electric utility, commencing January 1, 2011, to implement a 5-year program to employ distributed thermal, mechanical, or electrochemical energy storage systems to maximize shifting of electricity use for air-conditioning and refrigeration from peak demand periods to offpeak periods. The bill would require each electrical corporation and local publicly owned electric utility to develop energy storage plans to meet the energy storage portfolio procurement requirements and to report certain information to the Energy Commission.

[2] Energy Storage Council, “Energy Storage – The Missing Link in the Electricity Value Chain,” May 2002, at www.energystoragecouncil.org.

[3] M. Giberson, M “Energy Storage on the Grid: Transmission Equipment or Market Participant?,” January 2010, at http://www.knowledgeproblem.com

[4] D. McMillan et al., “The Regulatory Challenge of Energy Storage,” March 10, 2010, at

.

http://sedc-coalition.eu/wp-content/uploads/2011/06/MW-Storage-Farms-10-04-10-Storage-Costs.pdf

[5] 135 FERC 61,240, United States of America Federal Energy Regulatory Commission, 18 CFR Chapter I [Docket Nos. RM11-24-000 and AD10-13-000], “Third-Party Provision of Ancillary Services; Accounting and Financial Reporting for New Electric Storage Technologies,” June 16, 2011.

.

Secondary Resources

D. Divine, “Getting to 33% RPS Through Comprehensive State-wide Grid Planning: A Revised Straw Proposal,” Eagle Crest Energy Company, Inc., November 13, 2009.

L.R. Evers, “FERC Seeks Comments on Energy Storage and Ancillary Services,” in Smart Grid Legislation News, June 22, 2011.

R. Fioravanti, “Energy Storage: Can it Replace Transmission?,” August 31, 2010, at www.smartgridnews.com

R. Fioravanti, “Energy Storage: Making it Work with Generation Applications,” August 3, 2010, at

.

www.smartgirdnews.com

News Analysis, U.S. Senate Gets Smart About Energy Storage with Tax Credit Legislation, July 21, 2010, “The Storage Technology of Renewable and Green Energy Act of 2010 (STORAGE 2010); Legislation proposed by U.S Senator Jeff Bingaman (D-NM), U.S. Senator Ron Wyden (D-OR), and U.S. Senator Jeanne Shaneen (D-NH).

.

R. Peltier, “Energy Storage Enables Just-in-Time Generation,” in Power Magazine, April 1, 2011.

BIOGRAPHICAL NOTE Jacquelynne Hernandez, Member of Technical Staff at Sandia National Laboratories (SNL), is in the Energy Systems Analysis group.

Education: BSEET (focus area: Power Electronics) from DeVry

Institute of Technology in Decatur, Georgia; BSEE – University of New Mexico, MSEE – New Mexico State University – Power Engineering, part of the Electric Utilities Management Program.

Ms. Hernandez’s work at SNL varies in topic, scope, and responsibility. It includes work in the Joint Test Assembly division that required use of her background in digital signal processing, telemetry designs, and assistance in running a ground station. Other assignments were as the Environment, Safety, and Health Coordinator for work in Papua, New Guinea’s, meteorological station and work in Alaska for the Arctic Radiation Measurement in Barrow, on the North Slope. She was part of the mission-level planning and submission configuration of software and hardware, and a radiation subject matter expert for single-event upset calculations for space vehicles in Satellite and Monitoring planning. Recent Power Engineering work involves Hawaii for Renewable Energy Grid Integration Systems (REGIS) and similar clean energy initiatives that require interpretation of state-specific energy policy, and the Middle East/South Asia International Programs that assist with exploring renewable energy technology options and policies in Non-Proliferation discussions. Energy policy assignments include work with the oil and gas industry for the transportation sector and SNL’s national energy-water nexus roadmap.

http://www.energystoragecouncil.org/

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USE OF STORAGE TO MITIGATE FREQUENCY VARIATIONS IN A LOAD FREQUENCY CONTROL MODEL

Michelle Lim, Mohit Chhabra, and Prof. Frank Barnes

Electrical Computer and Energy Engineering Department, University of Colorado at Boulder, Boulder, CO, USA

The increase of renewable and intermittent

energy sources replacing more stable and conventional sources such as gas-fired or coal plants in the power grid could lead to large frequency variations, sometimes exceeding that of grid limits (±1 Hertz [Hz] of 60 Hz). These limits are to ensure proper operation of induction generators and also to limit losses in power system components like transformers.

Using a load-frequency control model [1] with the assumption that load-frequency and reactive-voltage stability parts are decoupled [2], it can be shown that the use of specific storage devices (with individual time constants and duration of storage) reduces excessive frequency variations due to renewable energy.

We look at a simple system with four different sources of power: (a) a gas-fired plant servicing as the frequency leader, (b) a wind-powered system, (c) a short-term storage unit to smooth wind variation (battery type), and (d) a long-term storage unit as a reserve plant (constant-speed hydro plant). The short-term storage plant responds to the variations of wind within a few 60-Hz cycles (designated as the storage response time); however, the long-term storage plant is assumed to have a lead time of about 5 to 10 minutes.

Table 1. Storage description.

Type of Generation

Rated Power (MW)

Duration of Discharge

Gas-Fired Plant 300 Months

Wind System 250 (max) Intermittent Short-Term

Storage 90 3-4 minutes

Long-Term Storage 120 3 hours to

days

The simulated wind system is assumed to have a maximum rated power of 250 megawatts (MW). Simulations done are for wind energy (megawatt hour [MWh]) penetration levels ranging from 10% to 40% of the overall load energy of ~90 MWh.

A sodium sulfur (NaS) battery connected to a wind farm in Minnesota has been used effectively for wind leveling and smoothing operations. Using a model of this NaS battery as short-term storage, frequency variations due to variability of renewable energy have been observed to decrease due to a wind-smoothing operation.

Figure 1(a) shows frequency variations of a system without any energy storage devices. Figure 1(b) shows corresponding frequency variations of a power system with the NaS battery model for a wind-smoothing operation.

Fig. 1a (right) and 1b (left). Frequency variations.

0 2 4 6 8 10 12 14 16 18 20 22 24 2658

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60

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Time (min)

Fre

quen

cy (H

z)

Frequency Variations due to Intermittent Wind Power without Energy Storage

0 2 4 6 8 10 12 14 16 18 20 22 24 2658

59

60

61

62

Time (min)

Freq

uenc

y (H

z)

Frequency Variations due to Intermittent Wind Power and Smart Energy Storage

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This study found that:

(1) Different response times of various storage devices could lead to an increase (or decrease) of frequency variations with other parameters held constant. It is observed that the transients due to the switching in/out of storage devices could resonate with other components of the grid, thus leading to sharp increases in frequency deviations.

(2) Without any storage devices, the frequency changes are almost proportionate to the size and power profile of the intermittent power penetration. This result is shown assuming that there are no load changes in the system. The main reason for this assumption is to show that with just variability in renewable energy, large frequency deviations could be observed in the power grid.

(3) Differing time constants of the various interacting power sources (i.e., wind, gas-fired plant, and energy storage) could lead to an unstable system.

(4) The selection of a proper speed-droop characteristic plays an important role. At very small speed-droop values, undamped oscillating frequency deviations with increasing magnitude are observed [3, 4].

(5) Peak-power tracking must not induce power oscillations due to a searching algorithm for finding the maximum power point.

(6) Sufficient power capability of a transmission line plays an important role and is assumed in this model to be true.

REFERENCES

[1] A.J. Wood and B.F. Wollenberg, Power Generation Operation and Control, John Wiley & Sons: New York, 1996.

[2] L. Basanez, J. Riera, and J. Ayza, “Modelling and simulation of multiarea power system load-frequency control,” Mathematics and Computers in Simulation XXVI, 1984.

[3] E.F. Fuchs and M.A.S. Masoum, Power Conversion of Energy Renewable Systems, Springer: New York, April 2011.

[4] E.F. Fuchs and M.A.S. Masoum, Power Quality in Power Systems and Electrical Machines, Elsevier/Academic Press, February 2008.

BIOGRAPHICAL NOTES Conference presenter: Michelle Lim received a B.S. degree in aerospace engineering and an M.S. in electrical engineering from Wichita State University in 2006 and 2009, respectively. She has worked on the economic

feasibility of integrating wind energy in the state of Kansas with a Department of Energy grant in 2009. She has also worked at the National Institute for Aviation Research and Bombardier-Learjet Inc. in Wichita, Kansas. Currently, she is an electrical engineering Ph.D. candidate at the University of Colorado at Boulder.

Mohit Chhabra received a B.S. degree in electrical engineering from Western Michigan University, Kalamazoo, and an M.S. in electrical engineering from the University of Virginia, Charlottesville. As part of his graduate thesis, he simulated and

implemented PID and LQR control algorithms on a magnetic bearing based test machine. Previously, he worked as a controls engineer with SPX Corporation in Riverside, Michigan, working on the control and safety aspects of large-scale heat treat machines. He is working towards his Ph.D., and currently holds the position of Research Associate in the Renewable Energy for the Grid research group at the University of Colorado at Boulder.

Frank Barnes received his B.S. from Princeton University in electrical engineering in 1954 and his M.S. Engineer and Ph.D. from Stanford University in 1955, 1956, and 1958. He joined the University of Colorado in 1959. He was appointed a Distinguished

Professor in 1997. He was elected to the National Academy of Engineering in 2001 and received the Gordon Prize 2004 for innovations in Engineering Education from the National Academy. He is a fellow of IEEE, AAAS, and ICA and served as Vice President of IEEE for publication and as Chairman of the Electron Device Society. In the last four years he has been working on energy storage and the integration of wind and solar energy into the grid and the effects of electric and magnetic fields on biological systems.

Session 4 – EES Electrochemistry

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EXPLORATION AND PRACTICE OF ENERGY STORAGE TECHNOLOGY IN SHANGHAI

Zhang Yu: Senior Engineer

Technology and Development Center of Shanghai Municipal Electrical Power Company No. 310 of South Chongqing Road, 200025, Shanghai, People’s Republic of China

Energy storage system technology plays an important role in smart grid. Analyzing from the view of existing status and problems faced by the Shanghai grid, the article puts forward the necessity of applying energy storage technology in a large urban grid and the achievements in the key technologies in the Shanghai grid. As a comprehensive demonstration base for the pilot project of the smart grid in Expo 2010 by the State Grid (SGCC), the Shanghai Caoxi Energy Conversion Exhibit Station is also introduced in detail.

By the end of 2009, Shanghai Municipal Electric Power Company (SMEPC) possessed 16.5766 gigawatts (GW) in generation capacity and 101.5547-GVA transformer capacity in 815 substations between 35 kilovolts (kV) and 500 kV, with the annual power generation of 78.270 terawatt hours (TWh) and annual power sales of 91.760 TWh (see Figure 1).

As a grid operator of a typical mega-metropolis, SMEPC encounters three primary challenges:

• Soaring load, large peak-valley difference, and high pressure in grid construction and peak load regulating;

• Rapid development of renewable energy; and • Stricter requirements imposed on electricity

quality.

The core technology of energy storage is a front-edge technology with strategic influences and is in urgent need for the power grid development. State Grid Corporation of China (SGCC) has set up special projects for major scientific and technical innovation of energy conversion and assigned SMEPC a project of Development and Application of Stationary Battery Storage System for Large Urban Grids.

Fig. 1. Distribution of energy storage systems in the Shanghai grid.

After three years of hard work, a series of

substantial achievements has been made.

• Research and development of the Battery Energy Storage System (BESS)

On May 28, 2007, a base for the research of NAS

battery was set up jointly by SMEPC and the Shanghai Institute of Ceramics, Chinese Academy of Sciences, complying with the principle of “entity-mode operation, project-oriented management and industrialization preparation,” and mainly committed to the research on NAS batteries, cell modules, stationary batteries, and its monitoring system. In May 2010, the 100-kilowatt (kW) NAS BESS was put into grid-connected operation.

• Demonstration of the BESS

To demonstrate the achievements made by SGCC in energy storage in a large urban grid and in electric vehicle energy supply, SMEPC has embarked on building Caoxi Energy Conversion Comprehensive Demonstration Base since the end of 2009, which is one of the nine comprehensive demonstration projects of the smart grid for the Shanghai Expo by SGCC.

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An energy storage station, which is the first connected to the utility grid for demonstrative operation in the country, is built in the base with different kinds of energy storage subsystems amounting to 300 kW and remote-monitoring energy storage subsystems totaling 110 kW, in which the mode of distributed storage, concentrated monitoring, and unified dispatch is realized through a management system.

The goals of demonstrating the hundred-kilowatt-class energy storage system over the duration of the Shanghai Expo have been achieved by SMEPC. Next, the company will ultimately aim at popularizing the application of megawatt-class energy storage systems in the urban grid to obtain the independent intellectual property rights of the stationary BESS for large urban grids and make positive contributions to the development of domestic energy storage technology and the promotion of large energy storage stationary batteries.

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APPLYING A VARIETY OF BATTERY CHEMISTRIES FOR ENERGY STORAGE

Brad Roberts and Troy Miller

S & C Electric, 5251 W. Franklin Drive, Franklin, WI, USA

More battery chemistries are now being used for

energy storage in utility applications. This presentation will cover a variety of applications, including the Department of Energy (DOE) and Public Service of New Mexico (PNM) project that deployed a 1-MW storage system using advanced lead acid and ultra batteries as a storage management system (SMS) for a variety of grid support purposes. These purposes include:

(1) To mitigate substation overloads and defer major capital expenditures through peak shaving, making an emergency condition manageable within normal procurement and construction time frames;

(2) For general grid support functions (amps, volts, volt amperes reactive [VARs]);

(3) To improve customer reliability by serving distribution feeder loads (if a permanent fault “islands” a problematic feeder where the battery has been applied; and

(4) To study the storage of and ability to dispatch energy collected from intermittent sources (wind, solar, etc.).

This paper will focus on the PNM installation

using the ultra battery, but will also cover additional grid scale (>1 MW) storage projects that are being installed using lithium-ion, sodium-nickel, and sodium-sulfur batteries.

BIOGRAPHICAL NOTE Conference presenter: Bradford P. (Brad) Roberts, S&C Electric Company, Power Quality Systems Division Director.

Brad Roberts is the Power Quality Systems Director for the Power

Quality Products Division of S&C Electric Company, which specializes in low- and medium-voltage power protection systems.

Mr. Roberts has over 35 years experience in the design and operation of critical power systems, ranging from single-phase uninterruptible power supply (UPS) systems to medium-voltage applications. He began his engineering work as a systems reliability engineer in the Apollo Lunar Module Program at Cape Kennedy. He held senior management positions in two of the major UPS manufacturers during his career. He is a senior member of the Institute of Electrical and Electronics Engineers (IEEE) and has published over 40 technical papers and journal articles on critical power system design and energy storage technology.

Mr. Roberts is a registered professional engineer and has a B.S. in Electrical Engineering from the University of Florida. He is past chairman of the IEEE Power Engineering Society’s Emerging Technologies Committee and Executive Director of the Electricity Storage Association (ESA) and past chairman of the board. He has been a member of the ESA Board for 10 years. Mr. Roberts is a member of the U.S. Department of Energy Electricity Advisory Committee and Chairman of the Energy Storage Subcommittee.

Mr. Roberts is the 2004 recipient of the John Mungenast International Power Quality Award.

Troy Miller is a Business Development Manager in the Power Quality Products Division at S&C Electric Company. He has over 21 years of experience in the power engineering industry, including at Magnetek, Jefferson Electric, and ABB Inc,. Mr. Miller has a vast history in the application and implementation of all aspects of power electronics and power quality. Mr. Miller is a speaker at industry events for new product introductions and economic benefit analysis. He is currently responsible for power quality activities for S&C Electric, including Energy Storage, VAR compensation, and Uninterruptible Power Systems.

Mr. Miller received his B.S. in Electrical Engineering from the Milwaukee School of Engineering in 1993.

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MetILs: A FAMILY OF METAL IONIC LIQUIDS FOR REDOX FLOW BATTERIES

Travis M. Anderson,1 Harry D. Pratt III,1 Jonathan C. Leonard,1 Chad L. Staiger,2 and David Ingersoll1

1Advanced Power Sources Research and Development, Sandia National Laboratories, Albuquerque NM, USA

2Materials, Devices, and Energy Technologies,

Sandia National Laboratories, Albuquerque NM, USA

ABSTRACT We present a new family of metal ionic liquids that are synthesized in a single-step reaction from low-cost

precursors. The compounds consist of either manganese, iron, cobalt, nickel, copper, zinc, or cerium coordination cations and weakly coordinating anions such as 2-ethylhexanoate, triflate, triflimide, or tetrafluoroborate that may simultaneously act as a solvent and catholyte or anolyte. The results presented highlight the fundamental chemical concepts behind the formation of the materials as well as focus on our systematic improvements in viscosity, conductivity, and electrochemical reversibility.

Keywords: ionic liquid, flow battery, high energy density, low-cost energy storage

INTRODUCTION

Global energy consumption is projected to significantly increase by mid-century, and this increased need will be partially met through the use of renewable energy sources. Due to the intermittent nature of these resources, compatible large-scale energy storage devices must likewise be invented. Simultaneously, the need for grid storage is also being driven by the evolving nature of the grid (green grid, smart grid, and the distributed nature of the grid) as well as by other technological developments including vehicle electrification. Redox flow batteries, a rechargeable system that uses the redox states of various species for charge/discharge purposes, represent a highly promising approach, provided higher energy densities and lower-cost materials can be developed [1].

Work was therefore undertaken to advance state-of-the-art materials for flow battery energy storage. We have focused on non-aqueous systems because they potentially offer wider voltage windows, higher charge cycle efficiency, decreased temperature sensitivity, increased cycle life, and in some instances even favorable cost projections. Specifically, we have invented a method for synthesizing low-cost ionic liquids (ILs) with reducing-oxidizing (redox) transition metal species for incorporation into a flow cell configuration, relying on the difference in redox

potentials of two different ILs to establish the cell voltage. The ionically conductive ILs act as both electrolyte and active material, and, since they have no vapor pressure, ameliorate safety issues related to cell pressurization.

DESCRIPTION The transition-metal-based ionic liquid (MetIL)

electrolytes are prepared in a single step simply by heating metal salts with an appropriate combination of ligands (typically aminoalcohols). The synthesis is highly scalable and facilitates molecular-level engineering of many of the physicochemical properties of the MetILs. To date we have examined over 100 possible metal salt/ligand combinations, of which approximately 20 look promising.

Our focus has primarily been on large asymmetric cations to help lower the melting point. By modifying the symmetry of transition-metal-based coordination cations with polarizable amine and hydroxyl groups, we have created an electronically asymmetric secondary coordination sphere illustrated in Figure 1 that perturbs ion pairing. The partial positive and negative charges are sufficiently distributed to limit interaction with an anion while simultaneously keeping electrons sufficiently mobile to either add charge to or remove charge from the metal ion at the center of the complex.

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Fig. 1. Three-dimensional ball-and-stick notation of a representative MetIL cation illustrating the partial positive and negative charge distribution in the secondary coordination sphere.

PERFORMANCE DATA

Table 1 gives the complete molecular formulas for 10 representative MetILs. In 2010, we published a proof-of-concept paper focusing on one MetIL, FeNH(CH2CH2OH)26[CF3SO3]3 [2]. Cyclic voltammograms (at varying scan rates) for this compound are illustrated in Figure 2A. The high viscosity and low conductivity of this compound prevented the direct acquisition of electrochemical data. As a result, measurements were performed by dissolving the iron IL in another more conductive (and conventional) IL. The complex displays several quasi-reversible waves attributed to Fe(III)/Fe(II) reduction and re-oxidation.

Table 1. Molecular formulas of 10 representative MetILs. CeNH2CH2CH2OH8[CF3SO3]3 CuNH2CH2CH2OH6[CH3(CH2)3CH(C2H5)CO2]2 CuNH(CH2CH2OH)26[CH3(CH2)3CH(C2H5)CO2]2 CuNH(CH2CH2OH)26[CF3SO3]2 CuNH(CH2CH2OH)26[(CF3SO2)2N]2 CuNH(CH2CH2OH)26[BF4]2 Co NH2CH2CH2OH6[CF3SO3]2 FeNH(CH2CH2OH)26[CF3SO3]3 MnNH(CH2CH2OH)26[CF3SO3]2 NiNH2CH2CH2OH28[CF3SO3]3 ZnNH2CH2CH2OH6[CF3SO3]2

In contrast to the iron IL, a manganese compound, MnNH(CH2CH2OH)26[CF3SO3]2, was

prepared that displays fully reversible Mn(II)/Mn(III) oxidation and re-reduction (Figure 2B, at 50 mV/s scan rate and dissolved in the more conductive IL) [3]. This compound also displays improved conductivity over the iron IL, but the viscosity (~12000 cP) is not practical for a flow cell. Although both the manganese and iron ILs consist of dihydroxyamine ligands and triflate anions, infrared data indicate that the iron preferentially coordinates through the hydroxyl groups whereas manganese coordinates through the amine.

Fig. 2. Cyclic voltammograms of the iron (A) and manganese (B) ILs dissolved in a more conductive IL at various scan rates; the working electrode is glassy carbon and the counter electrode is platinum.

A number of copper ionic liquids have also been synthesized. The low symmetry of the tetragonally distorted d9 Cu(II) cation makes it particularly amenable to the modification of select physicochemical properties (including viscosity and conductivity). However, reduction of Cu(II) to Cu(I)

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results in an energy-consuming geometry change that makes it challenging to obtain reversible electrochemistry.

We have also recently prepared compounds containing either Co(II), Ni(II), Zn(II), or Ce(III). By far the most promising compound in terms of viscosity and conductivity was the cerium IL, CeNH2CH2CH2 OH8[CF3SO3]3. This is most likely attributed in part to the expanded coordination number of cerium (eight-coordinate) in contrast to the six-coordinate iron or manganese, for example. In addition, the Shannon-Prewitt ionic radius of eight-coordinate Ce(III) is 114 picometers, nearly double that of most first-row transition metals [4]. However, the high cost of cerium and the poor reversibility of the Ce(III)/Ce(IV) redox couple has prompted us to return focus to first-row metals with the caveat that emphasis be placed on expanded coordination and larger/bulkier ligands (including some aromatics) that can effectively increase the net radius of the coordination complex. The structure of one such representative compound is shown in Figure 3.

Fig. 3. Representative MetIL cation containing bulkier aromatic and hydroxamine ligands.

SUMMARY

A new family of redox-active ionic liquids for flow battery applications has been developed by Sandia National Laboratories. Most compounds are quite inexpensive to produce and some show promising viscosity, conductivity, or electrochemical reversibility. New compounds are continuing to be developed and tested, and cell test data are forthcoming.

REFERENCES [1] M. Skyllas-Kazacos, M.H. Chakrabarti, S.A. Hajimolana, F.S. Mjalli, and M. Saleem, “Progress in Flow Battery Research and Development,” J. Electrochem. Soc. 158, Issue 8, 2011, pp. R55-R7.

[2] T.M. Anderson, D. Ingersoll, A.J. Rose, C.L. Staiger, and J. C. Leonard, “Synthesis of an ionic liquid with an iron coordination cation,” Dalton Trans. 39, Issue 37, 2010, pp. 8609-8612.

[3] H.D. Pratt III, A.J. Rose, C.L. Staiger, D. Ingersoll, and T.M. Anderson, “Synthesis and characterization of ionic liquids containing copper, manganese, or zinc coordination cations,” Dalton Trans. 2011.

[4] R.D. Shannon, “Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides,” Acta Cryst. A32, 1976, pp. 751-767.

BIOGRAPHICAL NOTE Conference presenter: Travis M. Anderson (Ph.D., Emory University, 2002) is a staff member in Sandia National Laboratories’ Advanced Power Sources Research and Development group. His research

interests focus around the synthesis and characterization of redox-active coordination complexes, flow batteries, and thermal battery aging.

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Session 5 – Emerging Energy Storage Technology

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ZINC/AIR – A LOW-COST, LONG-LIFE AND, SAFE BATTERY TECHNOLOGY

Michael Oster

Eos Energy Storage, 3700 Glover Road, Easton, PA, USA

ABSTRACT Zinc (Zn)/Air batteries are inherently low-cost and energy-dense. The air electrode enables oxygen in ambient

air to be used as the oxidizing cathode reactant that does not need to be carried on board – saving materials cost and volume. Eos Energy Storage will present its research and developments in Zn/ir battery architecture, electrolyte, catalyst, and materials that the company believes resolves Zn/Air’s historic recharge limitation. With long life (potential up to 10,000 cycles/30 years at full depth of discharge) and with 6 hours storage, Eos believes that its Zn/Air technology could become one of the lowest-cost-per-kilowatt hour (kWh) battery technologies.

Our presentation will demonstrate the longest cycle life we believe has been achieved on a metal air battery to date (> 1,600 one-hour cycles thus far with no physical degradation) and the reasons why this technology could cost a fraction of the cost per kilowatt hour (kWh) of lithium (Li)-ion batteries, and also why it has the potential to become one of the safest and most energy-dense battery systems.

Technical issues addressed in our research include a system that does not utilize a membrane or separator and thus avoids what is an expensive and nondurable component. We have developed a neutral electrolyte that is not susceptible to dendrite formation and does not absorb CO2 or carbonates, thus preserving the life of the air electrode. Our electrolyte additives result in minimal corrosion of zinc (Zn). We have developed an electrolyte management system that avoids pressure and rupture when electrolyte density changes with state of charge. Our neutral electrolyte is nontoxic and nonflammable. Safety has been one of our key areas of focus.

We have utilized only non-noble materials as catalyst and electrodes. For our metal current collectors, we developed a proprietary treatment to coat the surface to a stable and conductive material to ensure that neither corrosion nor oxidation reduces electrode conductivity over time. Eos has also implemented an architecture that makes our Zn/Air system amenable for mass production with low capital investment by utilizing common manufacturing methods including printing of air

electrodes, injecting molding, and metal stamping of the remaining components.

With our materials, electrolyte, architecture, and manufacturing methods, and assuming reasonable performance assumptions, our detailed bill of materials shows a cost projection well below our projected market price of $160 per kWh even in the initial stages of production. Given the early stage of development of this technology, we believe that we could lower costs further and improve current density potentially by a large factor to bring costs to an even lower level. Our materials, architecture, and systems also give our Zn/Air system a potentially long life. Our electrolyte is safe, stable, and benign. We believe that this combination of innovations could lead to a battery system that could be transformative for utility and vehicle applications.

BIOGRAPHICAL NOTE Conference presenter: Michael Oster, CEO of Eos Energy Storage (formerly Grid Storage Technologies). Mr. Oster co-founded Eos in 2007 to develop and commercialize a utility-scale Zinc/Air battery system, which is a low-cost, energy-dense and safe battery technology with 6+ hours of storage. Mr. Oster previously was one of the larger developers of solar power assets in the northeastern United States together with a major European utility. Mr. Oster began his career in strategy and business planning for IBM and later joined the international management consulting firm of A. T. Kearney. In the last decade, Mr. Oster formed and capitalized an early-stage venture capital firm in New York City. He was one of

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the original partners to launch the global energy technology firm Oilspace/Aspect Enterprise, where he populated the board and investor group with OPEC oil ministers, U.S. cabinet members, and other energy industry leaders. Earlier, Mr. Oster moved to Russia as privatization started, built a real estate

investment and development company, and later established the first institutional real estate investment fund in Russia with the AT&T pension fund and Nomura Bank. Mr. Oster received his MBA in finance from New York University his B.A. in economics from Brandeis University.

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THE AQUEOUS ELECTROLYTE SODIUM ION BATTERY:

A LOW-COST SOLUTION FROM AQUION ENERGY

J. F. Whitacre,1,2 Sneha Shanbhag,2 David Blackwood,2 Eric Weber,2 Alex Mohamed,2 Wenzhou Yang,2 and Ted Wiley2

1Department of Materials Science and Engineering, Department of Engineering and Public Policy, Carnegie Mellon, University, Pittsburgh, PA, USA

2Aquion Energy, Pittsburgh, PA, USA

ABSTRACT

A new low-cost energy storage solution is presented that is based on an alkali-ion manganese-oxide intercalation cathode (positive electrode) and low-cost activated carbon anode (negative electrode). The electrolyte is a neutral pH solution containing dissolved sodium sulfate (Na2SO4) and the battery current collection and packaging system is comprised of low-cost materials produced and processed by highly scalable manufacturing techniques. Results presented include a description of the device and materials, an assessment of battery performance, and a description of ongoing large-scale demonstration projects.

Keywords: Sodium ion battery, hybrid supercapacitor, low-cost energy storage, flow battery, NaS battery, lead-acid battery

INTRODUCTION

As the electricity grids of the world grow and age, and as renewable power sources (such as solar arrays, wind turbines, micro sterling engines, solid oxide fuel cells) proliferate, there is an increasing need for large-scale secondary (rechargeable) energy storage capability. Both distributed and centralized systems are needed, with storage capabilities ranging from under 10 kilowatt hours (kWh) to hundreds of megawatt hours (MWh). Batteries for these stationary applications are typically based on the lead-acid, sodium sulfur (NaS), or lithium-ion (Li-ion) chemistries, and to date there are hundreds of MW of installed capacity for a total of thousands of MWh globally. Further, it is predicted that the annual global market for stationary storage will exceed $20B by 2021 [1].

While the current state-of-the-art electrochemical batteries are functional and appealing for some applications, there is still a need for a lower-cost, more stable, longer-lived chemistry. Proposed solutions include a range of flow batteries, low-cost Li-ion chemistries, advanced lead-acid, and next-generation NaS. Of these, it is not apparent which

will be able to be manufactured in a timely fashion at the right cost at the required scale. The approach described here represents a new alternative. By first assessing raw materials cost and availability of potential precursor materials, and then only accepting those that meet cost and performance criteria into the device development pipeline, we have arrived at a uniquely optimized device.

Work was therefore undertaken starting in 2008 to develop an aqueous electrolyte sodium ion battery system based on interaction electrodes. The resulting technology allows for the use of thick format electrodes (on the order of multiple millimeters), extremely inexpensive separator and current collector materials, and the use of benign electrolyte salts. The cells can be assembled in an open-air environment using simple equipment, and so can be manufactured at a very low cost.

DESCRIPTION Sodium is probably the most readily available

and inexpensive alkali metal and has very similar electrochemical characteristics as Li. Furthermore, Na actually demonstrates better ionic conductivity in

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aqueous solution. There are a handful of high-performing Na-based intercalation electrode materials systems that have been shown to function in non-aqueous environments, and of those, manganese (Mn)-based cathode materials systems were determined to be most cost-advantaged. There are many potential anode materials that might function; however, low-cost activated carbons offer particularly appealing robustness and performance attributes.

The core device, therefore, consists of an activated carbon anode with a proprietary surface preparation to significantly enhance specific pseudocapacitance, a λ-manganese dioxide (MnO2) alkali-ion intercalation cathode, and a non-woven fibrous separator. These active materials are mixed with a binder and are processed into multi-millimeter-thick freestanding electrodes. These electrodes and separators are then configured into large-format polypropylene battery packages using a true stacked prismatic architecture. The Aquion Battery 0 engineering/manufacturing model unit has an energy density of approximately 30 Wh with a usable voltage range of up to 0.5 to 1.8 volts.

PERFORMANCE DATA Figure 1 shows an image of the Aquion Battery 0

device and a typical 10-hour discharge curve indicating a total capacity of over 30 Wh. The internal volume of this device is approximately 1 liter, and the external volume is larger, but is not optimized to maximize energy density.

Fig. 1. Image of packaged battery (top) and 10-hour rate discharge curve (bottom).

Figure 2 indicates the energy density of the electrode pairs contained inside this battery unit.

Fig. 2. Energy density of the Aquion Energy electrode stack as a function of discharge time.

These data indicate that >80% of the total possible battery energy can be extracted at discharge times exceeding 4 hours.

The data plotted in Figure 3 show the cycle life performance of the battery under deep discharge galvanostatic use conditions.

Fig. 3. (a) Battery current and voltage profiles as function of time for deep-discharge constant-current cycle life testing. (b) Cycle life results for 15 months of deep-discharge testing for a representative test fixture. These data indicate the long-term stability of the battery chemistry.

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High-temperature testing indicates that this chemistry is also very stable to temperatures at least as high as 60 ˚C. Application-specific-use profile testing also shows that this solution is excellent for a range of stationary storage uses.

SUMMARY A new hybrid/asymmetric battery chemistry has

been developed and scaled to pilot manufacturing level by Aquion Energy. This very low-cost battery chemistry exhibits excellent stability over long-duration use and acceptable energy density values. Large-scale demonstrations of this technology are currently under development and test, and data from these tests are forthcoming.

REFERENCES [1] Pike Research Report, “Energy Storage on the Grid,” 2011, at www.pikeresearch.com/research/ energy-storage-on-the-grid

BIOGRAPHICAL NOTE

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Conference presenter: Dr. J.F. Whitacre received a Ph.D. from the University of Michigan in 1999. He held various positions at Caltech and the Jet Propulsion Laboratory before taking his current Professorship at Carnegie Mellon University (CMU) in 2007. There he develops

functional materials systems and performs economic/environmental impact assessment for energy technologies. His early work at CMU resulted in the conception of a novel scalable energy storage device. In 2008 he founded Aquion Energy, a company that has grown to over 60 employees. He is currently on leave from CMU to serve as full-time Chief Technology Officer for Aquion as it scales a pilot manufacturing plant in Pittsburgh, Pennsylvania. Professor Whitacre has over 50 peer-reviewed papers and patents.

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THERMAL ENERGY STORAGE AS AN ENABLING TECHNOLOGY FOR RENEWABLE ENERGY

Paul Denholm

National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO, USA

The ultimate limit to supplying a large fraction of the nation’s electricity demand from variable generation sources such as wind and solar is the supply/demand characteristics of the renewable resource. In many parts of the United States there is limited correlation between the solar resource and demand, while the wind resource is often anti-correlated with demand. At low penetration, wind and solar generation can be accommodated and make a valuable contribution to the electricity supply during all periods. However, at higher penetration, variable generation may need to be curtailed due to lack of demand during some hours, while meeting only a small fraction of demand during others.

Energy storage is commonly seen as an important enabling technology for large-scale deployment of variable renewable energy sources such as wind and solar. However, many energy storage technology assessments ignore the potential use of thermal energy storage (TES) as a method of increasing the penetration of solar and other renewables.

There are two forms of thermal storage we examine in this work. The first is the use of TES with concentrating solar power (CSP). CSP/TES is a highly dispatchable source of energy, with high ramp rates and range. This feature allows it to increase the flexibility of power systems, enabling greater use of other variable generation sources such as photovoltaics (PV) and wind.

The second technology examined is TES for space cooling. Space cooling is a significant use of energy in the United States, representing about 10% of total demand. Cooling also drives the peak electricity demand and the need for peaking generation capacity. Potentially a large fraction of this cooling electricity demand could be shifted via cold storage in ice or chilled water. End-use thermal storage could be dispatched to maximize the use of renewable sources and also to provide ancillary services.

Both forms of TES add several advantages over conventional electricity storage technologies. Storing thermal energy is often more efficient than storing electrical energy. In CSP plants, TES can achieve efficiencies well over 90%. End-use thermal storage can also achieve very high efficiencies and has the ability to be sited at the load, avoiding losses in the transmission and distribution network. The primary disadvantage of TES is that it is tied to a single application, and cannot be used to store grid electricity. (While theoretically it could be used for grid storage, the round-trip efficiency of this use would be well under 50%.) CSP can only be deployed in locations with significant direct solar radiation, restricting its application in the United States largely to the desert southwest. Cold storage is economically restricted to locations with significant cooling demand. As a result, there are significant geographical restrictions on the use of TES as a renewable enabling technology.

This study examines the system flexibility that can be realized by deploying concentrating solar power with TES, focusing on the southwestern United States. Simulations of large-scale deployment of combinations of CSP/TES, PV, and wind were performed, examining the feasible contributions of renewable sources, considering the limits of thermal generation and system flexibility.

Figure 1 illustrates several of the challenges of deploying large amounts of wind and solar without enabling technologies such as thermal storage. The figure is a dispatch stack in the western United States, considering a future scenario where PV provides 15% of the annual energy demand and wind provides an additional 15%. The period is May 1 through 4 based on weather conditions in 2005. During each day the large amount of mid-day PV generation forces conventional units to cycle over a large range. Even nuclear plants are forced to reduce output to accommodate PV production. Given the limited ability to ramp large thermal units, this would likely result in curtailed PV generation to avoid excessive cycling of coal and nuclear plants.

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Fig. 1. Dispatch of the western U.S. grid where renewables provide 30% of annual demand.

Figure 2 illustrates how replacing some PV

generation with dispatchable CSP could be used to shift solar generation and reduce ramping requirements. Solar still provides 15% of the total energy demand, but requires far less ramping of large thermal units.

Fig. 2. Dispatch of the western U.S. grid where renewables provide 30% of annual demand, but including CSP/TES.

An important component of adding CSP/TES is

the rapid ramping capability, firm capacity, and the ability to provide operating reserves. This means that CSP/TES can be complementary to wind and solar, and actually enable greater use of these variable resources. Since it provides firm capacity, CSP/TES can replace conventional thermal generators that may have less ramping rate and range. Figure 3 illustrates the ramping requirement in a high renewable scenario. If not dispatched, the production of CSP and PV would obviously coincide during the middle of the day. This would produce excess solar generation. This can be observed by comparing the output of a CSP plant if it did not have storage (blue

line) with the CSP/TES generation as dispatched (red line). Furthermore, the rapid ramping requirements, minimum generation constraints, and reserves requirements may require some of the solar generation to be curtailed. However, adding TES to CSP allows nearly all the CSP generation to be shifted and provide rapid ramping to follow the significant increase in net load variability introduced by solar and wind. This can potentially reduce renewable curtailment. By providing these services with fast-response CSP, TES can reduce the integration challenge introduced by variable wind and solar PV.

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Similarly, cold storage can potentially provide

similar benefits to wind and solar. Figure 4 illustrates the limited coincidence of wind and solar patterns during four summer days in the western United States. Demand due to cooling loads peaks at about 4 to 6 p.m., while solar peaks at about 1 p.m. This results in limited capacity benefits of solar and wind, and the need for large amounts of conventional generation. Cold storage can potentially add loads during periods of high wind and solar output, reducing cycling impacts on conventional generators, and reducing the need for peaking capacity.

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BIOGRAPHICAL NOTE Conference presenter: Paul Denholm is a Senior Energy Analyst in the Strategic Energy Analysis Center at the National Renewable Energy Laboratory. His research interests include examining the technical, economic, and environmental benefits and impacts of large-scale deployment of renewable electricity generation, including the role of enabling technologies such as energy storage, plug-in hybrid

electric vehicles, and long-distance transmission. His analysis focuses on modeling electric power systems using grid simulation tools with an emphasis on bulk storage technologies, including compressed air, pumped hydro, long-duration batteries and thermal storage. He holds a B.S. in physics from James Madison University, an M.S. in instrumentation physics from the University of Utah, and a Ph.D. in environmental studies and energy analysis from the University of Wisconsin–Madison.

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ADVANCED ELECTROCHEMICAL STORAGE RD&D AT PACIFIC NORTHWEST NATIONAL LABORATORY FOR RENEWABLE

INTEGRATION AND GRID APPLICATIONS

Z. Gary Yang, Daiwon Choi, Greg Coffey, Jianzhi Hu, Cui Jun, Jin Yong Kim, Soowhan Kim, Michael, Kintner-Meyer, Dean Mattson, Kerry Meinhardt,

Vijay Murugesan, Zimin Nie, John Lemmon, Guosheng Li, Liyu Li, Jun Liu, Xiaochun Lu, David Reed, Yuyan Shao, Vince Sprenkle, Vish Viswanathan,

Wei Wang, Bao Wei, Xu Wu, and Gordon Xia

Pacific Northwest National Laboratory, Richland, WA, USA

ABSTRACT

Pacific Northwest National Laboratory (PNNL) has conducted extensive research and development in the past few years in electrical energy storage for renewable integration and grid applications. The efforts have been supported by the Department of Energy Office of Electricity and Energy Reliability (DOE-OE), Advanced Research Projects Agency–Energy (ARPA-E), and internal funding, with focus on electrochemical storage technologies or batteries that include redox flow, sodium (Na)-metal halide and unique lithium (Li)-ion batteries, as well as some new concepts. To transform science to technologies, PNNL is closely working with industries in developing advanced components, cells, and prototypes. Our grid analytics help define the needs with the U.S. grid, which also guides the storage technology research, development, and demonstration (RD&D). This paper offers an overview and update on the progress of our efforts in various battery RD&D for the stationary applications.

Keywords: redox flow battery, Na-metal halide battery, Li-ion battery, Na-ion battery, renewable integration

Electrical energy storage (EES) is a vital enabler

for transforming the electrical grid into the 21st century. Energy storage provides grid stability to integrate intermittent renewable energy resources into the grid as well as improving the overall utilization of the entire electricity infrastructure. There are various potential storage technologies for the stationary applications. However, the current technologies are either constrained by specific site selection (pumped hydro or compressed air storage) and/or cannot meet the performance and cost requirements for broad market penetration. To address the cost and performance challenges for advanced energy storage systems, Pacific Northwest National Laboratory (PNNL) has utilized electrochemical devices and advanced materials development capabilities to advance the stationary electrical storage technologies or batteries with near-term and longer-term goals. Also, an integral part of our efforts is on grid system analytics that further define the needs of the storage with U.S. grids and help guide the battery research, development, and demonstration (RD&D).

The battery RD&D portfolio at PNNL, as shown in Figure 1, includes existing technologies that have evolved over the past few decades, but had issues to meet the performance and cost requirement matrices for broad market penetration [1]. Particularly we have

Fig. 1. PNNL portfolio of electrical grid energy storage research, development, and demonstration.

Risk

High Risk,High Payoff

Low Risk,Evolutionary

BasicScience

Research

FeasibilityResearch

TechnologyDevelopment

TechnologyDemonstration

Small Scale Deployment

Large Scale Deployment

Technology Readiness Level

o New gen redox flow batteryo Planar Na-metal halide battery

o Unique Li-ion battery

Existing technologies

o Na+ intercalation materials and Na-ion battery

o Hydride-air battery

Emerging technologies

Demonstration, grid integration

PNNL portfolio in stationary storage RD&D

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focused on three technology areas: aqueous based redox flow, sodium (Na)-metal halide, and unique lithium (Li)-ion batteries. In addition to accelerating commercialization of the existing technologies, PNNL has actively developed new EES concepts that can lead to transformational advances in performance and cost reduction. For example, in this past year, a Na-ion battery has been proved at room temperature, following discovery of Na-ion intercalation compounds.

NOVEL REDOX FLOW BATTERIES With a redox flow battery (RFB) PNNL has

aimed to develop low-cost, high-performance RFBs through collaboration with U.S. leading industries and universities (see Figure 2). In this past year, PNNL has made breakthroughs in the development of key component materials and chemistries for RFBs. New redox couples and supporting electrolytes based on halide and sulfate mixed chemistries have been discovered with significant advantages in stability, energy density, and cost, over the current all-vanadium sulfate systems. The mixed chloride and sulfate chemistries demonstrated a much improved stability, allowing for 75% increase in energy density and significant extension in operating temperatures (-5~55 oC) over the current technologies (10~35 oC), while being still highly reversible and efficient [2]. Alternatively, pairing of vanadium with iron, a more cost-effective replacement of vanadium, resulted in a substantially improved compatibility, allowing use of more cost-effective separators in the place of Nafion-membranes and avoiding gas release [3]. The ease in operation requirements, use of low-cost alternative components, and improved performance parameters all help reduce capital and life-cycle costs. In addition to electrolytes, PNNL has worked with DuPont, Daramic LLC, Fumatech, SGL, Graphtec, and others to screen and select the best membranes/separators and graphite felt electrodes. We have worked with Penn State University through subcontract to develop low-cost hydro-carbon alternatives to the Nafion membranes for RFB applications. Currently, bench-top systems are being assembled to further validate the new electrolytes and other components. Prototypes will be developed with collaboration with industries.

Fig. 2. Research and development of next-generation redox flow batteries at PNNL.

PLANAR NA-METAL HALIDE BATTERIES

The Na-metal halide battery was built in tubular designs and operated 300~350 oC since its invention a few decades ago. PNNL, teaming up EaglePicher Technologies LLC, is developing and demonstrating planar Na-metal halide batteries that can operate at lower temperatures with improved performance and allow use of more cost-effective stack materials. The team has successfully proved the concept of the planar design [4]. Interfaces and electrode chemistries have been optimized for the new designs (see Figure 3). Currently we are scaling up and assembling stacks to eventually deliver a 5-kW prototype. Meanwhile, efforts have been initiated to develop and optimize new cathodes, electrolytes, and interfaces to further reduce the operating temperatures.

Fig. 3. Research and development of planar Na-metal halide batteries at PNNL.

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UNIQUE LI-ION BATTERIES PNNL has searched unique chemistries for Li-ion

batteries that can demonstrate a longer cycle life and lower cost that the conventional ones currently of interest for vehicle applications. Our focus has been on developing low-cost electrode materials and demonstrating cells that are made from the cost-effective electrodes. Particularly, we have developed and optimized titanium dioxide (TiO2) base anode and LiFePO4 base cathode Li-ion batteries, intended for community storage. Nanocomposite electrode structures were developed to overcome the low electron conductivity issue of the materials. Over 1,000 deep cycles have been demonstrated for the Li-ion cells with only negligible capacity loss [5]. Currently we are developing new cathodes made from Li(Mn,Fe)PO4 materials and evaluating the cells made from the cathodes.

EMERGING TECHNOLOGIES Our efforts in emerging technologies have

focused on proving new battery concepts that can lead to significant reduction in costs and performance. In this past year, we have developed single crystalline Na4Mn9O18 nanowires as the positive electrode that allowed facile Na+ intercalation and deintercalation. The Na-ion batteries (half-cells) made from the nanostructured material demonstrated a high reversible capacity and exceptional cycling performance. The Na4Mn9O18 nanowire electrode material, after calcination at 750 oC, delivered a reversible capacity of 128 mAh g-1 at 0.1 C (1 C corresponds with 120 mA g-1) with an excellent initial capacity retention capability of 77% even after 1000 cycles at 0.5 C (see Figure 4) [6]. Our current efforts are to search for new carbon-based negative electrodes so a full cell with commercial organic liquid electrolyte can be demonstrated in the future.

Fig. 4. Schematic and performance of a Na-ion battery made from a Na4Mn9O18 nanowire electrode.

REFERENCES [1] Yang et al., “Electrochemical Energy Storage for The Green Grid,” Chem. Reviews 111, 2011, p. 3577.

[2] Li et al., “A Stable Vanadium Redox-Flow Battery with High Energy,” Adv. Energy Mat. 1, 2011, p. 394.

[3] Wang et al., “A New Redox Flow Battery Using Fe/V Redox Couples in Chloride Supporting Electrolyte,” Energy & Environ. Sci., available online.

[4] Lu et al., “High Power Planar Sodium-Nickel Chloride Battery," ECS Transact, 28, 2011, p. 7.

[5] Choi et al., “Li-ion Batteries from LiFePO4 Cathode and Anatase/Graphene Composite Anode for Stationary Energy Storage,” Electrochem. Comm. 12, 2010, p. 378.

[6] Cao et al., “Reversible Sodium Ion Insertion in Single Crystalline Manganese Oxide Nanowires with Exceptional Long Cycle Life,” Adv. Mat.,23, 2011, p. 3155.

BIOGRAPHICAL NOTE Conference presenter: Dr. Zhenguo (Gary) Yang is a Lab Fellow at Pacific Northwest National Laboratory (PNNL) of the U.S. Department of Energy, where he conducts applied research into advanced materials and energy conversion and storage. Currently, he is

leading efforts in developing varied electrochemical energy storage technologies, in particular for renewable integration and grid applications. Previously he was a Chief Scientist and served as a technical lead in areas including solid oxide fuel cells, mixed conductive coatings, and hydrogen storage in nanostructured materials. Dr. Yang has authored/co-authored over 180 research papers and is an inventor/co-inventor of 16 U.S. patents. He is a fellow of ASM International. Dr. Yang received his Ph.D. in materials science and engineering from the University of Connecticut and worked as a postdoctoral fellow at Carnegie Mellon University before joining PNNL.

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Session 6 – Power Electronics

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BATTERY MODULE BALANCING WITH A CASCADED H-BRIDGE MULTILEVEL INVERTER

Matthew Senesky,1 Hao Qian,1 Kosha Mahmodieh,1 Shahrdad Tabib,1 and Chet Sandberg2

1National Semiconductor, Santa Clara, CA, USA 2Altair Nanotechnologies, Reno, NV, USA

ABSTRACT Electrochemical advances in lithium-ion batteries are now being complemented by advances in battery

management systems (BMSs). The larger-format lithium-ion storage systems can require significant control of module balance levels, as well as temperatures and other safety parameters. Most BMSs use passive balancing, where modest amounts of energy are allowed to bleed from stronger cells to adjust average per-cell charge over a long time period. The balancing of such systems is slow and reduces battery system efficiency. In addition, virtually all BMS solutions suffer from a high degree of vulnerability to a single component fault. This paper describes an active battery module balancing system based on a cascaded H-bridge multilevel inverter that improves the speed and efficiency of balancing, while providing fault tolerance in some situations.

Keywords: battery management system, multilevel inverter, lithium titanate

INTRODUCTION

Grid Storage

As significant penetration of renewable energy sources becomes a reality, and increasing load from plug-in electric vehicles appears on the horizon, renewed attention has been directed to well-known grid challenges ranging from frequency regulation at the Independent System Operator (ISO) level down to time-of-use charge management for individual residences. It is evident that energy storage will play a critical role in addressing these challenges. Recent publications [1,2] have quantified the economic benefits of various storage applications, as well as the costs associated with storage technologies. Battery-based storage is a viable contender for a subset of these applications. The following work presents a battery storage system appropriate for the modest energy and power demands of residential, commercial, and community storage systems.

Battery Management

Large battery systems present challenges in performance, safety, and reliability. Cell chemistry and manufacturing place an upper bound on these metrics. However, the operational features of a battery management system (BMS) to a large extent determine whether the overall system meets its anticipated goals in practice. A BMS typically consists

of cell voltage and temperature monitoring to prevent failures, and balancing circuits that compensate for capacity mismatch among cells and modules configured in series.

Modular Systems

Systems with more than about 10 cells are often subdivided into modules. This approach has advantages for both manufacturing and system design. A battery module typically has a cell-level BMS to address monitoring and balancing of cells within the module. However, module-to-module balance still must be managed.

MULTILEVEL INVERTERS Multilevel inverter topologies were first

described 20 to 25 years ago for high-voltage grid interface and motor drive applications [3-5]. The three basic topologies all share the useful features of having reduced semiconductor voltage ratings, and AC waveforms with low total harmonic distortion (THD).

Of the various multilevel topologies, the cascaded H-bridge inverter shown in Figure 1 is perhaps best suited to battery-based applications. The inverter can accommodate multiple DC sources, and has a highly modular structure. Using this configuration, a different level of power can be drawn

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from each DC source independently. In this manner, battery modules can be balanced while charging or discharging.

Fig. 1. A seven-level cascaded H-bridge inverter.

SYSTEM DESIGN

Battery Pack

An energy storage system has been designed in which three Altairnano [6] 23-volt (V) 50-Ah 1-p10s modules of lithium titanate (LiTO) chemistry are used. The Altairnano batteries are distinguished from other lithium chemistries by having nano LiTO spinel making up the anode instead of the conventional carbon. Their safety, very long life (16,000 cycles – full depth of discharge), high efficiency (>94% round trip 20 ºC), very wide operating temperature range (-40 ºC to +55 ºC) and quick charge capability (6 C rate – 10 minutes) make these batteries ideal for a number of applications, including renewable energy, transportation vehicles, and grid storage systems.

Power Semiconductors

The power switches in the multilevel inverter need to carry current in both directions to realize bidirectional power flow. A typical implementation uses Metal-Oxide-Semiconductor-Field-Effect-Transistors (MOSFETs) or Insulated-Gate Bipolar-Transistors (IGBTs) with anti-parallel diodes. Power MOSFETs can operate at a higher switching frequency than the IGBTs, resulting in a smaller filter size. In addition, new power MOSFETs are designed with exceptionally low on-state drain-to-source resistance (RDSon), resulting in reduced conduction loss. Therefore, the power MOSFETs were used in the inverter described here.

System Communication and Control

The control system consists of a master controller and a slave controller for each battery module. The master controller implements closed-loop control of the AC current to produce the desired power at unity power factor. If balancing of the modules’ voltages or state of charge (SoC) is desired, the duty cycle to each module can be adjusted based on measurements from the slave controllers. Note that since the modules are cascaded, the communication channel to each module must be galvanically isolated from the others.

EXPERIMENTAL RESULTS Operation

The prototype modular energy storage system is connected to a single-phase 120-V, 60-Hertz line through a 1:4 transformer to achieve proper voltage. The system can charge from or discharge to the line with power up to 3 kilowatts. Figure 2 shows typical waveforms measured at the inverter terminals: the characteristic stepped voltage waveform and a clean sinusoidal current waveform.

Fig. 2. Inverter voltage (stepped) and current (sinusoidal). Balancing

Because the inverter stages are connected in series and hence have the same current, the AC voltage of each stage determines the power drawn (neglecting losses) from the corresponding battery module. Thus module balancing is accomplished by a feedback loop from module voltage to inverter duty cycle. If an accurate SoC estimate is available, this can be substituted for module voltage.

The result of an experiment applying balancing control to three modules with mismatched SoC is shown in Figure 3. The initial mismatch of 422 millivolts (mV) corresponds to a 10% SoC mismatch. After one charge-discharge cycle at a 0.5 C rate, mismatch is reduced to 45 mV.

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Fig. 3. Battery module voltage balancing.

Efficiency

Figure 4 shows the experimental efficiencies of the multilevel inverter when power is transferred from the battery to the grid. The upper curve shows the efficiency without the AC filter, which peaks at 99.2% at 200 watts (W) output power. The bottom curve shows the efficiency with the AC filter, which is about 94% at 950 W output power.

Fig. 4. Measured inverter efficiency.

REFERENCES

[1] D. Rastler, Electricity Energy Storage Technology Options, Electric Power Research Institute, December 2010.

[2] J. Eyer and G. Corey, Energy Storage for the Electricity Grid: Benefits and Market Potential Assessment Guide, Sandia National Laboratories, February 2010.

[3] T.A. Meynard and H. Foch, “Multi-level conversion: high voltage choppers and voltage-source inverters,” IEEE PESC, 1992, pp. 397-403.

[4] F.Z. Peng et al., A multilevel voltage-source inverter with separate DC sources for static VAr generation,” IEEE IAS, 1995, pp. 2541-2548.

[5] J. Rodriguez et al., Multilevel Converters: An Enabling Technology for High-Power Applications, Proc. of the IEEE, November 2009, pp. 1786-1817.

[6] Altairnano Applications Kit, http://www.altairnano.com/.

BIOGRAPHICAL NOTES Conference presenter: Matthew Senesky received A.B. and B.E. degrees from Dartmouth College, and M.S. and Ph.D. degrees in electrical engineering from the University of California at Berkeley. His academic research

included topics in flywheel energy storage and micro-scale power generation. Since graduating in 2005, he has held positions at Artificial Muscle and Tesla Motors. In his current position at National Semiconductor, he performs research and development in power electronics for renewable energy, energy storage, and electric vehicle applications.

Chet Sandberg received a B.S. degree from the Massachusetts Institute of Technology and an MS from Stanford. He then joined the Chemelex Division of Raychem Corporation, where he managed technology projects for 30 years. In October 2002, he retired from Raychem/Tyco. He currently

consults for Altairnano, a lithium-ion battery manufacturer. He also consults with Athabasca Oil Sands Corporation, Trendpoint, and Energy Recovery Inc. on various electrical and mechanical engineering projects. He is also involved with Silicon Valley startups and is an angel investor in some. He is a member of the National Electrical Code Panel 17. In December 1999, Mr. Sandberg was honored by the Institute of Electrical and Electronics (IEEE) by being elevated to their highest member level of IEEE Fellow. He is also a Senior Member of the International Society of Automation (ISA), a member of the American Society of Mechanical Engineers (ASME), the National Fire Protection Association (NFPA), and the Society of Petroleum Engineers (SPE).

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Kosha Mahmodieh graduated with a B.Sc. from the Electrical Engineering and Computer Science (EECS) Department of University of California, Berkeley, with an emphasis on Digital and Analog Design in 2008. He joined National Semiconductor in 2007 and has been working on various “power”-related projects, such as photovoltaic and grid storage. He is currently studying part-time towards an M.S. in Analog/System Design.

Hao Qian received the B.S. and M.S. degrees in electrical engineering from Zhejiang University, China, in 2003 and 2006, respectively. He is currently working toward the Ph.D. degree at Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg. Since 2006, he has been a

Research Assistant at the Future Energy Electronics Center (FEEC), Virginia Tech. His current research interests include soft-switching converters, grid-tie inverters, and high-efficiency power conditioning systems for renewable energy and energy storage applications.

Dr. Shahrdad Tabib holds BEE and BME degrees from the University of Minnesota, Minneapolis, MSME from the University of California, Berkeley, and Ph.D. in Mechanical and Aeronautical Engineering from the University of California, Davis. He has been with National Semiconductor Corporation since 2009 working in the area of green and renewable energy systems.

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A POWER ELECTRONIC CONDITIONER USING ELECTROCHEMICAL

CAPACITORS TO IMPROVE WIND TURBINE POWER QUALITY

Murali Bottu,1 Mariesa Crow,1 and Stan Atcitty2

1Missouri University of Science and Technology, Rolla, MO, USA 2Sandia National Laboratories, Albuquerque, NM, USA

ABSTRACT

The large variability in wind output power can adversely impact local loads that are sensitive to poor power quality. To mitigate large swings in power, the wind turbine output power can be conditioned by using a small energy buffer. A power conditioner is developed to smooth the wind power output by utilizing the energy of an electrochemical capacitor, or ultracapacitor. The conditioner is based on a single-phase voltage source inverter connected between the grid interconnection point and the ultracapacitor. The voltage source inverter (VSI) shunt inverter injects or absorbs active power from the line to smooth the wind power output by utilizing the short-term storage capabilities of the ultracapacitor. The ultracapacitor is connected to the DC link through a bidirectional DC-DC converter. The bidirectional DC-DC converter and VSI are constructed and field-tested on a Skystream 3.7 wind turbine installed at the Missouri University of Science and Technology.

Keywords: power electronics, electrochemical capacitors, wind power

INTRODUCTION

Due to the price volatility and carbon impact of fossil fuels, wind power generation is rapidly growing as an alternative energy source in many parts of the world. Due to the intermittency of wind speed, wind turbine output power can be highly variable. Power fluctuations from the wind turbine may cause severe power quality problems when connected to the grid. The large variability in wind turbine output power can adversely impact local loads that are sensitive to pulsating power, posing a challenge to the use of wind power extensively. The rapid growth of the wind power and its immense potential as a future energy source encourage us to find a way to smooth the intermittent wind power. Energy storage technologies can be used to improve the quality of the wind power [1-2]. In this paper, we propose the power quality conditioner with the ultracapacitor to smooth the variable wind turbine output power. The short-term storage capabilities of the ultracapacitor can be effectively used to smooth the wind power to minimize rapid power excursions that may damage sensitive local loads.

This paper presents a power conditioner that has the purpose of smoothing the wind power. The power

conditioner mainly consists of power converters to shape the injected current at the point of common coupling [3]. The conditioner is based on a single-phase shunt voltage shunt inverter (VSI) connected between the grid interconnection point and the ultracapacitor. The shunt VSI injects or absorbs active power from the line to smooth the intermittent wind power by charging or discharging the ultracapacitor [4]. The ultracapacitor is connected to the DC link through a DC-DC converter. Traditionally, the VSI DC link voltage is maintained relatively constant by the shunt inverter control. In this application, we use a bidirectional DC-DC converter to maintain the DC link voltage. The bidirectional DC-DC converter acts in buck mode during discharge of the DC link and in boost mode during charging to maintain the voltage of the DC link to provide good controllability of the VSI.

Control of the injected active power via the shunt inverter is presented in this paper. The VSI controller calculates the compensating active power, which is then synthesized by using the bipolar pulse width modulation (PWM) switching sequence. The reference signal to the shunt inverter controller is obtained from a low pass filter, which has a large time constant. The fluctuating wind power is passed through the low pass filter to get the smoothed

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reference value. The conditioner ensures the smooth power is available at the grid interconnection point. The simulation results are presented to show the efficiency of the conditioner in smoothing the variable wind turbine output power.

The power conditioner design and control will be validated on the Skystream 3.7 wind turbine installed at the Missouri University of Science and Technology. The installed wind turbine is shown in Figure 1.

Fig. 1. Skystream wind turbine installed at the Missouri University of Science and Technology.

POWER QUALITY CONDITIONER

As shown in Figure 2, the power quality conditioner consists of a shunt inverter and a bidirectional DC-DC converter. The voltage source inverter acts as a shunt active filter compensating the active power of the wind turbine. The VSI is connected to the line through an resistor-inductor (RL) filter that reduces the unwanted harmonics. The shape of the output current of the conditioner depends on the inductor value. The value of the resistor and the inductor determines the damping in the circuit. On the other side, the VSI is connected to the DC link capacitor. The DC-DC converter with the ultracapacitor is used to reduce the size of the DC link capacitor and to maintain the voltage of the DC link relatively constant as the ultracapacitor discharges and charges. The bidirectional DC-DC converter charges the ultracapacitor in buck mode by reducing the voltage of the DC link. In the other direction, it acts in boost mode, discharging the ultracapacitor to increase the voltage of the DC link. The power conditioner injects or absorbs active power from the line through the filter to smooth the variable wind turbine output power. The DC link acts as the voltage source for the VSI.

DC-DC converterUcap DC

Link

Shunt Inverter

+

-

DC-DC Converter Controller

PWM Shunt Inverter

Controller

AC Load

PCCis

i inv

iL

Lsh Rsh

PsPrefVref Vdc

S1 S2 g1 g2 g3 g4

Fig. 2. Power quality conditioner.

The primary objective of the conditioner is to

inject a current iinv(t) at the load such that the load current is relatively smooth. The smoothed current is obtained by passing the (measured and scaled) wind turbine current through a low pass filter that is tuned to provide the appropriate high-frequency cutoff. The electro-chemical capacitor is charged and discharged rapidly to supply the required current. Note that the reference (load) current is not constant, but rather a slowly varying current. If the reference current were held constant, this would imply that the electrochemical capacitor would have infinite ability to charge and discharge. By allowing the reference current to slowly vary, the energy to the load will not exceed the energy of the wind turbine (less losses). The conditioner is shown in Figures 3 and 4.

Fig. 3. Conditioner interconnections.

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Fig. 4. Power quality conditioner hardware.

The measured injected current of the conditioner

is shown in Figure 5. The blue trace is the measured unconditioned (raw) output of the wind turbine. It is highly variable with large pulsations in power and with considerable high-frequency noise. The red trace is the actual measured conditioned output current of the conditioner with a 60-second filter time constant. The green trace is a simulated conditioned output current if a 5-minute filter time constant were used.

0 100 200 300 400 500 600 700 800 900 10005.4

5.5

5.6

5.7

5.8

5.9

6

6.1

time (seconds)

inje

cted

cur

rent

(A)

unconditioned currentconditioned currentsimulated current

Fig. 5. Power quality conditioner output currents.

REFERENCES [1] P.F. Ribeiro, B.K. Johnson, M.L. Crow, A. Arsoy, and Y. Liu, “Energy Storage Systems for Advanced Power Applications,” Proceedings of the IEEE 89, no. 12, 2001, pp. 1744-1756.

[2] Ming-Shun Lu et al., “Combining the Wind Power Generation System With Energy Storage Equipment,” IEEE Trans. Industry Appl, 45, no. 6, 2009.

[3] Chih-Chiang Hua and Chia-Cheng Tu, “Design and implementation of power converters for wind generator,” in IEEE Industrial Electronics and Applications Conf., 2009, pp. 3372-3377.

[4] M.S.A. Dahidah, N. Mariun, S. Mahmod, and N. Khan, “Single phase active power filter for harmonic mitigation in distribution power lines,” in Proc. 2003 IEEE Power Engineering Conf., pp. 359-362.

BIOGRAPHICAL NOTE

Conference presenter: Mariesa L. Crow is the F. Finley Distinguished Professor of Electrical Engineering at the Missouri University of Science and Technology (Missouri S&T). She received her B.S. in Electrical Engineering from the University of

Michigan and her Ph.D. in Electrical Engineering from the University of Illinois – Urbana/Champaign. Her area of professional interest is computational methods and power electronics applications to renewable energy systems. She is currently the Director of the Energy Research and Development Center at Missouri S&T. She is a Registered Professional Engineer in the State of Missouri and a Fellow of the Institute of Electrical and Electronics Engineers.

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DEGRADATION MECHANISMS AND CHARACTERIZATION TECHNIQUES

IN SILICON CARBIDE MOSFETs AT HIGH-TEMPERATURE OPERATION

R.J. Kaplar, S. DasGupta, M.J. Marinella, B. Sheffield, R. Brock, M.A. Smith, and S. Atcitty

Sandia National Laboratories, Albuquerque, NM, USA

Due to a number of advantages over silicon,

including higher breakdown field, higher operational junction temperature, and higher thermal conductivity, silicon carbide (SiC) has generated keen interest as a material of choice for power electronic devices. Device characteristics resulting directly from SiC’s superior material properties, including enhanced ability to withstand high voltage, lower on-state resistance and capacitance permitting higher switching frequency, and reduced thermal management requirements, give SiC-based power devices the potential to greatly reduce the system footprint and cost, and to increase system efficiency. Among all the possible semiconductor switches, the field-effect transistor provides very low switching loss and is thus an attractive option, especially at high switching frequency. A SiC metal-oxide semiconductor field-effect transistor (MOSFET) is now commercially available that provides a blocking voltage of 1200 volts (V), maximum DC current capability of 33 amps (A), and on-state resistance Ron of 80 milliohms (mΩ). However, the reliability of the silicon oxide (SiO2) insulator on SiC at high temperature is an open question. The predominant degradation trends in this MOSFET under high-temperature overvoltage and pulsed overcurrent stress are reported in this work. We also describe the development of a microcontroller-based condition monitoring module that can track changes in the semiconductor device characteristics in order to improve real-world system availability.

SiC MOSFETs have traditionally suffered from poor oxide-semiconductor interface quality, which has led to large threshold voltage instability [1]. Fortunately, recent process improvements have mitigated this problem to a large degree. In particular, the commercially available MOSFET (or in some cases, pre-production versions of the same MOSFET) that we studied showed no signs of degradation when operated below the maximum temperature specified

by the manufacturer (125 °C). However, significant degradation is evident if the temperature of the device is raised above 125 °C (Figure 1).

Fig. 1. Id-Vg characteristics of SiC MOSFET stressed at various temperatures (Vg = +20 V, Vd = 0.1 V).

On the drain current versus gate voltage (Id-Vg)

curves shown, a shift in the subthreshold portion of the curve is evident after stress at 175 °C, and is much more severe after stress at 225 °C. Analysis of these curves indicates a large (on the order of 1012 cm-2eV-1) density of electrically active traps at the SiC/SiO2 interface, as well as the presence of charge trapped in the SiO2 gate [2], consistent with electron trapping. Bias under negative gate polarity (which does not turn the device on, but the device could still see negative gate pulses during off-state operation in a power electronics system) results in enhanced degradation (Figure 2) consistent with hole injection into the oxide. Varying degrees of degradation have been observed for devices exhibiting nearly identical initial characteristics, and we have identified a characteristic of the integrated free-wheeling diode that correlates with the observed degradation. For both gate stress polarities, the magnitude of threshold voltage shift increases with increasing temperature (Figure 3).

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Fig. 2. Post-stress (stress: Vg = -20 V @ 175 °C for 150 minutes) degradation in Id-Vg characteristics (Vd = 100 mV) of two nominally identical SiC MOSFETs.

Fig. 3. Vthreshold shift due to Vg = ±20 V gate stress for 30 minutes, plotted as a function of temperature. The device is recovered exactly to the initial state at the start of each bias step.

Devices were also stressed under pulsed

conditions at room temperature. Pulsed overcurrent operation (Figure 4a) showed degradation similar to what was observed under high-temperature, positive-Vg DC stress, consistent with electron injection into the oxide (Figure 1, positive voltage points on Figure 3). This may be due to transient heating of the device beyond the junction temperature specification (Tj = 125 °C). Figure 4b shows the transient current profile for a single switching cycle. The actual switching is preceded by a very high-current spike that lasts about

10 microseconds. This high-current transient is likely a significant factor in device degradation under pulsed overcurrent conditions, since for the same switching levels (Vg = +8 V, Vd = 20 V) 1-kilohertz (kHz) operation produces much faster degradation than 1-Hz operation.

Fig. 4. (a) Degradation in a SiC MOSFET due to pulsed overcurrent conditions, similar to the effects of positive gate bias DC stress at high temperature. (b) The high transient current peaks observed during switching are likely responsible for enhanced degradation at high switching frequency.

The effects of MOSFET device degradation on

system availability can potentially be mitigated through Condition Monitoring (CM) and Prognostics and Health Management (PHM). CM consists of monitoring component and/or system characteristics in situ to ascertain its health, and to detect anomalies and diagnose problems in order to flag maintenance needs. PHM goes further by not only tracking damage growth, but by also predicting time to failure (by comparing the state of the component to previously established reliability models), and by managing subsequent maintenance and operations in such a way to optimize overall system utility against cost. PHM seeks to optimize the trade-off between premature device replacement and disruptive failures. In our scenario, a well-developed method of CM and/or PHM can considerably increase the feasibility of exploiting the superior switching performance of the SiC MOSFET even before it reaches the level of technological maturity of Si-based devices (the latter

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has been studied and developed since the 1940s and has a several-decades head start over all competing technologies).

We have developed a 16-bit Microchip PIC [3]-based system to monitor the characteristics of the device while it is in operation. A current sense circuit uses a resistive network to perform a current-to-voltage conversion and communicates with the microcontroller through an opto-coupler (which is utilized to provide electrical isolation between the microcontroller and the power device). The setup has a built-in gate control circuit that uses the pulse-width-modulated (PWM) signal from the controller to provide a variable output to the gate. Figure 5 shows the output of our monitoring setup resulting from a slow voltage ramp applied to the gate of a SiC MOSFET biased at Vd = 5 V. The output current and threshold voltage match the device characteristics measured with standard laboratory equipment, showing a successful implementation of the most basic and vital block of the CM module. Measurements of this curve as the device is stressed, as well as efforts to increase the compactness and portability of the system, are currently in progress.

Fig. 5. Id-Vg curve of a SiC MOSFET, biased at Vd = 5 V, measured using our prototype microcontroller-based CM setup.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC0494AL85000. This work was performed under funding from the DOE Energy Storage Program managed by Dr. Imre Gyuk of the DOE Office of Electricity. We acknowledge Drs. David Grider, Mrinal Das, and Sarit Dhar of Cree for providing samples to us, and for useful discussions.

REFERENCES [1] A.J. Lelis, D. Habersat, R. Green, A. Ogunniyi, M. Gurfinkel, J. Suehle, and N. Goldsman, “Time Dependence of Bias-Stress-Induced SiC MOSFET Threshold-Voltage Instability Measurements,” IEEE Trans. Electron Devices 55, 2008, pp. 1835-1840.

[2] S. DasGupta, R. Brock, R.J. Kaplar, M.J. Marinella, M.A. Smith, and S. Atcitty, “Extraction of trapped charge in 4H-SiC metal oxide semiconductor field effect transistors from subthreshold characteristics,” Appl. Phys. Lett. 99, 2011, pp. 023503-023505.

[3] Microchip 16-bit Digital Signal Controller Product Datasheet, available online at http://ww1.microchip.com/downloads/en/DeviceDoc/70593B.pdf.

BIOGRAPHICAL NOTE Conference presenter: Robert Kaplar received a B.S. degree in Physics from Case Western Reserve University, Cleveland, Ohio (1994), and M.S. and Ph.D. degrees in

Electrical Engineering from Ohio State University, Columbus, Ohio (1998 and 2002). From 2002 to 2005 he was a Post-Doctoral Researcher at Sandia National Laboratories (SNL), Albuquerque, New Mexico. Since 2005 he has been a Senior Member of the Technical Staff at SNL. His current work focuses on semiconductor device characterization, reliability, and physics for Very Large Scale Integration (VLSI) and power device applications.

(a)

(b)

http://ww1.microchip.com/downloads/en/DeviceDoc/70593B.pdf

http://ww1.microchip.com/downloads/en/DeviceDoc/70593B.pdf

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125

SANYO’S SMART ENERGY SYSTEM WITH A 1.5-MEGAWATT HOUR LITHIUM-ION BATTERY AND 1-MEGAWATT PHOTOVOLTAIC SOLAR SYSTEM

Hiroshi Hanafusa

SANYO Electric Co., Ltd., Smart Energy System Division, Moriguchi, Japan

ABSTRACT

SANYO has developed a Smart Energy System (SES) that can generate, store, and consume green energy effectively and efficiently. At the SANYO Kasai Plant in the prefecture in Japan, we installed a 1-megawatt (MW) photovoltaic (PV) solar system, a 1.5-megawatt hour (MWh) lithium (Li)-ion battery system, energy management systems that efficiently control equipment, and an SES, which combines and coordinates all of these systems to maximize energy efficiency. The key component of the SES is the Li-ion battery system using 300,000 Li-ion cells typically found in laptop computers. The newly developed battery management system can control numerous cells as if they are just one single battery. We realize carbon zero-emissions in the on-site administration building and are able to reduce 15% peak demand of the whole factory by using our SES.

Keywords: battery management system, lithium-ion battery, solar

1. INTRODUCTION

Renewable energy such as photovoltaic (PV) and wind turbine generation is expected to play an important role for future energy solutions. Additionally, electrical energy storage is needed to stabilize the electricity grid fluctuation caused by the intermittent weather conditions as they relate to renewable energy sources. In order to become a leading company in the energy and environment business, the Panasonic/SANYO Group is promoting the development of new products and technologies. The aim is to help solve environmental and energy problems on a global scale with the company’s outstanding technological capabilities. In late 2010, SANYO set up a huge technology demonstration site in Kasai, using its own products such as PV panels, lithium (Li)-ion batteries, and newly developed energy management systems.

2. SMART ENERGY SYSTEM IN KASAI GREEN ENERGY PARK

In the Kasai Green Energy Park (Kasai GEP), we installed a 1-megawatt (MW) Mega Solar System, a 1.5-megawatt hour (MWh) Li-ion Mega Battery System, an energy management system that efficiently controls each piece of equipment, and a smart energy system (SES) that combines and coordinates all of the systems using an SES controller, as shown in Figure 1.

SESコントローラ

ElectricityEMS

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DC power Distribution

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Solar Charging Station

1M PV Solar System

Fig. 1. Construction of Smart Energy System.

By using all of these systems to maximize energy

efficiency, we are able to reduce approximately 2,480 tons of carbon dioxide (CO2) emissions every year without sacrificing any convenience. The core component of the SES is the SES controller. It monitors the conditions for electricity generation and storage with PV modules and storage batteries, while keeping track of the amount of electricity used by devices and equipment in real time. Through integrated control of technologies for energy generation, energy storage, and energy saving, the SES can use power efficiently without waste.

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3. CONSTRUCTION OF THE LI-ION BATTERY SYSTEM

The 1.5-MWh Li-ion battery system consists of a 1.3-MWh large-scale battery storage system using 240,000 pieces of 18650 standard cells and a DC distribution system from PV modules with 200-kWh Li-ion batteries. A new battery management system has been developed that deals with a large quantity of data such as voltage, current, and temperature for each cell instantaneously through advanced network technologies and then balances and controls each cell at the same time. This battery management system can control numerous cells as if they are just one single battery.

Fig. 2. Photo of Li-ion battery system in the energy storage building.

Figure 2 shows 1.3-MWh Li-ion battery system

in the energy storage building. Economical late-night electricity is mainly used to charge batteries. In order to ensure stable operation of the whole battery system, the Li-ion battery system consists of multiple elemental units that have 5 series-4 parallel of Li-ion boxes. A battery management unit controls 20 boxes. Each box has 312 pieces of 18650 cells. One series string consists of 5 units that have 160-kilowatt hours (kWh) and is connected to 1 power conversion system (PCS), as shown in Figure 3. The battery management unit (BMU) accurately detects the conditions for the Li-ion batteries based on the electric voltage, electric current, and temperature, and maximizes the performance of this large-scale storage battery as a whole.

Electricity EMS

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BMUBSU

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Data

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40 units

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Fig. 3. Configuration of the Li-ion battery system.

4. EFFICIENCY OF THE

LI-ION BATTERY SYSTEM Energy efficiency is critical when using a battery

system. In order to evaluate the actual efficiency of the Li-ion battery system, the comparison of electricity between input and output was measured.

Figure 4 shows transition of electricity through each device at the condition of SOC25%→SOC75%→SOC25%. Actual efficiency of the Li-ion battery system is about 98%; however, the efficiency of a PCS is about 94%, and the total efficiency after PCS is about 87%. It is still much higher than that of the NAS battery and lead-acid battery [1].

685.7kWh 650.5kWh 642.1kWh 640.3kWh 635.2kWh 595.3kWh

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Fig. 4. Transition of electricity through energy devices.

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5. DC POWER DISTRIBUTION THROUGH LI-ION BATTERY SYSTEM FROM PV SOLAR

Green buildings can take advantage of DC power distribution with PV generation (Figure 5).

Fig. 5. PV solar deployed vertically on the side surface of a building.

DC power from PV solar can be directly used in

DC devices such as LED lightning and laptops. Then, surplus DC power is stored in energy storage and provided to DC devices from storage at night. If PV solar generates more electricity, DC power is converted into AC power and consumed by AC devices. In the administration building, unconverted DC power from PV modules is the main source of electricity for charging batteries and direct consumption.

Fig. 6 shows the system configuration. A direct charging method from PV solar to Li-ion battery has been developed. Approximately 100% of the electric power consumed in the administration building can be offset by the electric power generated by all of the PV systems in the Kasai GEP and by the power consumption reduction effect of the Administration Building EMS.

Fig. 6. System configuration for DC power distribution.

6. PEAK SHAVING BY THE LI-ION BATTERY SYSTEM

Fig. 7 shows the total energy consumption data of the factory. The green part means the amount of energy saving by EMS, and the grey part is the electricity purchased from the grid. The SES can reduce demand charge by peak shaving. During daytime, PV solar generation, the orange part, saves the electricity purchased from the grid. However, PV solar could not provide enough electricity for peak shaving any more around 4 p.m., since our factory had the peak time around the sunset time. The SES controller decided to let the battery system discharge electricity to keep the peak load shaving. Then, the battery was charged using lower-costing electricity from the grid during the night. The SES reduced peak demand by over 15%. Our factory has a different peak time according to its production planning. Lots of operational patterns have been devised to determine when and how long the batteries have to charge and discharge. Kasai GEP is the ideal site to develop these kind of battery control technologies.

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00

Reduced electricity by EMSPV generationBattery chargeBattery dischargePurchased electricity

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ty C

onsu

mpt

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Fig. 7. Peak shaving by the SES.

7. CONCLUSION

The SES has proven to be useful for reducing carbon emissions and reducing peak demand without any inconvenience for employees or factory operation.

By making the energy usage conditions and facility information visible, the operations staff can identify inefficiencies and inconsistencies in factory and office energy use, and take actions to improve the environmental performance of the site. Furthermore, the staff can get a real sense of the site’s energy consumption visually through the large-screen displays installed around the site (Fig. 8), which will raise the employees’ environmental awareness at the Kasai GEP. indirectly leading to the reduction of CO2 emissions.

LiB

BMU

PV

DC/ DCconvertor

PCS ~AC/ DC

convertorLoad

（PC/ LED）96V 16/ 48V

AC 200Ｖ

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Fig. 8. Digital signage for the SES.

8. REFERENCES

[1] Research Institute on Building Cost, No. 68, pp. 70-73, 2010, http://www.ribc.or.jp/research/pdf/report/ report21.pdf;

9. ACKNOWLEDGMENTS The author would like to express his deepest

gratitude to all those who joined Kasai GEP project.

BIOGRAPHICAL NOTE Hiroshi Hanafusa joined the SANYO Electric Central Institute in 1981. He contributed to the development of semiconductors such as system LSI for digital camcorders for 10 years and acquired his doctor’s degree. He

acted as CCD general manager and various other administrative innovation project leaders. He was the project leader of new energy business development from April 2009, led the development of the SANYO Smart Energy System, and founded the Energy Solution Business Division, which is the previous body of the Smart Energy System Division of SANYO today.

http://www.ribc.or.jp/research/pdf/report/%0breport21.pdf

http://www.ribc.or.jp/research/pdf/report/%0breport21.pdf

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ULTRA-HIGH VOLTAGE SILICON CARBIDE THYRISTORS – NEXT-GENERATION POWER ELECTRONICS BUILDING BLOCKS

R. Singh and S.G. Sundaresan

GeneSiC Semiconductor, 43670 Trade Center Place, Suite 155, Dulles, Virginia, USA

ABSTRACT Advanced power electronics hardware requiring ultra-high-voltage (>6.5 kilovolts [kV]), high-current

(>50 amperes) switches have limited alternatives. Present silicon-based bipolar devices like insulated gate bipolar transistors (IGBTs), gate turn-off (GTO) thyristors, integrated gate-commutated thyristors (IGCTs), and emitter turn-off (ETO) thyristors suffer from low switching speeds, low junction temperature, poor paralleling behavior, lack of effective gate control, long repetitive recovery times (tq), and a low theoretical upper limit (~10 kV) of device voltage rating. Silicon carbide (SiC)-based double-junction injecting devices like thyristors have the potential to alleviate many of these limitations by offering lower VF, multi-kHz switching, and ease of paralleling since they require thinner/higher-doped epitaxial layers with smaller carrier lifetimes, and low intrinsic carrier densities to achieve a given device blocking voltage. These capabilities are expected to usher in a revolution in power electronics hardware for the utility grid, as well as pulsed power applications within the next decade.

Keywords: SiC thyristor, high-voltage, high-current, power conversion, utility grid

This paper outlines the progress on high-voltage

(≥ 6500 volts [V]) power silicon carbide (SiC) thyristor developments that is targeted at applications ranging from utility grid power conversion to pulsed power and high-temperature applications. Several flavors of SiC thyristor-based devices are presented to address the widely different performance metrics demanded by various application areas. Fast plasma spreading (FPS) thyristors are pursued for pulsed power applications requiring ultra-fast turn-on capability, while anode switched thyristors (ASTs) are developed for applications requiring ease of gate control and 5 to 10 kHz frequency operation. Detailed on-state, blocking voltage, turn-on, turn-off, and reliability metrics of the SiC thyristor-based devices are presented. A special focus of this paper will be the insertion of SiC thyristors in two diverse applications: a pulsed power circuit and a power converter test bench.

A number of key process steps including controlled slope SiC etching (Figure 1), precise edge terminations, surface passivation, and optimized metallization schemes were developed at GeneSiC in support of high-voltage SiC thyristor fabrication. As a result of numerous design and process innovations, near-ideal blocking voltages with low leakage currents at high temperatures (Figure 2) are recorded on packaged 6.5-kV SiC thyristors. A photograph of a

packaged 6.5-kV/40-ampere (A) SiC thyristor is shown as an inset in Figure 2. Nearly temperature-independent differential on-resistances as low as 2.5 mΩ-cm2 are extracted from high-current measurements (Figure 3) on large-area 28 mm2 and 77 mm2 SiC thyristors. A comparison with a commercial 4-kV Si thyristor (Figure 4) shows a smaller VF for the GeneSiC SiC thyristor at current densities > 430 A/cm2 on account of its lower on-resistance. The thyristor turn-on or turn-off is accomplished by switching the appropriate Si metal-oxide-semiconductor field-effect transistors (MOSFETs) on or off. In Figure 5, a cathode current of 28 A is turned off in ≈ 1 µs at 25 °C by the AST circuit. In Figure 5, a cathode current of 62 A flowing through a 77-mm2 SiC thyristor is turned off by the forced commutation technique by applying a reverse bias of +30 V to the cathode and maintaining a turn-off dI/dt of 405 A/µs. For a re-applied dV/dt of 520 V/µs, a minimum turn-off time (tq) of 6.3 µs needs to elapse before the thyristor is capable of supporting a forward blocking voltage without exhibiting a spurious turn-on by the dV/dt effect.

These demonstrations bode well towards adopting SiC-based thyristors as fundamental building blocks for advanced power electronics hardware for energy storage and smart grid applications

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Fig. 1. Cross-sectional SEMs of SiC Mesas etched with arbitrarily chosen sidewall slopes.

Fig. 2. Comparison of blocking voltages of GeneSiC’s SiC thyristor with a 4-kV Si thyristor.

Fig. 3. On-state I-V characteristics of large-area 77-mm2 and 28-mm2 6.5-kV SiC thyristors.

Fig. 4. Comparison of 25 °C on-state characteristics of GeneSiC’s SiC thyristor with a 4-kV Si thyristor.

Fig. 5. Reverse recovery characteristics of 77-mm2 Thyristor commutating 62 A at 405 A/µs by applying +30 V cathode bias. Minimum turn-off time = 6.3 µs.

Fig. 6. On-state voltage drop comparison between silicon and SiC bipolar devices for various utility voltages.

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BIOGRAPHICAL NOTE Dr. Ranbir Singh founded GeneSiC Semiconductor Inc. in 2004. He has developed critical understanding and published on a wide range of silicon carbide (SiC) power devices including PiN, JBS and Schottky diodes, metal-oxide-semiconductor field-effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), thyristors, and field controlled thyristors. He has co-authored over 110 publications in various refereed journals and conference

proceedings and is an inventor on 26 issued U.S. patents. He conducted research on SiC power devices first at Cree Inc., and then at the National Institute of Standards and Technology (NIST), Gaithersburg, MD. He received the B. Tech (Electrical Engineering) degree from the Indian Institute of Technology (IIT), Delhi, India. He received his M.S. and Ph.D. degrees from North Carolina State University (NCSU) under the tutelage of power device pioneer Prof. B. Jayant Baliga.

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Session 7 – Modeling and Simulation of EES

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135

WIDESPREAD DEPLOYMENT OF ELECTRIC STORAGE IN THE INDUSTRIAL AND MANUFACTURING SECTORS

Philip J. Scalzo

EMB Energy, Inc., Edmond, OK, USA

ABSTRACT An overview summary of a proprietary deterministic model developed to assess the intrinsic and extrinsic

values of electric storage deployed behind the fence at large industrial and manufacturing facilities is presented.

INTRODUCTION The electric industry has long recognized the

contribution that efficient and affordable electric storage will make toward maintaining grid reliability. Sandia National Laboratories’ (SNL’s) 2010 paper titled Energy Storage for the Electricity Grid Benefits and Market Potential Assessment Guide, A Study for the DOE Energy Storage Systems Program, SAND2010-0815, provides a “framework for assessing potential benefits from, and economic market potential for, energy storage used for electric-utility-related applications.” The SNL paper describes 17 applications for utility-scale electric storage, four of which relate to end user/utility customers. The SNL study utilizes a utility tariff (PG&E Tariff #E-19) to quantify the potential benefits of applying electric storage “behind the fence” of a utility customer qualified to take service from the utility under that tariff. The SNL report opens the door for a more extensive assessment of the key factors that will drive the large end user to make the commitment to install electric storage either independently or in collaboration with its utility provider.

DISCUSSION EMB Energy has developed a Microsoft Excel-

based deterministic model that evaluates the customer’s load profile both with and without electric storage and determines the optimal electric storage configuration to achieve maximum “intrinsic” economic benefit. Our “intrinsic value” model, as further described in this paper, seeks to answer the question, “What size electric energy storage deployment affords the best overall economic outcome to the industrial customer?” The model does not suggest alternative operating practices to the

customer. In other words, it will not suggest that the customer change its operating practices by curtailing demand during peak hours. It will, however, suggest alternative tariffs that may be offered by the utility to qualifying customers, but had been unavailable to the customer before the deployment of storage. Because the intrinsic value model is static, it can only take a “snapshot” in time. The model is indifferent to future facility demand growth (decline), power quality and reliability concerns, special conservation incentives, and future tariff rate adjustments. All of these factors, especially in the aggregate, will likely strongly influence any capital commitment decision.

As the SNL study recognizes, electric storage contributes to electric service reliability. A number of key factors relating to the operational capabilities of the storage technology, the sensitivity of the customer’s processes to interruptions, and the potential cost to the customer in terms of both lost product and downtime determine the full extent of that contribution. Our parametric stochastic (probabilistic) model describes this “extrinsic value” as a probability weighted distribution of net present values associated with the capital investment. This distribution of potential investment outcomes provides information not visible from the static intrinsic model; for example, it allows for an estimate of the probability that a project has a net present value greater than zero (or any other value). Our model, which employs classic Monte Carlo simulation techniques, allows the analyst to portray the company’s proprietary fundamental forecasts of the several exogenous and independent variables that should be factored into determination of extrinsic value as probability-weighted distribution rather than singular, discrete values. Since each probability-weighted distribution actually reflects the company’s

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uncertainty with respect to that variable input (i.e., decision criterion), “risk adjustment” is effectively achieved simply by running the simulation many times and presenting the outcome, itself, as a distribution.

CONCLUSIONS The combination of the intrinsic benefits of

reduced demand charges and overall lower energy costs, and the extrinsic benefits of improved electric service reliability, will create the incentive for end users/utility customers to install electric storage. Progressive electric utilities will collaborate with their large industrial and manufacturing customers and their regulators to implement new tariffs that share both the costs and benefits of distributed electric storage. An overview summary of the multiple synergies that can be exploited through cost and benefit sharing is also presented.

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MODELING OF PV PLUS STORAGE FOR PUBLIC SERVICE COMPANY OF NEW MEXICO’S PROSPERITY ENERGY STORAGE PROJECT

O. Lavrova,1 F. Cheng,1 Sh. Abdollahy,1 A. Mammoli,2 S. Willard,3 B. Arellano,3 and C. van Zeyl4

1Department of Electrical and Computer Engineering, 2Department of Mechanical Engineering, University of New Mexico, Albuquerque, NM, USA

3Public Company of New Mexico (PNM), 4East Penn Manufacturing

Keywords: battery management system, photovoltaics, solar intermittency, load shifting, demand response

INTRODUCTION

At the Public Service Company of New Mexico (PNM), in collaboration with other partners (Electric Power Research Institute [EPRI], University of New Mexico [UNM], East Penn Manufacturing Inc. [EPM], Sandia National Laboratories, and Northern New Mexico College), a demonstration project is under way that will couple an advanced lead acid battery with the output of a 500-kW photovoltaic (PV) installation. The main objectives of this demonstration project are two-fold: (1) demonstration of power peak shifting from the typical mid-day peak by planned (“slow”) action from the battery, and (2) simultaneous smoothing of the PV plant output by fast-response counteraction from the battery. The system has been rigorously modeled (using GridLAB-D™ software) in order to derive the optimal load shifting and smoothing algorithms that lead to the optimal Levelized Energy Cost (LCOE) as well as optimal lifetime of the battery. Once installed, the system will be tested in various configurations to validate or correct predicted models starting from 2011 Q4.

System Description

The system is located at New Mexico’s Mesa del Sol, a sustainable master-planned community that will contain different types of distributed energy resources such as PV, fuel-cell, co-generation, and the EPM shifting/smoothing storage system, which is the subject of this paper. The residential part of Mesa del Sol is also a state-of-the-art smart grid community. Houses will be equipped with smart meters and a significant percentage of them will have PV generation. Additional provisions will be taken with the expectation of significant percentage of electric vehicle ownership.

The EPM system combines two technologies to provide 0.5-megawatt (MW) smoothing capacity and

1-megawatt hour (MWh) storage capacity. The first technology is the UltraBattery, which is a valve-regulated lead-acid (VRLA) battery exhibiting ultra-capacitor features for rapid discharge applications. The second is the Advanced Carbon Battery, which is a VRLA battery exhibiting significantly longer cycle life than standard VRLA technology. The combination of these two battery technologies enables long-life VRLA batteries to be deployed with solar PV power plants to both smooth power generation that is interrupted by variable clouds, and shift power generation to times of high power demand. A power system one-line of the bulk electric system (BES) in combination with the 500-kW solar PV power plant is shown in Figure 1.

MODELING AND RESULTS GridLAB-D™, developed by Pacific Northwest

National Laboratory (PNNL) for the Department of Energy (DOE), was identified as a software platform used for modeling of our system. GridLAB-D is an open-source agent-based power distribution system simulation and analysis tool designed specifically for analyzing smart grids with decentralized control. GridLAB-D™ can also be integrated with a variety of third-party data management and analysis tools. Additional conversion software for exporting utility’s infrastructure (from databases such as ARC-GIS) had to be developed by UNM. Additionally, special care was taken to develop the battery model because any large-scale battery is not a standard battery module included in the software.

Two distinct cases for optimization were evaluated: when charging at night is allowed (“any” electrons) or when charging is restricted to charging from the local PV source only (“green” or “renewable” electrons only). Although charging from the “renewable” electrons is one of the goals, it is intuitive that charging at night from

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“any” electron mix is a cheaper solution at the current state of utilities. Figure 2 shows an example of load shifting for these two cases. Since charging only from a PV source is allowed for the “green” electrons, no additional load is experienced for charging the battery during the off-peak hours.

Several scenarios with different parameters to be optimized have been considered. Of primary importance are reduction of the peak load on the feeder during Albuquerque peak load time, and evaluation of cost-efficiency of the battery for load shifting application. A number of criteria were used to estimate cost-efficiency. One of the ways to quantify cost-efficiency is to normalize the cost savings to the capacity of a feeder [1]. Figure 3 shows two plots representing results of such comparison for summer and winter seasons for the “green” electrons case. Peak shifting proved to be approximately twice more cost-effective in summer months than in winter.

CONCLUSIONS We present results of modeling of various scenarios

of advanced lead-acid battery with the output of a 500-kW PV installation. For each scenario, a number of benefits is evaluated and compared, taking into account battery cost and finite lifetime. We present a detailed description of modeling and results of the LCOE analysis.

ACKNOWLEDGMENTS This work was supported in part by the following

grants: EPRI P.A. EP_P32412/C15054 and DOE –PNM DE-OE000230

REFERENCES [1] “Statewide Joint IOU Study of Permanent Load Shifting,” a report Prepared for Southern California Edison, Pacific Gas and Electric, San Diego Gas and Electric, December 1, 2010, CALMAC Study ID SCE0292.01.

Fig. 1. One-line diagram of the solar PV power plant integrated with the BES.

500kWp Solar

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BIOGRAPHICAL NOTES Conference presenter: Olga Lavrova (SM 2000, M 2011) was born in St. Petersburg, Russia. She received her B.Sc. degree in Physics and M.Sc. degree in Electrical Engineering from the St. Petersburg State Electrical Engineering University, and her Ph.D. degree from the University of

California at Santa Barbara (UCSB) in 2001. Her employment experience includes postdoctorate research at UCSB, as well as working in the areas of optoelectronic devices at two startup companies and a major corporation (Emcore Corporation). She joined the University of New Mexico in 2007 as a Research Professor, and is now Assistant Professor at the Electrical and Computer Engineering Department. Her current work and areas of interest include photovoltaics and

nano-scale semiconductor structures for photovoltaic applications, smart grids, and emerging energy generation, distribution, and storage technologies.

Feng Cheng was born in Shanxi, China. She graduated from Beijing Jiaotong University in 2007 with the major of power system and automation. Now she is pursuing her Ph.D. in electrical and computer engineering at the University of New Mexico. Her research

interests are in the area of smart grids and renewable energy.

Shahin Abdollahy (SM 2011) received the B.Sc. degree in electrical engineering from IUT, Isfahan, Iran, in 1998 and the M.Sc. degree in electrical engineering from Tehran Polytechnic, Tehran, Iran, in 2000. He worked in industry from 2000 to 2009

Fig. 2. Two cases of load shifting, when charging from the grid (or “any” electrons) is allowed (a), or when charging from only PV (“green” electrons) is allowed (b).

(a) (b)

Fig. 3. Comparison of avoided cost normalized by the peak capacity reduction per hour for the case of “green” electrons for summer (a) and winter (b) for different shift durations and start times.

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in drives and power converters design as senior design engineer and R&D manager. He is currently pursuing a Ph.D. in electrical engineering at the University of New Mexico, Albuquerque, NM, USA.

Andrea Mammoli was born in Ancona, Italy. He graduated with a Bachelor of Engineering in 1991 and a Ph.D. in 1995 from the Department of Mechanical & Materials Engineering at the University of Western Australia.

He was a Director Funded Postdoctoral Fellow at Los Alamos National Laboratory from 1995 to 1997. He subsequently joined the University of New Mexico as a research faculty member, and is now Associate Professor in Mechanical Engineering and co-Director of the Center for Emerging Energy Technologies. His current research deals with the integration of building-scale energy systems with the electricity grid, particularly as applied to energy storage and distributed systems management. Mammoli is Regents' Lecturer and Halliburton Professor at the University of New Mexico. His projects received several awards, including the Association of Energy Engineers Region 4 Renewable Energy Project of the Year in 2009 and the GridWise Architecture Council’s GridWise Applied Award in 2008.

Steve Willard, Professional Engineer, currently serves as the Principal Investigator for PNM’s Smart Grid Demonstration Project with the Department of Energy. He has more than 25 years’ experience in the energy

industry in regulated and unregulated markets, including product development and support, energy system engineering and analysis, as well as energy industry market research. Previous positions include Manager of the Center for Innovation and Technology at PNM, Product Support Manager for Honeywell Power Systems, Lecturer in the U.S. Peace Corps, and Computer Applications Engineer at Bridgers and Paxton Consulting Engineers Inc. Mr. Willard holds two U.S. Patents, BSME and MBA degrees (both from the University of New Mexico), and is a licensed engineer in the State of New Mexico.

Brian Arellano was born in Farmington, New Mexico. He graduated from the University of New Mexico in 2006 with a Bachelors of Science in Electrical Engineering.

His employment experience includes Geographic Information Systems Technical Supervisor with Public Service Company of New Mexico (PNM), Distribution Engineer with PNM, Santa Fe Division in Northern New Mexico, and continuing as an Advanced Technology Project Manager with PNM Resources. His special fields of interest include smart grid technology in the utility industry along with process improvements using Lean and Six Sigma Methodology. He is currently working on an Energy Storage Research and Development Project supported by the DOE. Project partners of this project include the University of New Mexico, as well as Sandia National Laboratories providing support for data modeling and analysis.

Mr. Arellano received nominations and has been accepted for the advisory boards of two organizations as the PNM representative: STEM, which promotes Science, Technology, Engineering and Math Education in New Mexico; and the New Mexico Engineering Foundation (NMEF), which promotes the advancement of engineering education and conducts and support educational programs in engineering.

Clemens van Zeyl, MBA, Professional Engineer, has a diverse range of experience as a senior executive in multiple engineering and technology firms. In the span of 30 years, through various roles in the industry, Mr. van Zeyl has been

a visionary in the implementation and commercialization of advanced technological products. His multifaceted expertise is demonstrated by his success in the starting, growing, and repositioning of companies. Product introduction, marketing, operations efficiency, and financing are more than familiar to Mr. van Zeyl. Before forming vZenergy, he successfully led research and development projects for such Fortune 500 companies as GE and Shell, and was crucial in bringing multiple innovative products into the market. Mr. van Zeyl’s ability to pair technical know-how with sharp business acumen allowed him to facilitate multimillion dollar agreements with leading technological manufacturers and government agencies.

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OPTIMIZATION ROUTINE FOR ENERGY STORAGE DISPATCH SCHEDULING IN GRID-CONNECTED, COMBINED PHOTOVOLTAIC-STORAGE SYSTEMS

Anders Nottrott, Jan Kleissl, Ph.D., and Byron Washom

University of California San Diego, Department of Mechanical and Aerospace Engineering, La Jolla, CA, USA

Ongoing advances in electrochemical battery

technologies have dramatically increased the energy density, reliability, and product lifetime of batteries. These improvements have translated to significant cost reductions in kilowatt (kW)-scale batteries, making battery energy storage an attractive option to regulate the variable power output of photovoltaic (PV) systems. If a battery is connected to the PV system behind the grid interconnect, the energy stored in the battery can be dispatched “on demand” to modulate the net output of the combined PV-storage system (hereafter PVS system) to the grid.

We considered a simplified PVS system, in which a PV array and a battery are connected to the electricity grid via a lossless DC-AC inverter (see Figure 1). The goal is to determine the optimal energy dispatch schedule for the battery to achieve load peak shaving, such that the net PVS system power output meets or exceeds the customer load peak. The optimization algorithm leverages day-ahead PV power output and load forecasts (with 15-minute resolution and 3-hour updates) to ensure that the customer load peak is eliminated or reduced as much as possible, subject to electrical performance constraints of the battery array. Our model provides a convenient framework to quantify the financial value of solar forecasts. In this paper we simulated the optimal storage dispatch schedule for a typical commercial-scale PVS system during one year, and compared the optimal scenario to a simple off-peak/on-peak, charge/discharge dispatch schedule that was generated without any knowledge of future PV power output or customer load (Figure 2). Our analysis shows that the application of solar forecasting to the energy storage dispatch problem results in significant financial savings when compared with a simple off-peak/on-peak scenario (Table 1). Financial savings are realized from a combination of demand charge reduction, time-of-use price arbitrage and reduced battery cycling, which results in extended battery lifetime.

Fig. 1. Schematic of the model system illustrating the important components and power flows. All power electronics and wired connections are assumed to be 100% efficient and the battery output response is nearly instantaneous (i.e., the response time of lithium (Li)-ion type batteries is on the order of milliseconds while energy dispatch is modeled on 15-minute intervals). Because we have assumed the inverter to be lossless it is not shown in this diagram. The battery management system is included in the battery, which allows “black box” treatment of complex electrical dynamics and transients within the battery.

We applied a nonlinear, mathematical

programming routine with receding horizon optimization to compute the optimum dispatch schedule for the energy stored in the battery. Equations 1, 2a-c, and 3a-c are the objective function, system dynamics, and battery performance constraints, respectively.

𝑚𝑖𝑛 𝑓(𝑃𝑙𝑓𝑛 ,𝑃𝑜𝑛) = (𝑃𝑙𝑓𝑘 − 𝑃𝑜𝑘)∆𝑡𝑁

𝑘=1 ,𝑤ℎ𝑖𝑙𝑒 𝑃𝑙𝑓𝑘

≥ 0 𝑎𝑛𝑑 𝑃𝑙𝑓𝑘 > 𝑃𝑝𝑓𝑘 𝑠. 𝑡.

(1)

𝑃𝑝𝑓𝑛 + 𝑃𝑠𝑛 = 𝑃𝑜𝑛 (2a) 𝐸𝑛+1 − 𝐸𝑛

∆𝑡 = 𝑃𝑛 (2b) 𝑃𝑛+1 − 𝑃𝑛

∆𝑡 = 𝑅𝑛 (2c)

𝐸𝑠𝑚𝑖𝑛 ≤ 𝑃𝑠𝑘𝑛

𝑘=1+ 𝐸0 ≤ 𝐸𝑠𝑚𝑎𝑥 (3a)

𝑃𝑠𝑚𝑖𝑛 ≤ 𝑃𝑠𝑛 ≤ 𝑃𝑠𝑚𝑎𝑥 (3b) 𝑅𝑠𝑚𝑖𝑛 ≤

𝑃𝑠𝑛+1 − 𝑃𝑠𝑛

∆𝑡 ≤ 𝑅𝑠𝑚𝑎𝑥 (3c)

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(a)

(b)

Fig. 2. Typical PVs power flows on October 31, 2009. (a) The optimal storage dispatch schedule from the model described in Equations 1, 2, and 3; (b) the simple off-peak/on-peak, charge/discharge schedule that does not use solar or load forecasts. The PVS output (dashed red line) closely follows the customer peak load curve (blue line) in (a) but the PVS output falls short of the customer peak load in (b). This example indicates superior performance of the optimal scenario and demonstrates the advantages of applying the solar forecast to determine the stored energy dispatch schedule. Dashed lines show the limits of the battery charge/discharge power.

Variables E, P, and R are energy, power, and

ramp rate. Variables with subscript s are related to the battery array, subscript pf refers to the PV power output forecast, subscript lf is the load forecast, subscript o denotes power flows to and from the grid, and 0 indicates an initial condition. Superscript n is

the current timestep and N denotes the maximum number of timesteps over the forecast horizon (i.e., N = 96 for a 24-hour forecast horizon at a 15-minute sampling rate). Superscripts min and max indicate performance limits of the battery.

An idealized PV output forecast was obtained from one year of 15-minute DC power output data from the EBU2 rooftop PV array on the University of California, San Diego (UCSD) campus. The PV array has a DC nameplate rating of 75 kW DC. A load forecast was generated from UCSD campus historical load data. Uncertainty in the load forecast was simulated by incorporating random, normally distributed fluctuations with a standard deviation of 5% of the magnitude of the peak load at any given time. To simplify the analysis, weekend and holiday loads were not considered in this paper. The desired amount of customer peak load reduction (based on the load forecast) is a parameter in the model and was set to 150 kW for the results presented herein. The energy storage device was a Sanyo DCB-102 Li-ion type battery array consisting of 120 DCB-102 batteries. A single Sanyo DCB-102 is specified to have an energy storage capacity of 1.59 kW a lifetime of 3000 cycles at 80% depth of discharge (DoD). The retail cost was assumed to be $1000/kWh. The battery array has a total energy storage capacity of 𝐸𝑠𝑡𝑜𝑡𝑎𝑙 = 190 kWh and a maximum charging power 𝑃𝑠𝑚𝑖𝑛 = 41.2 kW and discharging power 𝑃𝑠𝑚𝑎𝑥 = 86.6 kW. To avoid overcharging or overdrawing of the battery array, the model parameters 𝐸𝑠𝑚𝑎𝑥 and 𝐸𝑠𝑚𝑖𝑛 are set to 0.2𝐸𝑠𝑡𝑜𝑡𝑎𝑙 and 0.99𝐸𝑠𝑡𝑜𝑡𝑎𝑙, respectively. Power requirements for active cooling of the battery array are not considered in the model.

Utilities assess time-of-use (TOU) energy pricing and demand charges for industrial customers. We performed a basic cost analysis to compare relative benefits of the optimal dispatch scenario and the off-peak/on-peak dispatch scenario. The customer’s monthly energy bill was calculated for one year using the San Diego Gas & Electric (SDGE) AL-TOU rate schedule for industrial customers. The AL-TOU schedule includes basic service fees, seasonal and peak demand charges, and TOU energy pricing. Table 1 shows the results of the cost analysis and illustrates significant advantages of the application of solar forecasting in peak-shaving applications. The financial value of the solar forecast can be quantified in terms of the difference between profits to the PVS system owner at the end of the system lifetime under the two scenarios. For this case the value of the solar forecast was approximately $116,000.

305 305.2 305.4 305.6 305.8 306-50

0

50

100

150

200

Ordinal Date in 2009

P [k

W]

PpfPlfPsPo

305 305.2 305.4 305.6 305.8 306-50

0

50

100

150

200

Ordinal Date in 2009

P [k

W]

PpfPlfPsPo

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Table 1. Cost analysis comparison of optimized dispatch schedule with the PV power output forecast and simple off-peak/on-peak dispatch schedule without the PV power output forecast. The value of the solar forecast is about $116,000 based on the difference between the profits associated with each scenario. The battery lifetime increased by 173% under the optimized dispatch scenario relative to the simple off-peak/on-peak scenario.

Optimization with PV Power

Output and Load Forecast

Off-Peak/On-Peak without

PV Power Output and

Load Forecast Annual Energy Bill Cost Reduction [$] 33,200 29,200

Number of Cycles at 80% DoD [cyc/yr]

420 730

Battery Lifetime [yr] 7.1 4.1 Fixed Cost Simple Payback Time [yr] 5.7 6.5

Total Profit at End of Battery Lifetime (Annual Energy Bill Savings x Battery Lifetime – Fixed Costs) [$]

45,300 – 70,700

BIOGRAPHICAL NOTE Conference presenter: Byron Washom is the University of California at San Diego’s (UCSD’s) new Director of Strategic Energy Initiatives and is responsible for energy management policy to achieve the campus' goals for quantum improvements in energy management and greenhouse gas

reductions. Before UCSD, Mr. Washom was the CEO for 20 years of a due diligence firm that specialized in CleanTech, and he served as Senior International Advisor to the World Bank and the Department of Energy. He is a four-time Rockefeller Foundation Grantee and a former Heinz Endowment Grantee for early commercialization of CleanTech into developing countries. Mr. Washom was also Founder and President of Advanco Corporation, which in 1984 set the long-standing world records for solar electric conversion efficiency at 29.4% and subsequently achieved an IR100 Award. He was the 2008 Recipient of UCSD’s Citizen of the Year Award for Sustainability, and he was a Visiting Faculty Member at the Rady School of Management while teaching the graduate-level course, The Business of Renewable Energy. Fast Company magazine named him to their June 2010 cover story, “100 Most Creative Persons in Business, 2010.”

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NUMERICAL ANALYSIS ON THE TEMPERATURE DISTRIBUTION

IN THE MOLTEN SODIUM-SULFUR BATTERY MODULE

June Kee Min1 and Chang-Hui Lee2

1Pusan National University, Busan, Korea 2Research Institute of Industrial Science and technology, Pohang, Korea

ABSTRACT

The sodium-sulfur battery cell operates at a high-temperature condition of 290 oC to 350 oC to use molten-liquid-state electrodes. The battery module consists of multiple cells and the corresponding thermal management system such as heaters and insulations. The optimal design of the thermal management system is essential in order to achieve uniform temperature distribution inside the module, and the overall energy efficiency of the module is directly dependent on the heat dissipation of the casing. In the present study, a new numerical model for the thermal analysis of sodium-sulfur battery module has been suggested. The heat generation of the cell was modeled based on the electrochemical reaction process of the battery. The thermal properties of the cell such as thermal conductivity and thermal capacity were also modeled by using the one-dimensional thermal network analysis and available test results. Using these equivalent thermal models of the cell, the three-dimensional temperature distribution inside the battery module could be predicted by solving the thermal energy conservation equation numerically. The distribution of temperature and the thermal energy efficiency of the battery module for different arrangements of the cells and heaters are summarized.

Keywords: sodium-sulfur battery, thermal management, numerical analysis

INTRODUCTION

It is well known that the sodium-sulfur battery has a high energy density, high efficiency of charge/discharge, and long cycle life. In 1960s, studies on this battery for the application to the electric car were carried out. Since the 1980s, this battery has been a promising candidate for the stationary energy storage. Great achievements have been made for this application, especially in Japan and Europe [1].

The sodium-sulfur battery operates at a high-temperature condition of 290 oC to 350 oC to use molten-liquid-state electrodes. The battery module, which contains multiple unitary cells, uses the thermal management system such as the heater and the insulation casing. This thermal management system should be able to heat the battery to desired temperature and maintain an even temperature distribution in all operating conditions [2]. The heat dissipation from the module is also important since it is directly related to the module efficiency [3]. As a result, the optimal design of the thermal

management system for the battery module is essential.

In the present study, the numerical prediction model of the sodium-sulfur battery module has been suggested. Even with the rapidly growing computer capability, the direct prediction of thermal performance of the battery is too complicated. To overcome this complexity, a multi-level approach has been adopted by evaluating equivalent thermal properties of the cell. Furthermore, a multi-fidelity approach that incorporates zero- and three-dimensional analyses has also been developed.

NUMERICAL APPROACH Cell Model

Figure 1 represents the typical configuration of a sodium-sulfur cell. The purpose of cell model analysis is to get equivalent thermal properties such as the thermal conductivity, specific heat, and density in order to use in the module-level analysis. From the geometric configuration of the cell, the thermal conductivity of the cell should have

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different values in the horizontal and vertical directions, respectively. For a numerical thermal analysis, hexahedral mesh was generated inside the half model of the cell. Figure 2 shows the temperature distributions inside the cell when it is under temperature difference. As a result, the equivalent anisotropic thermal conductivities in each direction can be evaluated by solving the Fourier’s law using the calculated heat transfer rate Q. The other properties are calculated considering the volume fractions of each component inside the cell.

Module Analysis

Figure 3 shows the quarter model of sodium-sulfur battery module. In the module analysis the cell is assumed to have equivalent thermal properties evaluated in the cell model. The gap

between the cells is filled with the industrial sand. It is known that the heat generation inside the cell can be represented by the following equation.

dEQ I TdT

η = −

(1)

In the above equation, the first term represents the joule heating due to the electric resistance of the cell and the second term is an entropy term that represents the heat of reaction. The chemical reaction of the sodium-sulfur cell is exothermic for discharge and endothermic for the charge process. In the present study, the experimental correlation of the entropy generation by Koendler [4] has been used in the calculation. Using computational mesh generated inside the module, the unsteady heat conduction equation is solved to get the temperature distribution.

RESULTS

In Figure 4, the temperature distribution inside the battery module is depicted at the end of discharge period. In the calculation, it is assumed only the heaters at the side and bottom walls were working. It can be seen that the cells near the heater have higher temperature and the non-uniformity of temperature can be precisely evaluated quantitatively. Due to the heat generation inside the cell, the cell shows relatively higher temperature compared to the surrounding sand region. Figure 5 shows the variations of average, maximum, and minimum temperatures for module operation. It is expected that the optimal design of the thermal management system for the sodium-sulfur battery module can be carried out numerically by using the suggested procedure.

Fig. 1. Schematic of a sodium-sulfur cell.

Fig. 2. Temperature distribution inside the cell.

Fig. 3. Solid model of a battery module (1/4).

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REFERENCES [1] Z. Zhaoyin et al., “Research on sodium sulfur battery for energy storage,” Solid State Ionics 179, 2008, pp.1697-1701.

[2] G. Eck, “Design of the thermal management systems for sodium-sulfur traction batteries using battery models,” Journal of Power Sources 17, 1986, pp. 226-227.

[3] R. Okuyama et al., “Relationship between the total energy efficiency of a sodium-sulfur battery system and the heat dissipation of battery case,” Journal of Power Sources 77, 1999, pp. 164-169.

[4] R. Knoedler, “Thermal properties of sodium-sulphur cells,” Journal of Applied Electrochemistry 14, 1984, pp. 39-46.

BIOGRAPHICAL NOTE Conference presenter: Dr. Min is a research professor at Rolls-Royce University Technology Center in Thermal Management at Pusan National University, South Korea. He studied at Korea Advanced Institute of Science and Technology

(KAIST) for his B.S. degree and at the Seoul National University (SNU) for his Ph.D. and M.S. degree. Before he joined Pusan National University, he worked for the LG Electronics and Samsung Electronics as a thermo-fluid engineer for more than 10 years. His research interests mainly include compressed air energy (CAE)-based heat transfer problems for advanced thermal management systems.

Fig. 5. Temperature variation inside the module.

Fig. 4. Temperature distribution inside the module.

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Poster Session 2

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HYDROGEN ENERGY STORAGE

Erik Wolf

Siemens AG, Energy Sector Renewable Energy

Great portions of renewable energy in a future

energy supply system lead to a dramatically altered layout and mode of operation of the whole system. To ensure the economic efficiency of the system, cost-optimizing solutions need to be searched for.

These very complex questions of layouts can be calculated today with appropriate methods. One receives a resilient image of the infrastructure needed, especially the capacity of the energy transmission network and of the necessary backup power plants. Moreover, the efficiency and mode of operation is determined by large energy stores, from which, in the end, political and technical operational recommendations are being derived.

Fig. 1. Example storage demand for Europe is determined by the generation mix (a: wind power; b: solar and other available sources; c: conventionally also biomass or geothermal energy).

The challenge of an energy supply system fed by a

100% renewable source of energy is the possibility to use the surplus production of electric energy in times of underproduction. Energy storage with high capacity

and output power are needed for compensation purposes. In reference to the previously explained storage needs (Figure 1), it is displayed how with the help of hydrogen and conventional gas power plant technology a storage can be put to use to cover large production deficits with an output of ~500 MW und >100 GWh (equals a week of base load operation).

Large energy storage (see Figure 2) is important for areas of high population density and cities with high demand in energy. For smaller communities, smaller systems (<100 MW) in form of daily storages are also being discussed and will be addressed in the lecture. They would enable an autarky without recourse to the network as backup.

Apart from these two qualities, output, and capacity provision, another technical aspect will be discussed: the stabilization of the network (short circuit strength) with the help of this storage technology.

A brief economic view on the investment, as well as the operation and electricity cost, will complete the introduction of this technology.

Fig. 2. Hydrogen large-scale energy storage.

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SILICON NANO-SCOOP ANODES FOR HIGH-POWER LITHIUM-ION BATTERIES

Nikhil Koratkar

Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA

Keywords: lithium-ion batteries, high power/rate capability, C-Al-Si nanoscoops, functionally strain-graded materials

Lithium-ion batteries show poor performance

for high-power applications involving ultrafast charging/discharging rates. Here we report a functionally strain-graded carbon-aluminum-silicon (C-Al-Si) anode architecture that overcomes this drawback. It consists of an array of nanostructures each comprising an amorphous carbon nanorod with an intermediate layer of Al that is finally capped by a Si nano-scoop on the very top. The gradation in strain arises from graded levels of volumetric expansion in these three materials on alloying with lithium. The introduction of Al as an intermediate layer enables the gradual transition of strain from C to Si, thereby

minimizing the mismatch at interfaces between differentially strained materials and enabling stable operation of the electrode under high-rate charge/discharge conditions. At an accelerated current density of ~51.2 A/g (i.e., charge/discharge rate of ~40 C), the strain-graded C-Al-Si nano-scoop anode provides average capacities of ~412 mAh/g with a power output of ~100 kW/kgelectrode continuously over 100 charge/discharge cycles. A paper related to this work was recently published in Nano Letters (R. Krishnan, T.-M. Lu, and N. Koratkar, “Functionally strain graded nanoscoops for high power Li-ion battery anodes,” Nano Letters, 2011, dx.doi.org/10.1021/nl102981d).

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ECONOMIC AND COST MODELING OF THE REPURPOSING OF ELECTRIC

VEHICLE BATTERIES FOR STATIONARY STORAGE APPLICATIONS

Sam Jaffe

IDC Energy Insights, Boulder, CO, USA

ABSTRACT

Lithium (Li)-ion batteries represent a tremendous opportunity for vehicular and grid storage applications. When measured against other battery chemistries, Li-ion excels at high energy and power densities, while cycling at high efficiencies over long periods of time. Their primary weakness is the high manufacturing cost, which should come down over the next five years as manufacturing plants scale up. However, additional value and lower prices can be achieved if the Li-ion batteries are repurposed after their useful life in vehicles for other applications, primarily grid storage. This poster examines the chemistry and the economics behind repurposing vehicular battery packs for grid storage applications and includes a model for pricing the batteries and the impact of repurposing strategies on both the vehicular application and the grid storage application.

Keywords: battery management system, lithium-ion, EV batteries, grid storage

GENERAL

In the race to determine the next-generation battery that is optimal for use in electric vehicles (EVs) and in grid storage applications, it is now clear that Lithium (Li)-ion has won the first few laps. Due to the excellent efficiency profile, energy density, power density, cycle life, and calendar life, Li-ion is able to outperform most other chemistries. Its primary drawbacks are safety (due to the possibility of thermal runaway) and manufacturing cost. Due to next-generation formulations, Li-ion batteries have proven that they can solve the safety issues that have hampered previous iterations of the technology.

Additionally, the Li-ion manufacturers are making good progress at cutting manufacturing costs to the point where IDC Energy Insights predicts that cells will reach the $500 per kilowatt hour (kWh) threshold sometime in the next three years. However, advancements beyond that point will be hard to make. It is hard to determine a route that Li-ion manufacturing can take to get prices significantly below $400/kWh.

Repurposing Li-ion batteries in order to lengthen their useful lifetime and thereby reduce the overall cost of the cells (thanks to a resale value of the used batteries for the initial buyer and a deeply

discounted value for the second buyer) allows for a further reduction in the cost of the batteries.

The concept of repurposing batteries introduces several potential problems, however, including:

• The initial buyer of the battery system (the automotive original equipment manufacturer) has to pay careful attention to the care and conditions of the battery during its lifetime in the vehicle than it would otherwise be required to if it assumed that the battery were to be disposed of after being taken out of the car.

• The secondary buyer (the electric utility) must change its cultural predisposition to purchasing used equipment, something which is very rarely done today.

• The battery pack for the vehicle must be designed for the easy refurbishment of cells upon repurposing, rather than being solely designed for the optimization of the driving experience.

• A method for replacing failed cells within a module or pack should be made possible, which is not the case today due to adhesives that hold the cells together.

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• Thermal management systems, power electronics, and battery management systems for the repurposed modules must be designed for specific grid applications.

Assuming that sufficient solutions for each of

the above problems can be achieved, then repurposing batteries can become an active part of both the EV ecosystem and of the grid storage ecosystem.

It's also important to determine how much such batteries could cost the secondary buyers. Assuming that a $400 per kWh price point is achieved by 2020 (when the first large volumes of batteries will start to come out of cars), the residual value of battery packs must be priced at a steep discount to the new packs that will be available at that time. According to modeling done by IDC Energy Insights, it is realistic to expect that the repurposed battery packs will have a residual value of at least $100 per usable kWh and as much as $150 per usable kWh.

The implications of that price range are significant for both the EV industry and the grid storage industry. The cost of a new battery pack for an EV will effectively be $250 to $300 per kWh at the cell level, which makes plug-in electric vehicles (PEVs) extremely price competitive with internal combustion vehicles. Likewise, a $100 to $150 per kWh price point for grid storage batteries enables them to be utilized for a wide range of applications, ranging from ancillary services to demand response to possibly even bulk load shifting.

While repurposing of grid storage batteries is still a decade away, it is important for both the PEV industry and the grid storage industry to begin the strategic planning process for utilizing this process to make Li-ion batteries usable for both industries.

BIOGRAPHICAL NOTE Sam Jaffe is responsible for researching, writing, and editing qualitative and quantitative reports and presentations evaluating a range of distributed energy topics. His recent research includes reports on the utility industry’s response to the rollout of electric vehicles, an analysis of the concept of the virtual power plant, and an overview of the energy storage sector. In addition to primary research authorship, he provides custom consulting, advisory, and research services for clients, most of whom are executives in the utility industry and vendors that sell into that industry. He also gives public talks at industry events and is frequently quoted in the media.

Before joining IDC Energy Insights, Mr. Jaffe ran his own consulting company, Panea Energy, which specialized in providing business development advice and consultation in the energy storage and renewable energy fields. Before Panea Energy, Mr. Jaffe was a magazine journalist, writing for such publications as Wired, Scientific American, The Scientist, Business Week, and The Wall Street Journal. He is the author of two books, Jewish Wisdom for Business Success (2008) and The New Korea (2010), both published by Amacom, the publishing arm of the American Management Association. He received a B.A. degree from Wake Forest University and an M.A. degree from New York University.

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EXPERIMENTAL APPROACH FOR THERMAL MODELING OF

SODIUM-SULFUR BATTERY BASED ON ISOTHERMAL CHAMBER TEST

Chang-Hui Lee,1 June Kee Min,2 Yoon Cheol Park,3 Namung Cho,1 and Sang Rok Oh1

1RIST, Pohang, Korea 2Pusan National University, Busan, Korea

3POSTECH, Pohang, Korea

ABSTRACT

In order to design the efficient system of the sodium-sulfur battery, the optimization of the thermal management system is essential because the cell is operating above 300 oC with the high-temperature condition. To figure out the thermal management of the system or battery module, the thermal modeling of the unit cell is a very basic and important step by observing the heat generation under the cyclic operation of the sodium-sulfur system. Basically, the reaction of the sodium-sulfur battery is quite complex during the charge and discharge of the cell. With the thermal system viewpoint, the reaction between sodium and sulfur is simplified to exothermic reaction when the cell is discharged and endothermic when it is charged. However, the thermal capacity of the cell needs to be clarified because the reaction of the cell is quite inhomogeneous along the cell. In this paper, the thermal properties of the cell such as thermal conductivity and thermal capacity were analyzed by the isothermal chamber experiment during the cyclic performance test in a certain range of operation. An experimental setup was developed that allows the investigation of the temperature response of the cell by using the calorimeter concepts. To get the accurate response, the thermal loss should be minimized throughout the whole experiment. Based on the research, the sodium-sulfur cell can be modeled by the heat source with various thermal capacities by the operation schedule.

Keywords: sodium-sulfur battery, thermal modeling, isothermal chamber test

INTRODUCTION

Nowadays, the sodium-sulfur batteries operated on high temperature are widely spread on load leveling applications based on their high energy density, high efficiency of charge/discharge, and long cycle life. In an earlier stage of development of sodium-sulfur batteries, most of the applications were diverged to the electric vehicle. However, since the 1980s, this battery has been a promising candidate for stationary energy storage. Moreover, this is one of the great successes that has been made for this application, especially in Japan and Europe [1].

Similar to all other battery systems, thermal management is very important to manage safe system operation. Moreover, high-temperature sodium-sulfur batteries are more important to predict their thermal response during their cyclic operation because of their temperature-sensitive characteristics in efficiency and the safety point of view. During the operation of sodium-sulfur batteries, the batteries

evolve the irreversible heat losses due to cell polarization, and the reversible losses due to its entropy change.

From the previous research [2, 3], most of the research was focused on the determination of the heat capacity and the heat generation rate of sodium-sulfur cells. In the cyclic operation of those cells, the adiabatic and isothermal procedure was applied to figure out their thermal characteristics. However, those cells are relatively low-capacity with small dimension compare to the recently developed higher-capacity cells, so the developed heat generation model has the fundamental limitation on their practical application for recently developed sodium-sulfur systems.

In the present study, the experimental approach to determine the heat generation of the recently developed sodium-sulfur battery has been suggested. The recently developed battery is designed to the

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higher capacity along with a bigger dimension. Figure 1 shows that the cell has higher length-to-diameter ratio in its geometrical characteristics; therefore, compared to the smaller cell, the longitudinal deviation must be considered when the cell is characterized in its thermal and electrical properties.

D = 81cm

H = 380cm

Fig. 1. Schematic and major dimension of the cell.

EXPERIMENTAL APPROACH

Cyclic Testing of The Cell

Figure 2 represents the experimental setup of charge/discharge cyclic operation of the sodium-sulfur cell. The purpose of the cyclic testing is to figure out the short-term electrical performance of the sodium-sulfur cell. During the cyclic testing, the cell temperature of the sodium and sulfur side was also recorded; the chamber is controlled by three-zone controllers.

For the cyclic testing, the cell is operated between 8 to 85% of its depth of discharge (DOD). The cell has the minimum resistance as 4.2 milliohms under 40 amperes current load.

Thermal Analysis

Generally, the heat generation rate Q can be calculated as the product of heat capacity and temperature change per unit time:

dtdTmcQ = (1)

If the measuring time and thus the temperature rise were kept low, dtdT will be constant and Q can be determined rather precisely. In this experiment, measurements on the test cell are made using the above procedure.

TCh

Insulation

Insulation

Vcell

TNa

TS

Fig. 2. Schematic of the cyclic testing of the cell.

Moreover, the thermodynamic equation for the heat generation Q in the electrochemical cell is:

−=

dTdETIQ η (2)

In the above equation, the first term represents the joule heating due to the electric resistance of the cell and the second term is an entropy term that represents the heat of reaction. The chemical reaction of the sodium-sulfur cell is exothermic for discharge and endothermic for the charge process. In the present study, the experimental correlation of the entropy generation by Knoedler [2, 3] has been compared with the experimental result.

RESULTS In Figure 3, the tested results with entropy

calculation were compared with the previous research of Knoedler and Sudworth [3, 4]. The experimental result is well matched considering the phase change at 60% DOD; however, the variable resistance by DOD change should be more discussed with more experimentation and proper modeling.

-0.0008

-0.0007

-0.0006

-0.0005

-0.0004

-0.0003

-0.0002

-0.0001

00 20 40 60 80 100 120

DOD (%)

dE/d

t (V)

Knoedler Sudworth

variable-R constant-R

Fig. 3. Comparison of the calculated entropy variation by DOD.

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REFERENCES [1] Z. Zhaoyin et al., “Research on sodium sulfur battery for energy storage,” Solid State Ionics 179, 2008, pp. 1697-1701.

[2] R. Knoedler, “Thermal properties of sodium-sulphur cells,” Journal of Applied Electrochemistry 14, 1984, pp. 39-46.

[3] R. Knoedler, “Calorimetric determination of the heat generation rate of sodium sulfur cells during discharge and charge,” Journal of Electrochemical Society 131 (4), 1984, pp. 845-850.

[4] J. Sudworth and A.R. Tiley, Sodium sulfur battery, Springer, 1985.

BIOGRAPHICAL NOTE Conference presenter: Dr. Lee is a senior researcher of RIST, South Korea. She is now involved in the assessment and analysis department considering reliability issues. She studied at the Korea Advanced Institute of Science and Technology

(KAIST) for her Ph.D., M.S., and B.S. degrees. Before she joined RIST, she worked for Samsung Electronics as a senior engineer in the home appliance division for more than five years. Her research interests mainly focus on product and technology development, considering the reliability concerns in the advanced energy storage system.

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PRELIMINARY FINDINGS OF NATIONAL RENEWABLE ENERGY LABORATORY’S

ELECTRIC VEHICLE LITHIUM-ION BATTERY SECONDARY-USE PROJECT

Jeremy Neubauer1 and Ahmad Pesaran1

1National Renewable Energy Laboratory, Golden, CO, USA

ABSTRACT

The high cost of lithium-ion batteries is a major impediment to both the increased market share of electric vehicles (EVs) and the proliferation of energy storage on the grid. The reuse of EV propulsion batteries in grid-connected second-use applications following the end of their automotive service life may have the potential to offset the high cost of these batteries for both markets. In this paper we estimate the financial viability of battery second-use strategies, considering the effects of competitive technology, the costs to repurpose automotive batteries, the value and size of grid-connected energy storage markets, and the deployment rates of EVs.

Keywords: energy storage, lithium-ion, EV, second use, battery salvage value

INTRODUCTION

Accelerated market penetration of electric vehicles (EVs) is presently restricted by the high cost of lithium-ion (Li-ion) batteries. Deployment of grid-connected energy storage, which could increase the reliability, efficiency, and cleanliness of the grid, is similarly inhibited by the cost of batteries. Research, development, and manufacturing are under way to improve the performance and reduce cost by lowering materials cost, enhancing process efficiencies, and increasing production volumes. Another possible path currently under consideration is to recover a fraction of the battery cost via reuse in other applications after it is retired from vehicular service, where it may still have sufficient performance to meet the requirements of other energy storage applications. By extracting additional services and revenue from the battery in a post-vehicle application, the total lifetime value of the battery is increased. Thusly, the overall cost of energy storage solutions for both the primary (automotive) and secondary (grid) customer can be decreased.

The U.S. Department of Energy’s Vehicle Technologies Program has funded the National Renewable Energy Laboratory (NREL) to answer these questions and investigate the second use of modern Li-ion EV batteries in grid-related applications. In this paper we estimate the financial viability of battery second-use strategies,

considering the effects of competitive technology, the costs to repurpose automotive batteries, the value and size of grid-connected energy storage markets, and the deployment rates of EVs.

ANALYSIS We take two approaches to estimating the

value of used EV batteries. First is a competitive technology approach, in which a maximum value for the used battery selling price is determined by requiring that used batteries be cost-competitive with equally capable new batteries. Subtracting the cost of repurposing yields the maximum achievable salvage value. Second is a generated revenue approach, in which maximum buying price estimates are determined by the value of applications anticipated to procure used batteries. To provide additional guidance on the viability of second-use strategies, the anticipated supply of used batteries is therefore compared to the financially motivated demand.

Competitive Technology Approach

Under the competitive supply approach, we assume (1) profitable and willing secondary use applications will be available at the time of the battery’s automotive service retirement, and (2) the principal competitor for second-use EV batteries in the selected second-use application is newly produced EV batteries. Under these assumptions,

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the premise that demand will exist for used batteries priced less than equally capable new batteries is valid. Thus the future selling price of a used EV battery will be proportional to the cost of an equally capable new battery, taking into consideration the health of the used battery and a used product discount factor (equal to the ratio of what a customer is willing to pay for a used product to what that same customer is willing to pay for an equally capable new product). Further details of this methodology are discussed in Reference 1, including means of estimating health factors and new battery costs. Under the assumptions therein, the estimated future selling price for used EV batteries produced today is generally less than $170 per kilowatt hour (kWh), primarily a result of an assumed steep 70% decline in new battery costs.

There are significant costs involved in the processes between retiring a battery from automotive service and selling it to a secondary market (collection, testing, repackaging, etc.). Cready et al. [2] estimated these costs at approximately $72/kWh. Subtracted from a maximum selling price of $170/kWh, this leaves a salvage value of less than $100/kWh to be paid to the automotive battery owner.

Generated Revenue Approach

Multiple studies on the value of utility-based energy storage applications have recently been released [3, 4]. In this paper, we leverage these works to first calculate the maximum revenue achievable on a dollars-per-kilowatt-hour basis for used EV batteries serving the utility applications reported on therein over a range of feasible discharge durations, rates, and depths of discharge. The results of our analyses on both sources suggest (Figure 1) that regulation, quality and reliability, and transportable transmission and distribution upgrade deferral are the most valuable applications.

Next we select specific discharge durations, rates, and depths of discharge for each of these four down-selected applications, aggregate the quality and reliability applications into one, and subtract the balance of systems costs using the most relevant data available from Reference 2. The resultant revenues and allowable battery costs are shown in Figure 2, showing that the balance of systems costs leave $217/kWh and $175/kWh to cover battery costs on average for area regulation and transportable transmission upgrade deferral, respectively. The average value for the power quality and reliability application has gone to

negative $73/kWh, suggesting that the balance of system costs outweigh the potential revenue before the costs of the battery are considered.

Fig. 1. Grid energy storage application revenue.

Fig. 2. Revenue and allowable battery cost for three down-selected grid energy storage applications.

Supply and Demand

It is additionally worth considering the relative supply and demand of used batteries. Accurately estimating available supply is challenging, as it depends upon the adoption rate of EVs, the type of EVs deployed, automotive battery life, etc. Our conservative forecast of used battery supply predicts approximately 2.5 gigawatt hours (GWh) could be deployed by 2030. Aggressive EV deployments and more optimistic assumptions about the number and state of batteries available for second use could increase this number to more than 30 GWh by that time.

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For comparison, our methods applied to the data in Reference 3 predict a total ten-year grid demand of 15.8 GWh for the down-selected applications. The fact that our allowable battery cost calculations show only subsets of the regulation and power quality and reliability markets to be cost-effective, and that there is growing competition from other technologies in each of these markets, means the actual achievable markets are likely smaller. On the other hand, the basis market projections in Reference 3 may need to be amplified to treat our principal period of interest (2020 to 2030). Thus there is too much uncertainty in our estimates to precisely contrast the supply of used batteries with the demand from the grid. However, it is observed that the supply has the potential to considerably overrun the demand, which would suppress battery salvage values if new, higher value markets are not identified.

CONCLUSIONS The analysis herein estimates a maximum

salvage value of ~$100/kWh and a maximum used battery sale price of ~$170/kWh, based upon the availability of competitive technology and the costs of repurposing. Having considered the value and market size of many grid-connected applications, as well as the balance of systems costs, it appears that area regulation, power quality and reliability, and transportable transmission and distribution upgrade deferral can supply a sufficient market at this price point under conservative EV deployment scenarios. Aggressive EV deployments could change things considerably by providing a surplus of used batteries, which would reduce the selling price and thus presumably open up additional markets. It is important to note, however, that there are many assumptions and uncertainties involved in making these estimates.

ACKNOWLEDGMENTS This study was supported by Dave Howell and

Brian Cunningham of the Energy Storage, Vehicle Technologies Program, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy. Special thanks to Mike Ferry and the CCSE second-use team for continued consultation and analysis of EV deployments.

REFERENCES [1] J. Neubauer et al., “The ability of battery second use strategies to impact plug-in electric vehicle prices and serve utility energy storage applications,” Journal of Power Sources, 2011, in print.

[2] Technical and Economic Feasibility of Applying Used EV Batteries in Stationary Applications, Sandia National Laboratories, Albuquerque, NM, 2002.

[3] Energy Storage for the Electricity Grid: Benefits and Market Potential Assessment Guide, Sandia National Laboratories, Albuquerque, NM, 2010.

[4] Electricity Energy Storage Technology Options: A White Paper Primer on Applications, Costs, and Benefits, Electric Power Research Institute, Palo Alto, CA, 2010. 1020676.

BIOGRAPHICAL NOTE Conference presenter: Dr. Jeremy Neubauer is a Senior Engineer with the National Renewable Energy Laboratory’s Center for Transportation Technologies and Systems. His primary responsibility lies in researching the reuse of retired automotive traction batteries to ultimately reduce the cost and accelerate the adoption of plug-in hybrid electric vehicles and electric vehicles. Before coming to NREL, Dr. Neubauer was Chief Engineer at ABSL Space Products, a leading manufacturer of lithium-ion batteries for the space industry. There he developed energy storage solutions for long-duration, high-reliability, and manned space missions. Dr. Neubauer has a B.S., M.S., and Ph.D. in Mechanical Engineering from Washington University in St. Louis.

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EFFECTS OF OPERATING PARAMETERS ON THE SINGLE-CELL PERFORMANCE OF THE VANADIUM REDOX FLOW BATTERY FOR ENERGY STORAGE

Chun-Hsing Wu, Hsin-Yi Liao, Kan-Lin Hsueh, and WenChen Chang

Green Energy and Environmental Research Laboratories (GEL), Industrial Technology Research Institute (ITRI), Chutung, Hsinchu, Taiwan

Keywords: energy storage, vanadium redox flow battery, electrode material characterization

The electrical power grid is in urgent need of a

new energy storage technology. This is because power generated from renewable energy, such as wind turbine and photovoltaic, is steadily increasing and the use of electric vehicles is growing rapidly. There are several available electricity storage technologies, namely hydro-pump, compressed air energy storage (CAES), and secondary batteries. The hydro-pump is the most mature, conventional storage for electrical energy; however, it is limited by geographical and environmental issues. CAES faces the same dilemmas as the hydro-pump. At present, several secondary batteries are attractive as the energy storage for photovoltaic and wind turbine system. They are lead-acid, lithium, metal hydride, sodium-sulfur, and redox flow batteries [1,2]. The redox flow battery is a good candidate for large-scale energy storage. Many test sites in the range from kW to MW were successfully demonstrated. The redox flow battery [3], especially the vanadium redox flow battery (VRB), is a promising energy storage technology because of its operation at ambient temperature, low cost, and long life cycle.

The current VRB system uses sulfuric acid at concentration around 2 M, and vanadium concentration of 1 to 3 M. The charge/discharge current density is around 40 to 80 mA cm-2. A new electrolyte with a less corrosive, high vanadium concentration and fast reaction rate is beneficial for a better VRB energy storage system. For less corrosive electrolyte, more choices of low-cost material can be used for safe operation and maintenance. For a fast reaction rate, the energy storage can be operated at high charging/discharging current. It also reduces the cell stack volume. Electrolyte with high vanadium concentration improves the energy density of the entire storage system.

The purpose of this work is to study various operating parameters on the performance of a single cell. Those parameters are electrode compression pressure, electrode surface pretreatment, electrode configuration, electrode catalyst, and electrolyte composition. The cell performance is evaluated by the cell voltage versus current (E-I) curve.

Electrolyte used in the single-cell study is 2.0 M VOSO4 + 2.0 M H2SO4 aqueous solution. This study used a conventional single cell for proton exchange membrane fuel cell testing. This cell has an electrode active area of 25 cm2 (5 cm × 5 cm) with serpentine flow channels. A hydraulic press was used for the electrode compression experiment. Nafion 117 (from du Pont) was used as the separator of single cell.

We investigated the effects of operating parameters on the single-cell performance (cell voltage versus current). In order to reduce the resistance to acceptable level, carbon felt needs a higher compression pressure than the carbon paper. The porous layer of the electrode adjacent to the membrane has better performance than that facing the flow channel. An electrode coated with catalyst improves cell performance. Electrolyte containing a high concentration of vanadyl ion is a significant improvement over electrolyte with low vanadyl ion (VO+2). However, concentrated electrolyte (4.0 M VOSO4) is not stable at a high current operating condition.

During this study, we designed and fabricated a new prototype single cell. Cell configuration is given in Figure 1. A short stack containing five cells was also built. Both the single cell and short stack will be tested and revised in the near future.

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Fig. 1. Configuration of a prototype single cell.

ACKNOWLEDGMENT

This work is carried out with financial support from the National Science Council (NSC) under contract number 97-2623-7-239-001-ET and 98-2623-E-239-001-ET. Experimental work was carried out by Ms. Hsin-Yi Liao as her M.S. Thesis, Department of Chemical Engineering, National United University. The authors wish to thank the technical assistant from Industrial Technology Research Institute/Green Energy and Environment Research Laboratories (ITRI/GEL). Part of this work will be published in Electrochemical Society Transaction 2011.

REFERENCES [1] K.C. Divya and J. Ostergaard, Battery energy storage technology for power systems—An overview, Electric Power Systems Research 79, 2009, pp. 511-520.

[2] M. Beaudin, H. Zareipour, A. Schellenberglabe, and W. Rosehart, Energy storage for mitigating the variability of renewable electricity sources: An updated review, Energy for Sustainable Development 14, 2010, pp. 302-314.

[3] C. P. de León, A. Fr´ıas-Ferrer, J. González-Garc´ıa, D.A. Szánto, and F.C. Walsh, Redox flow cells for energy conversion, J. Power Sources 160, 2006, pp. 716-732.

BIOGRAPHICAL NOTE Conference presenter: Dr. Chun-Hsin Wu is a researcher of the Green Energy and Environmental Lab (GEL) in the Industrial Technology Research Institute (ITRI). His graduate research was focused on the reaction kinetic

study on organic waste decomposition by a titanium dioxide photo-catalyst. After he obtained his Ph.D. in 2006, he joined the hydrogen and fuel cell research team of GEL and worked on catalytic reforming of natural gas, fabrication of electrodes, and development of metal bipolar plates. Since 2009, he was in charge as the project coordinator of large-scale energy storage, including metal-air batteries and redox flow batteries for grid-scale energy storage. Dr. Wu has 4 patents and 17 papers published in conferences and journals.

Session 8 – Emerging EES Technologies

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A NEW IRON/VANADIUM (FE/V) REDOX FLOW BATTERY

Liyu Li, Wei Wang, Zimin Nie, Baowei Chen, Feng Chen, Qingtao Luo, Soowhan Kim, and Gary Z Yang

Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA, USA

ABSTRACT

A novel redox flow battery using Fe2+/Fe3+ and V2+/V3+ redox couples in chloride supporting electrolyte and in chloric/sulfuric mixed-acid supporting electrolyte was investigated for potential stationary energy storage applications. The iron/vanadium (Fe/V) redox flow cell using mixed reactant solutions operated within a voltage window of 0.5~1.35 volts with a nearly 100% utilization ratio and demonstrated stable cycling over 100 cycles with energy efficiency > 80% and almost no capacity fading. Stable performance was achieved in the temperature range between 0 °C and 50 °C. Unlike the iron/chromium (Fe/Cr) redox flow battery that operates at an elevated temperature of 65 °C, the necessity of external heat management is eliminated. The improved electrochemical performance makes the Fe/V redox flow battery a promising option as a stationary energy storage device to enable renewable integration and stabilization of the electric grid.

Keywords: redox flow battery, hydrochloric acid, sulfuric acid, Fe/V, mixed acid, energy storage

INTRODUCTION

Redox flow batteries (RFBs) are electrochemical devices that store electrical energy in liquid electrolytes [1]. The energy conversion between chemical energy and electricity energy is carried out as liquid electrolytes flow through cell stacks. This advantage, along with their capability to safely store large quantities of electricity in a simple design and release it according to demands, makes it an ideal technology for the grid and micro-grid applications. Among the known redox flow batteries, the iron/chromium (Fe/Cr) and all-vanadium RFBs, or VRBs, are the two most widely developed. The Fe/Cr RFBs may be appealing for their potential low materials cost, but the low potential (-0.41 volts [V]) of the Cr2+/Cr 3+ redox couple can lead to hydrogen evolution during operation, complicating the system, raising the cost, and inviting safety concerns. VRBs demonstrate excellent electrochemical activity. However, the instability and high oxidation reactivity of the V5+ species in positive electrolyte require the use of high-cost Nafion membrane and limit operational temperatures to 10~40 oC [2]. This narrow operational temperature window and, in particular, the up limit (40 °C), often necessitate electrolyte temperature control in practical systems. Such heat management causes as much as 20% additional

energy loss and significantly increases the overall operating cost [3].

In our work, we proposed and investigated the electrochemical performance of a new RFB that employs a V2+/V 3+ solution anolyte and a Fe2+/Fe 3+

solution catholyte or a mixed solution as both the catholyte and anolyte. A standard voltage of 1.02 V can be obtained. The iron/vanadium (Fe/V) system was intended to make use of benefits from both Fe/Cr and all-vanadium systems while circumventing their intrinsic issues. Compared with the Cr2+/Cr3+ redox reaction, the V2+/V3+ pair possesses a much better electrochemical activity, which would free the system from using the expensive catalysts and the high-temperature management system. Moreover, the evolution of hydrogen (H2) gas during charging can be curtailed since the working potential of V2+/V3+ (- 0.25 V) is considerably higher than that of Cr2+/Cr3+ (- 0.41 V). On the positive side, the V4+/V5+ is replaced with the less oxidative and electrochemically reversible Fe2+/Fe3+ redox couple. Thus, the Fe/V system was expected to demonstrate an improved stability at elevated temperatures and also enable the system to use low-cost membranes other than Nafion. To demonstrate the capabilities of the proposed flow battery, the Fe/V redox couples in chloride-supporting electrolytes and in chloride/sulfuric acid

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mixed electrolytes were investigated for electrochemical properties, temperature stability, and performance. This paper reports the details of the work.

EXPERIMENTAL The electrolyte for the Fe/V redox flow battery

test was prepared by dissolving vanadyl sulfate (VOSO4), vanadium trichloride (VCl3), and iron chloride (FeCl2) in hydrogen chloride (HCl) and sulfuric acid (H2SO4). Cyclic voltammetry (CV) was carried out using Solartron 1287 potentiostat (Solartron Analytical, USA). A platinum (Pt) wire and silver/silver chloride (Ag/AgCl) electrode were used as the counter and reference electrode, respectively. A custom-made graphite felt (φ = 5.5 mm) electrode was used as the working electrode. The scan rate was 0.5 mV/s. The identical graphite felts without catalysts were used in both CV and flow cell testing.

The cell performance was measured under a constant current using an in-house-designed flow cell system that was connected with a potentiostat/ galvanostat (Arbin Institute, College Station, TX). The apparent area (i.e., the area in contact with the membrane) of the graphite felt was 10 cm2 (2 cm × 5 cm). Nafion membrane and Daramic hydrocarbon separator were used in the tests. An electrolyte volume of 50 milliliters (mL) and a flow rate of 20 mL/min were used during the tests. The flow cell was charged to 1.3 V and then discharged to 0.5 V at a current density of 50 mA/cm2. The composition of the electrolytes after cycling was determined by inductively coupled plasma/atomic emission spectroscopy (ICP/AES) after appropriate dilution.

During the stability tests, the samples were kept static without any agitation and monitored daily by the naked eye for any change of color indicating the oxidation of the membrane.

RESULTS AND DISCUSSION Figure 1(a) shows the CV results of 1.5Fe/

V-3.8HCl electrolyte. Two pairs of redox couples (V2+/V3+ and Fe2+/Fe3+) were observed in the sulfate-chloride mixed-acid solution, suggesting that the Fe3+/Fe2+ and V3+/V2+ redox couples have adequate reversibility to be used as the positive and negative electrolytes for the proposed RFB system.

0 20 40 60 80 1000

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Fig. 1. A cyclic voltammetry (CV) spectrum (a) on glassy carbon electrode in the 1.5Fe/V-3.8HCl electrolyte at 10 mV/s scan rate and the electrochemical performance of a Fe/V mixed acid redox flow cell with 1.5Fe/V-3.8HCl electrolyte in each half-cell and NR 212 as the membrane; (b) cell-voltage profile with respect to cell capacity during the 2nd and 100th cycles of the charge/discharge process; (c) cyclic coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) as a function of cycle number; (d) variation of specific volumetric capacity and discharge energy density with cycle number in a Fe/V mixed-acid redox flow cell using 1.5Fe/V-3.8HCl electrolyte in each half-cell with charge/discharge current density of 50 mA-cm−2.

The electrochemical cycling performance of

the RFB system based on the Fe2+/Fe3+ vs. V2+/V3+ redox couples was tested in the laboratory-made flow cell within the voltage window of 0.5~1.35 V at 50 mA-cm−2 current density with a NR212 membrane. As indicated by the CV scan results, no gas evolution issues were observed over a wide potential range of 1.8 V, which renders the Fe/V RFB with the sulfate-chloride mixed-acid supporting electrolyte considerable freedom with cell operational voltage control in maximizing the electrolyte utilization ratio while preventing the gassing problem. As shown in a typical plot of cell voltage profile with respect to the cell capacity (Figure 1(b)), the RFB cell performance corroborates the CV study, in which a state of charge in the range of 0~100% is demonstrated

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during the charge/discharge cycling, resulting in a utilization ratio close to 100%. Moreover, as shown in Figure 1(b), the voltage profile of the 100th cycle overlaps with that of the 2nd cycle, suggesting not only stable electrochemical cycling, but also a successful mitigation of the gassing issue over a long run (more than 30 days).

Figure 1(c) demonstrated the efficiencies of the Fe/V cell with the sulfate-chloride mixed-acid electrolyte up to 100 cycles, in which a CE of > 97% and a VE of ~85% were achieved, leading to an overall EE of ~82% at 50 mA-cm-2. The Fe/V cell also exhibited excellent capability retention as shown in Figure 1(d) with no obvious capacity loss throughout the 100 cycles. The discharge energy density representing the ultimate capability of the cell to deliver the useful energy is also plotted in Figure 1(d), in which close to 15 Wh-L-1 of specific volumetric energy density was obtained over 100 cycles of electrochemical cycling.

The cycling tests were then carried out at 25, 50, and 0 oC, with the flow battery cycled at each temperature over ~20 cycles (roughly 10 days). The electrolyte reservoirs were periodically examined, and no precipitation was found. At higher temperature (50 oC), a higher voltage efficiency of ~86% was obtained owing to the enhanced electrode reactions and reduced polarization at the elevated temperature. However, the cell performance was compromised with a lower CE of ~92% due to the increased crossover, leading to similar overall EE as for the cycling at 25 oC (~80%). At 0 oC, the system demonstrated a lower VE (~70%) and EE (~67%) caused by the more sluggish reaction and the increased electrolyte impedance at low temperature.

The cycling performance of the Fe/V cell at different temperatures affirms that the Fe/V flow battery with sulfate-chloride mixed-acid electrolyte can be operated in the temperature window of 0~50 oC. Given adequate insulation combined with generation of waste heat and subsequent system heating during operation, most areas around the world should thus be able to accommodate the Fe/V flow battery without the need for active heat management.

CONCLUSION A novel RFB system based on Fe2+/Fe 3+ vs.

V2+/V 3+ redox couples in sulfate-chloride mixed-acid electrolytes was successfully demonstrated in a laboratory-scale flow cell. With 1.5-M Fe and 1.5-M V in 1.5-M sulfate and 3.8-M total chloride solution, the redox flow cell achieved an EE of > 80% and no capacity fading over 100 cycles when employing NR212 as the membrane. The electrochemical cycling that was performed at different temperatures suggested that the Fe/V flow battery with sulfate-chloride mixed-acid electrolytes can be operated in the temperature window between 0 oC and 50 oC. The Fe/V flow battery with sulfate-chloride mixed-acid electrolyte using a polyethylene microporous separator as membrane delivers satisfactory cell efficiencies over 50 cycles, rendering great potential for developing a low-cost and long-life Fe/V RFB for large-scale energy storage.

ACKNOWLEDGMENTS The authors acknowledge the financial support

from the U.S. Department of Energy’s (DOE’s) Office of Electricity Delivery and Energy Reliability (OE). We are grateful for useful discussions with Dr. Imre Gyuk, the program manager of the Energy Storage and Power Electronics Program at DOE-OE. Pacific Northwest National Laboratory is a multi-program national laboratory operated for DOE by Battelle under Contract DE-AC05-76RL01830.

REFERENCES [1] Z. Yang, J. Zhang, M.C.W. Kintner-Meyer, X. Lu, D. Choi, J.P. Lemmon, and J. Liu, “Electrochemical Energy Storage for Green Grid,” Chemical Reviews 111, 2011, pp. 3577-3613.

[2] M. Skyllas-Kazacos, M.H. Chakrabarti, S.A. Hajimolana, F.S. Mjalli, and M. Saleem, “Progress in Flow Battery Research and Development,” Journal of The Electrochemical Society 158(8), 2011, pp. R55-R79.

[3] S. Eckroad, Vanadium redox flow batteries: An in-depth analysis, Tech. Rep. EPRI-1014836, Electric Power Research Institute, Palo Alto, CA, 2007.

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BIOGRAPHICAL NOTE Conference presenter: Dr. Liyu Li has broad experience in the fields of clean coal and biomass utilization, carbon dioxide capture, and redox flow batteries for grid-level electricity storage. He also has broad experience in developing inorganic absorbents,

hydrogen storage materials, heterogeneous catalysts, inorganic ion exchangers, and glass and ceramic nuclear waste forms. He has published 60

peer-reviewed scientific papers and has given more than 100 presentations at national and international scientific conferences in these areas. He also holds five U.S. patents, three foreign patents, and has eight U.S. patent applications on file. Dr. Li is a project manager and lead principal investigator at Pacific Northwest National Laboratory. At this position, he has both research management and technical supervisory responsibilities for the execution of governmental and industrial projects. Dr. Li joined Pacific Northwest National Laboratory in 1998.

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LIFETIME OF VANADIUM REDOX FLOW BATTERIES

Martha Schreiber and Martin Harrer

Cellstrom GmbH, IZNÖ-Süd Wr. Neudorf, Austria

ABSTRACT

Flow batteries in general and the vanadium redox flow battery in particular exhibit potentially long lifetimes. This is mostly because that most of the energy is stored outside the electrochemical cells and the all vanadium-containing electrolytes do not decay from cross-contamination. However, shift in vanadium valency due to membrane leakage, membrane aging, increase in internal resistance, and parasitic side reactions will influence the battery capacity and require service action to rebalance the electrolyte. But unlike in conventional secondary batteries, the full capacity can be restored repeatedly. Service lifetime depends very much on the application, and thus it is advised to rather use the term “application service life” since the same battery will achieve different service lifetimes in different applications. This presentation will deal with lifetime considerations from the technical, application, practical, and economic point of view.

Keywords: vanadium redox flow battery, battery lifetime, application service life, decentralized energy storage for wind and solar energy, off-grid and grid-connected energy storage systems

INTRODUCTION In conventional secondary battery systems,

performance data include C-rate, cycle life, and calendar life with strong dependency on state of charge (SOC) and temperature [1]. In flow batteries, C-rate has no significance since most of the electrolyte is stored outside the electrochemical cells. Therefore, there is a need to reconsider definitions that are very suited for secondary batteries but might not be useful for flow batteries. In general, lifetime is determined by technical performance and limitations due to battery chemistry, as well as structural features due to battery layout and design. This paper deals with service life considerations from the technical, application, practical, and economic point of view.

EXPERIMENTAL Service life predictions are difficult to derive

since accelerated lifetime test procedures often divert from conditions under real applications. On the other hand, it is very cost- and time-consuming to perform service life tests under real conditions. From the customer’s point of view, end of service life is defined when the battery does not meet the application requirement in terms of power and capacity. In reality, batteries are somewhat

oversized and applications may change over the years of use as well. The vanadium flow battery is best suited to accommodate for such changes.

For service life considerations, we have organized the battery in five major components: (1) the electrochemical cells and connectors, (2) the electrolytes contained in tanks, (3) pipes, pumps, and sensors, (4) power electronics, and (5) battery housing, including facility management such as air conditioning. In principle, each component can be replaced during maintenance, and economics will determine how long this may be sensible. In addition, there are technical limitations related to the battery chemistry that will have an impact on the lifetime of the electrochemical cells and the accessible capacity of the battery. While the electrochemical cells are subject to fail due to increase in internal resistance, the electrolyte capacity fade is due to an unbalanced vanadium concentration and shift in valency. Both failures can be corrected in situ by intermixing the electroytes and rebalancing. This is a fully reversible process and underlines the unique features of the vanadium flow battery.

In order to better understand the technical limitations of vanadium flow batteries, let us

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consider the open circuit voltage open current voltage (OCV) of the battery as a function of SOC at a given temperature (Figure 1).

Fig. 1. OCV versus SOC at 298 K of a 1.6 M volt sulfate system in 2 M sulfuric acid.

The OCV relationship from Figure 1 was obtained experimentally using the so-called OCV cell of the commercial battery. The OCV was measured under flowing conditions and the incremented charge was registered and converted into an SOC value in percent. The OCV values were corrected for temperature.

The OCV versus SOC relationship shows an s-shaped characteristic, thus revealing for every voltage difference a distinct value for the SOC. This is very valuable since information on SOC can be provided online. According to the electrode reactions during charging and discharging, four valencies of vanadium are present.

At the positive electrode:

VO2+ + 2H+ + e- = VO2+ + H2O

At the negative electrode:

V2+ = V3+ + e-

Overall reaction:

VO2+ + 2H+ + V2+ = VO2+ + H2O + V3+

In the negative electrolyte, V2+ and V3+ are present, while in the positive electrolyte V4+ and V5+ are present. During charging and discharging within one electrolyte the concentrations of vanadium in different valencies will vary; i.e., V2+ becomes dominant after the inflection point at 50% SOC, and in the negative electrolyte V5+ becomes dominant after the infection point. However, the

concentrations of V2+ and V5+, and V3+ and V4+ respectively, must be equal in order to obtain full capacity. In practical vanadium flow batteries the electrolytes become unbalanced during service life. The degree of unbalance depends strongly on the application. A shift to more V5+ is observed. Besides V5+ in solution, vanadium pentoxide (V2O5) can also precipitate in the positive tank and plumbing system. However, the amount is typically very small and negligible in terms of capacity loss. Despite that minor effect, (V2O5) can cause clogging of the electrochemical cells and cell failure. The reason for precipitation is increased temperature at high SOC. It is mostly the high SOC that limits the life of cells. Besides the V2O5 precipitation, oxidation of the graphite felt electrodes and bipolar sheet current collectors can occur and consume the carbon. Cell failure due to high internal resistance is the consequence. It would be best to avoid high oxidation states in the battery, i.e., when V5+ concentration exceeds 80%. The charging regime can be limited to that value of the expense of capacity. However, in unbalanced electrolytes, this value is difficult to handle.

Although a shift in valency will cause intermediate capacity loss, the vanadium is not lost and the full capacity can be recovered through rebalancing. The rebalancing process is done at the customer’s site and is another major advantage of the vanadium flow battery.

Service life of the electrochemical cells is limited by the internal resistance, which tends to increase over time and is also strongly dependent on the application. However, the cells can be replaced easily during maintenance and the power can be fully restored at a moderate cost. The electrolyte volume disposed with the electrochemical cells is marginal in cost and will be replaced with the new cells.

RESULTS AND DISCUSSION Service life cannot be separated from cost. As

described in the introduction, in principle all components of the battery could be replaced many times. But in many cases this would not be economically sensible. The critical number will thus be the total cost of storage in relation to the delivered energy – which of course is strongly application-dependent. Expected lifetimes for the components, pumps, and pipes and sensors can operate from 1 to 5 years. Electrolytes and tanks are expected to be used economically up to 20 years, as well as major parts of the battery housing. Power

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electronics will be subject to replacement by newer instruments with higher-efficiency models after 5 years, but could also be used up to 10 years.

The issue of internal resistance and electrolyte running out of balance are closely interrelated, where the membrane plays an important role with respect to unbalance and aging in the first place. Membranes with high selectivity are advantageous over membranes with higher conductivity and reduced selectivity. Once the electrolyte runs out of balance, the cells will suffer from high oxidation corrosion, increased self-discharge, and cell resistance. Therefore, the lifetime of cells is still the big question mark. Since cell failure can have many reasons, more field experience is needed to make better predictions. An open question on long-term performance is also the influence of minor impurities in the electrolytes.

Online data acquisition and analysis are important requisites to learn more about performance under real conditions from the past and help extrapolate into the near future. One interesting number for forecasting service life is the sum of times during which the battery was in a high SOC. How high the SOC can be tolerated remains to be seen. On the other hand, limiting the SOC may solve the problem, especially with highly selective membranes. The disadvantage is the higher cost due to lesser utilization of the electrolytes. However, the electrolytes can be rebalanced in situ and recovered from one system and used in the next.

CONCLUSIONS Service life of vanadium flow batteries is

strongly dependent on the application. The electrochemical cell is the most critical component. Although the electrolytes do run out of balance during service, they can be rebalanced during maintenance. All other components can be replaced under cost considerations. Service life can be extended as long as sensible.

The cost of energy generation and storage in units/kilowatt hours delivered will differ from application to application. It contains all costs from investment through maintenance and is a useful number for comparison with other resources such as grid or fossil fuels.

REFERENCES [1] D. Linden, “Secondary batteries service life,” Handbook of Batteries Second Edition, 1994, pp. 23.19-23.20.

BIOGRAPHICAL NOTE Conference presenter: Martha Schreiber is co-founder and managing director of Cellstrom. She has over 25 years of experience in battery research and development, all dedicated to the design and implementation of electrochemical

storage systems into mobile and stationary applications. She gained expertise in fundamental research at Stanford University and industrial experience at the Daimler Benz Company. Ms. Schreiber received a Diplom in Chemistry and a Ph.D. from the Technical University of Vienna, Austria, and a PhD from the Technical University, Delft, Netherlands.

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DEMONSTRATION OF ENERGY STORAGE USING A BREAKTHROUGH REDOX FLOW BATTERY TECHNOLOGY

Dr. Craig R. Horne

EnerVault Corporation, 1244 Reamwood Ave., Sunnyvale, CA, USA

Stationary energy storage applications requiring

multiple-hour duration present a large and growing market opportunity. Recent studies have found that energy storage systems with several hours of capacity have high potential for cost-effectiveness as a single system can serve several applications. These applications include utility transmission and distribution (T&D) upgrade deferral, variable renewable resource firming, demand response, and peak demand management. Furthermore, the highest-value location for an energy storage system is closest to the end user. Siting within high population densities elevates the safety requirements in both normal and abnormal circumstances. Additionally, the more distributed nature of energy storage systems requires that reliable operation can be achieved with minimal maintenance. These market realities necessitate that safety and reliability are equally important to cost-effectiveness for multiple-hour duration energy storage applications.

Redox flow batteries (RFBs) are a decades-old technology with intrinsic characteristics providing a high degree of safety: decoupled power and energy and aqueous electrolytes. The simple nature of the

reduction and oxidation reactions underlying an RFB’s electrochemical energy storage provides the foundation for long service life. However, cost-effectiveness of legacy RFB designs have been limited by the high cost of components and reactants while complex control requirements have hampered reliable operation. EnerVault is developing RFB energy storage systems based on its patented Engineered Cascade™ technology with a combination of safety, reliability, and cost-effectiveness that satisfies the requirements for multiple-hour duration energy storage applications.

This talk will describe the advantages of EnerVault’s novel Engineered Cascade™ RFB system architecture in terms of safety, reliability, and cost-effectiveness. We will also provide an update on the progress in developing systems based on our breakthrough technology. Lastly, the results of our NYSERDA PON1200 Project and the status of our Department of Energy American Recovery and Reinvestment (DOE ARRA) Storage Demonstration Project (in partnership with Ktech Corporation and matching funds from the California Energy Commission) will also be covered.

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Session 9 – EES Demonstrations

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COMMERCIALIZATION OF SILICON CARBIDE POWER MODULES FOR HIGH-PERFORMANCE ENERGY APPLICATIONS

J. Hornberger, B. McPherson, J. Bourne, R. Shaw, E. Cilio, W. Cilio, B. Reese, E. Heinrichs, T. McNutt, M. Schupbach, and A.B. Lostetter

Arkansas Power Electronics International, Inc. 535 W. Research Center Blvd., Fayetteville, AR, USA

ABSTRACT Over the past ten years, Arkansas Power Electronics International (APEI), Inc., has been developing advanced

next-generation power electronics capabilities through the design and implementation of silicon carbide (SiC)-based systems and platforms. SIC has the capability to reduce electrical energy waste by more than 90% and simultaneously reduce power electronics system size and weights by up to an order of magnitude, and it is poised to completely revolutionize the power electronics industry and reduce our dependence on foreign energy. The demands of modern high-performance power electronics systems are rapidly surpassing the power density, efficiency, and reliability limitations defined by the intrinsic properties of silicon-based semiconductors. The advantages of SiC are well known, including high temperature operation, high-voltage blocking capability, high-speed switching, and high-energy efficiency.

The high-performance power modules presented

within this discussion are new commercial products, employing the design techniques, advanced materials, and manufacturing processes developed by Arkansas Power Electronics International (APEI), Inc., to meet the demands of current and upcoming power electronic systems. This power module is rated to 1200 volts, is operational at currents greater than 150 amperes, can perform at temperatures in excess of 225 °C, and is designed to house various silicon carbide (SiC) devices, including metal-oxide-semiconductor field-effect transistors (MOSFETs), junction field-effect transistors (JFETs), or bipolar junction transistors (BJTs). The module is designed for high-performance commercial and industrial systems such as hybrid electric vehicles or renewable energy applications, implements a novel ultra-low parasitic packaging approach that enables high switching frequencies in excess of 100 kilohertz, and weighs in at just over 130 grams (offering ~5× mass reduction and ~3× size reduction in comparison with industry standard power brick packaging technology). It is configurable as either a half- or full-bridge converter.

The main goal for this module is to introduce to the market a commercial SiC module product (HT-2000 series) that can be used in the mentioned applications. A big credit to the success of this commercialization activity is the funding provided by

the U.S. Department of Energy Energy Storage Program through the Small Business of Innovative Research Phase I, II, and III programs. An image of the newly developed HT-2000 module is shown in Figure 1.

Fig. 1. HT-2000 series SiC power module with operating conditions of 1200 volts, >150 amperes, and 225 °C operations temperature.

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SECOND-GENERATION COMPRESSED AIR ENERGY STORAGE TECHNOLOGY MEETING RENEWABLE ENERGY/SMART GRID REQUIREMENTS

Dr. Michael Nakhamkin1 and Beat Achermann2 1P.E. and Chief Technology Officer, Energy Storage and Power, LLC,

520 US Route 22 East, Suite 205, Bridgewater, NJ, USA

2VP of Gas Storage, MAN Diesel Turbo, Hardstrasse 3198005, Zurich, Switzerland

ABSTRACT The Second-Generation Compressed Air Energy Storage (CAES2) technology is seriously considered by a

number of power generation utilities that are moving toward execution of the CAES2 projects. Dr. Michael Nakhamkin presented at the Mega-Session of the PowerGen 2010 the fundamentals of the Compressed Air Energy Storage Technology from the first 110-megawatt (MW) CAES project in Alabama to the second generation of CAES2 co-sponsored by Department of Energy (DOE) for two upcoming CAES projects.

This paper will present newly developed CAES2 features to meet specific smart grid and renewable energy requirements as well as limitations provided by the underground storage characteristics.

The presentation will include the approximate 200-MW, 350-MW, and 450-MW CAES2 plants with demonstration of flexibilities to meet specific smart grid and renewable energy requirements and specific characteristics for underground storage limitations including:

• Heat and mass balances indicating the heat rates (3700 to 3900 Btu/kWh) and energy ratios (0670.75);

• Synchronous reserves with delivery of approximately 60% of the total capacity within 2 minutes from the cold-startup;

• Regulation opportunities to practically instantly change power generation capacities between 40% and 100%;

• Part-load operations with very high and stable efficiency; and

• Capital and operational costs.

The paper will also address the newly developed concepts for:

• Small capacities of CAES2 plant of approximately 5 to 15 MW with above ground storage with new developments to enhance the small capacity CAES plants economics; and

• New developments related to adiabatic CAES plants.

The information will be very important for the

power generation community.

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SYSTEMS INTEGRATION STRATEGIES FOR THE 10-kWh REDFLOW ZINC BROMINE BATTERY MODULE

Steve Hickey, Head of Battery Testing

RedFlow Limited, Brisbane, Queensland

INTRODUCTION Modern energy storage systems are most credibly

demonstrated in field applications.

Over the past three years, RedFlow has deployed its commercial flow battery, the 10-kWh zinc bromine module (ZBM), in progressively more sophisticated and reliable packaged energy storage systems. In doing so, RedFlow has embedded its ZBM in systems constructed with contemporary (commercial) power electronics.

These devices (commercial inverters and rectifiers) are designed to support Battery Management Systems (BMSs) for lead-acid (LA) battery characteristics. RedFlow’s system integration engineers have progressively adopted these products and, with some assistance from the relevant manufacturers, have developed strong and reliable packaged energy storage systems based on ZBMs.

This paper reviews the evolution of this product strategy through four products deployed by RedFlow in both grid-connected and off-grid applications.

The reference design is a system based on a 48-volt LA battery bank grid tied with an inverter/rectifier. All of the systems presented incorporate the SMA brand Sunny Backup or Sunny Island devices (the latter for off-grid) and in sequence were:

(1) A grid-tied system employing hybrid ZBM-LA storage and a set of algorithms to control power flow (20 units);

(2) An off-grid solar photovoltaic (PV)-based system also with hybrid storage but using maximum power point trackers (10 units);

(3) A larger (grid-tied) solar PV-based system three-phase hybrid design again with maximum power point tracking (MPPT) power control (1 unit); and

(4) Pure ZBM-based systems with algorithmic power control (60 units).

RedFlow's product development investment is ongoing. Our new highly efficient DC/DC converter is anticipated as the next phase of the evolution, resulting in a BMS that will make the flow battery into a standardized plug-and-play product compatible with many existing power systems designed with LA batteries.

BIOGRAPHICAL NOTE Steven Hickey received a Bachelor of Electrical Engineering at University of Queensland in 1982. After a brief stint as UQ Energy Management Engineer, he moved to the Julius Kruttschnitt Mineral Research Centre (JKMRC) for the mining research program, working on seismic and blast vibration instrumentation. This experience led in 1988 to his founding (with colleagues) Blastronics Pty. Ltd., which gained an international reputation as a leading consulting and instrumentation business.

Joining RedFlow in mid-2008 as Test Engineer, he is amongst the most senior employees. Recently, he has been responsible for systems design, and for mentoring junior engineers. He currently manages the company’s long-term ZBM test program.

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MANAGING THE STATE OF CHARGE OF ENERGY STORAGE

SYSTEMS USED FOR FREQUENCY REGULATION

Matthew Lazarewicz

Beacon Power Corp., Tyngsboro, MA, USA

ABSTRACT

This paper summarizes approaches used by Independent System Operators (ISOs) and Regional Transmission Organizations (RTOs) in managing the state of charge of energy storage systems used for frequency regulation (an ancillary service supporting power balance on the grid). Two different approaches have evolved and been tested and will be summarized. This paper uses commercial field data to show the benefits of fast performance, to highlight lessons learned, and to suggest how to best use the assets in the future.

Keywords: frequency regulation, flywheel, policy, state of charge management

INTRODUCTION

Frequency regulation on a power grid is an ancillary service used to balance power generated and load to maintain a target frequency, usually 60 or 50 Hz. It is also used to manage unscheduled tie flows for a given balancing area to net at zero within a 15-minute time period. Deviation from this balance is called Area Control Error (ACE). Historically, frequency regulation was provided by generators whose outputs were regulated to follow the system operator regulation signal using an automatic generator control (AGC). Typically, the generator was required to fully respond to the signal in 5 minutes. This response time is significantly slower than the few seconds a load can change with the throw of a switch. Existing market rules recognized generation as the only asset that could provide this ancillary service. In 2007, the Federal Energy Regulatory Commission (FERC) issued Order No. 890 mandating market rule changes that would open competition to other technologies. Energy storage using a flywheel-based system was proposed to provide frequency regulation as a low-cost alternative.

Grid operators considering storage alternatives for frequency regulation expressed concern that if the imbalance lasted too long, it might be possible to either fill or empty all the energy from the storage device, negatively affecting performance. There was also the question of whether storage is a generator or a load. The classification made a big difference

insofar as who could own and operate such a system in a deregulated environment. It was recognized that energy storage at times behaved like a generator, and at others like a load, but neither conventional generator control nor demand response were adequate to manage the storage device. It became apparent that storage resources required their own control methodology. See Figure 1. The approach taken by the Independent System Operators (ISOs) and Regional Transmission Organizations (RTOs) was that storage should be treated in one of two ways:

(1) Manage the state of charge so as to treat the device as a generator when nearly fully charged, and as a load when nearly empty.

(2) Devise a way to control the storage system with an energy-neutral control signal (zero bias), so that the charge of the system never gets empty or full.

Fig. 1. Separate asset class for energy storage.

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In responding to FERC Order No. 890, the ISOs developed creative state-of-charge methodologies using one of those two approaches to ensure the storage.

Speed Matters

It was recognized that the effectiveness of ACE correction is actually a function of both the amount of megawatts (MW) of imbalance and the time it takes to correct the imbalance. See Figure 2. The amount of balancing energy delivered by a slow-ramping generator, shown on the right, is limited by the ramp rate, but can continue indefinitely. The faster the ramp rate, the more balancing energy can be delivered. Independent System Operators-New England (ISO-NE) recognized this and has used the approach of dispatching fast assets first, with the result that they require a lower percentage of average load than other ISOs. Energy storage, on the other hand, has the ability to respond and even reverse direction much quicker and therefore deliver more balancing energy, but can be limited in energy. In addition, slow-ramping resources cannot switch directions quickly. They sometimes provide regulation in a direction that is counterproductive to the needs of the grid and, as a result, actually add to the ACE, requiring another resource to be dispatched to counteract it.

Fig. 2. Fast ramp capability is more effective.

The Frequency Regulation Pilot Program in

ISO-NE shows a comparison of the two characteristics plus the effect of dispatching the faster resource first. See Figure 3. The energy delivered by the storage device is the area under the signal curve. (The signal and storage response are on top of each other.) The ramped curve represents a response of a generator with a 5-minute response. Notice the significant difference in delivered energy (area under the curve) between the storage and generator assets.

Fig. 3. Effectiveness comparison of storage and conventional generation-based regulation.

ISO/RTO RESPONSE SUMMARY

The paper will describe in detail how the RTOs approached storage-based systems. Data from the 20-MW plant in Stephentown, NY, will be used to illustrate New York Independent System Operator (NYISO) performance. The next plant to be built will be in Hazle Township, PA, within PJM control. Status of that plant will be reported.

NYISO/MISO

Both NYISO and Midwest Independent System Operator (MISO) implemented a four-step process to accept storage [1]:

(1) Create a new storage asset category called Limited Energy Storage Resources (LESR) and allowing resources to supply regulation only with no requirement to supply energy;

(2) Develop a method to manage the state of charge in the storage device utilizing a 5-minute energy market;

(3) Modify their dispatch to take advantage of fast response by treating storage as a “first responder,” which reduced reliance on slower-responding units; and

(4) Devise a new net energy settlement for LESRs (Hourly settlement = (energy in – energy out) x LBMP).

FERC approved both tariffs in 2009.

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ISO-NE

ISO-NE recognized the AGC signal was not neutral and caused the storage device to either fill or drain empty. They launched a pilot program to develop methodology to address this issue. Beacon Power created an algorithm that modifies the base point and treats the asset like a generator when near full, and like a load when near empty. Process forces state of charge to maintain mid-point energy.

PJM

PJM took a two-signal approach: a conventional AGC signal for generators and an energy-neutral fast ramping signal for storage. This approach was used with an AES energy storage demonstration in PJM. PJM is awaiting FERC approval of their tariff.

CAISO

California Independent System Operator (CAISO) tested a split-signal approach (see Figure 4) using Beacon flywheels in 2006 where the regulation signal was divided by using a rolling 5 to 10-min average to control generators and reduce the number of reversals and ramp rate requirements. The rest of the imbalance was sent to the storage device. CAISO has recently submitted their tariff to FERC and is awaiting approval.

Fig. 4. CAISO approach to signal split.

REFERENCES [1] R. Mukerji, R. Pike, and J. Hickey, Integration of advanced storage technologies in the New York wholesale electricity market, CIGRE document C5_210_2010.

BIOGRAPHICAL NOTE Mr. Lazarewicz has been with Beacon Power Corp. for 12 years, where he serves as Vice President and Chief Technical Officer. Before joining Beacon Power, Mr. Lazarewicz worked for 25 years for General Electric in

various engineering and managerial capacities in Power Systems and Aircraft Engines. He is a Mechanical Engineer and holds B.S., M.S., and MBA degrees from the Massachusetts Institute of Technology. He is also a Registered Professional Engineer in Massachusetts. He serves as Vice-Chairman of the Electricity Storage Association, Chairman of the Energy Storage Working Group of the Distributed Generation and Energy Storage Sub-Committee, and a member the Institute of Electrical and Electronics Engineers (IEEE) Power Engineering Society, American Society of Mechanical Engineers (ASME), International Council on Large Electric Systems (CIGRE), and the National Electrical Manufacturers Association’s (NEMA’s) Energy Storage Council.

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Session 10 – EES Special Applications

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WHY AREN’T WE BUILDING NEW GRID-SCALE ENERGY STORAGE PROJECTS? THE CASE FOR PUMPED STORAE

Michael Manwaring, Rick Miller, and Kevin Snyder, HDR

While many forms of energy storage are in various stages of development and commercial deployment, pumped storage hydropower is the most widely used energy storage application, with over 127,000 megawatts (MW) installed worldwide, representing over 99% of the existing installed electric energy storage capacity. It is observed from the existing 22,000 MW of U.S.-based pumped storage that the real value of this technology has gone from balancing peak/off-peak demand periods to enabling the overall power system to operate more reliably and efficiently. Worldwide, wind power has increased from approximately 15,400 MW in 2000 to over 145,000 MW in 2010, and with numerous societal pressures and policies promoting the use of green energy, the penetration of wind resources is only expected to increase. The result of this growth in a naturally variable energy source will be the need for rapidly responding, flexible generation sources combined with fast and ultra-fast response or energy storage to instantaneously balance electrical generation and load.

A relatively new design for pumped storage projects is to develop both the upper and lower reservoir off of a main stem river system, thereby eliminating any aquatic and fishery impacts of the project. These projects are typically termed “closed loop” pumped storage, because after the initial filling of the reservoirs, the only water requirement to operate the projects is the occasional makeup water required to offset evaporation or seepage losses. These designs have greatly reduced potential environmental impacts of pumped storage projects by avoiding controversies related to endangered or protected and other aquatic species.

New variable-speed pumped turbine projects (also called adjustable speed) recently constructed in Japan and Europe have demonstrated yet another degree of new operating capabilities, flexibility of operation, and improved efficiency. This technological advancement may provide the greatest

ancillary benefit to grid operators in the United States, as current pumped storage plants do not provide regulation in the pumping mode because the pumping power is fixed (i.e., a project must pump in “blocks” of power). However, variable-speed pumped storage units are able to modulate input pumping power and provide significant quantities of frequency regulation, including both incremental and decremental reserves.

Considering these advantages, the question of why pumped storage or grid-scale energy storage projects are not being developed at a pace similar to renewable generation is compelling. As an answer, legislative, regulatory, and financial obstacles exist that are restricting such development of any grid-scale energy storage project, including pumped storage hydropower. The inability to easily and confidently quantify and value the ancillary benefits of pumped storage makes long-term revenue contracts extremely difficult, combined with challenges in obtaining approvals from regional transmission authorities, and the current regulatory environment has stymied many potential projects.

This paper will discuss recent regulatory and technological developments for pumped storage hydropower and the concepts presented in the National Hydropower Association’s August 22, 2011, filing to the Federal Energy Regulatory Commission (FERC) in response to their Notice of Intent for ancillary services for energy storage technologies. Several actions were recommended in the FERC filing that could increase the potential for development for grid-scale energy storage technologies like pumped storage by providing opportunities for long-term revenue streams. These include adapting the current Avista restriction to allow energy storage technologies to participate in the ancillary services market more robustly and developing a new energy storage asset class, similar to the gas storage model already adopted by the FERC.

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ENERGY STORAGE—A CHEAPER, FASTER, AND CLEANER ALTERNATIVE TO CONVENTIONAL FREQUENCY REGULATION

Janice Lin and Giovanni Damato

StrateGen Consulting, LLC, 2150 Allston Way, Suite 210, Berkeley, CA, USA

StrateGen Consulting completed the white paper

Energy Storage—A Cheaper, Faster, and Cleaner Alternative to Conventional Frequency Regulation for the California Energy Storage Alliance (CESA) to conduct a side-by-side comparison of a natural-gas-fired combined cycle combustion turbine (CCGT) to a flywheel energy storage system for frequency regulation in California. The comparison includes performance, financial analysis, and emissions. Key findings from this analysis include the following:

• Energy storage can be 2.5 times more effective at performing frequency regulation than a conventional CCGT.

• Energy storage is a cleaner alternative to conventional plants with respect to air quality impacts.

• Energy storage is a more cost-effective alternative to conventional power plants performing frequency regulation.

The presentation of these findings will include a

thorough review of the ways in which conventional ancillary services are supplied, the utilization of energy storage for the operational use of frequency regulation, as well as a detailed financial comparison of the gas-fired combustion turbine to a flywheel from the perspective of a merchant plant owner. In addition to the financial analysis, the presentation will illustrate the air quality benefits associated with substituting conventional frequency regulation with energy storage. It will also explore why and how energy storage performs regulation 2.5 times better than conventional plants. Finally, the presentation will lay out the key market and regulatory challenges involved with utilizing energy storage to provide frequency regulation and recommend a clear pathway to overcome these hurdles.

Figure 1 gives a general overview of the comparison’s assumptions and results. Figure 2 illustrates the effects of a flywheel’s performance factor on Internal Rate of Return (IRR) and emissions.

The full white paper and the associated model can be downloaded from CESA’s website: http://www.storagealliance.org/work-whitepapers.html.

Fig. 1. Case study assumptions and results.

Fig. 2. Flywheel performance factor effects on IRR and emissions.

http://www.storagealliance.org/work-whitepapers.html

http://www.storagealliance.org/work-whitepapers.html

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BIOGRAPHICAL NOTE Conference presenter: Giovanni Damato has led StrateGen’s Value Proposition Practice in distributed energy storage since 2005. Storage technology providers, global solar integrators, leading real estate developers, and public utility

commissions have sought out his expertise to make critical strategic decisions about distributed storage markets, including the integration of storage with renewable energy resources. He is currently advising suppliers and developers as well as clean energy end users to develop the value proposition and strategic implications of photovoltaic, solar thermal, and advanced energy storage systems for a wide range of key stakeholders.

Mr. Damato brings practical and analytical skills to StrateGen from the construction industry. Before joining StrateGen, he founded a custom homebuilding business and is a licensed General Contractor in the State of California. Incorporating green building into his homebuilding business ultimately led Mr. Damato to the clean energy space and StrateGen. He has also worked for Granite Construction, a leading U.S. heavy civil transportation contractor, as a Field Engineer on the Las Vegas Monorail Project, where he was responsible for day-to-day construction activities and jobsite/public safety.

Mr. Damato holds an MBA from the Stanford Graduate School of Business and a B.S. in Civil Engineering from California Polytechnic State University, San Luis Obispo. He enjoys adventure traveling—including Mount Everest, Aconcagua, and Kilimanjaro.

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ULTRACAPACITOR TECHNOLOGY FOR UTILITY APPLICATIONS

Andrew Burke

University of California-Davis, Institute of Transportation Studies, Davis, CA, USA

There are a number of utility applications

requiring high-power energy storage devices like lithium batteries and ultracapacitors. In this paper, recent test data for the performance of new commercially available devices from Ioxus and Nesscap are presented along with data for advanced prototype devices from Yunasko (Ukraine) and Skeleton Technologies (Estonia). All these devices utilize carbon/carbon electrodes and an organic electrolyte with rated voltages of 2.7 to 2.85 volts (V). The capacitances of the devices are 350 to 3000 F. The devices were tested at high currents (up to 400 amperes) and high powers (up to 2200 watts/kilogram [W/kg]) in both the constant and pulse power modes. The usable energy densities are 4 to 6 Wh/kg and the 95% efficient power densities are 1000 to 2700 W/kg. All these devices are suitable for high-power, DC utility applications.

Some utility applications require pulsing at 60 cycle AC. Some of the new devices tested have RC time constants significantly less than 1 second and can be pulsed with times in the millisecond (msec) range. Test data are presented for 5 msec pulses and cycling periods of 15 msec with no loss of capacitance and very low resistance. This indicates the device could be used to provide load leveling for 60 cycle AC loads.

Data for the Skeleton Technology 350 F device are shown in Table 1.

Table 1. Constant Power Discharge Data. Power

W W/kg

(1) Time sec Wh Wh/kg Wh/l

17 247 59.1 .284 4.06 7.67 24 339 43.5 .286 4.09 7.73 41 590 23.9 .274 3.92 7.39 60 858 16.0 .267 3.81 7.2 80 1142 11.7 .26 3.71 7.01 109 1554 8.5 .257 3.67 6.94 155 2214 4.9 .211 3.01 5.69

Discharge 2.85 V to 1.42 V (1) All characteristics based on packaged weight and volume.

Pulse Power Calculation at 95% Efficiency

P=9/16 × (1- eff) V0 2 /R = 9/16 × (.05) (2.852 /.0012

= 190W

(W/kg)packaged = 170/.070 = 2714

Matched impedance power V2 /4R = (2.85)2/ (4*.0012) = 1692, 24 kW/kg packaged

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199

ULTRABATTERYTM STORAGE TECHNOLOGY AND ADVANCED ALGORITHMS AT THE MEGAWATT SCALE

Dr. Peter Coppin1 and Mr. John Wood2

1Storage for Renewables, CSIRO Energy Transformed Flagship, Canberra, ACT, Australia 2CEO Ecoult, Sydney NSW, Australia

UltraBattery technology, a combination of

conventional valve-regulated lead-acid (VRLA) and super-capacitor technology, has reached system implementation at the megawatt (MW) scale. East Penn Manufacturing Co. has implemented UltraBattery into its stationary battery production capability supporting high-volume manufacturing capability. This has enabled the design and implementation of systems at the MW/megawatt hour (MWhr) scale for a variety of applications. Systems have or are being installed for wind and solar energy production smoothing, renewable energy peak shaving, and regulation services.

Ecoult, working with CSIRO in Australia, has progressed technology characterization and application together through laboratory qualification and simulations through to MW scale at the Hampton Wind Farm. As the work has progressed there have been significant understandings developed. An approach has been followed of preparing the technology for application-independent flexibility both in a system design sense and in an operational sense. This approach has now resulted in a strong storage solution platform approach.

Having refined the platform base we now have the ability to bring real innovation to energy storage. There is a considerable amount of effort being put into developing more intelligent ways of operating the storage systems and developing algorithms that are adaptive to the prevailing inputs (e.g., service demands or renewable energy inputs), while minimizing degradation of the storage asset.

Mr. John Wood, CEO of Ecoult, will discuss the status of the technology and platform development and Dr. Peter Coppin, CSIRO’s Head of Storage for Renewables research, will introduce the intelligent algorithm work currently being progressed on top of the platform.

The wind-smoothing systems at Hampton wind farm in New South Wales, Australia, has progressed from laboratory trials to a MW-scale commercial system from Ecoult Ltd. Initial results with the first stage of the system show that with a simple proportional-integral, fixed-parameter algorithm, significant reductions in rates of change of power output (ramp rates) can be achieved. Figure 1 shows results from one day with a variety of wind conditions. The lower traces show the raw turbine input and the smoothed output when combined with the storage system. The upper traces show the reduction in 5-minute ramp rate, which averages a factor of 7. The 1-minute ramp-rate reduction achieved by the system is a factor of 10.

-30

-20

-10

0

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0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12 21:36 0:00

Ram

p ra

te k

W p

er 5

min

kW

time (hh:mm)

5 min Ramp rate Chart 2010-12-26_to_2010-12-27

storage.powerIn storage.powerOut storage.targetPowerOut5 min Ramp rate In 5 min ramp rate out

Fig. 1. Smoothing of wind output and ramp rate reduction with fixed-parameter controller algorithm.

A more advanced algorithm system is being developed. The system, shown in Figure 2, works as an adaptive scheme that allows the smoothing parameters to be continuously changed. An offline optimizing scheme is used to design the functions used in real time. The optimization takes into account a number of objectives (goals) and costs while being aware of system electrical and physical constraints. The system can be re-optimized for each installation. Initial trials show a significant improvement is possible using this approach.

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UltraBattery has proven to have an extraordinary endurance and longevity performance when used for applications where power is cycled in a partial state of charge band. The UltraBatteries used at Hampton (manufactured by East Penn Manufacturing in the United States) have exhibited this outperformance where the state of charge range is wide (40 to 60% +). The objective is to deliver maximum impact on signal quality for minimum cost by combining the UltraBattery cycle longevity (which reduces the cost of each MWh of storage used) with intelligent algorithms that reduce the ratio of storage MWh required for the impact.

OfflineMachine Learning

Fitting Engine(compute intensive)

ControllerAlgorithm

Real TimeMachine LearningExecution Engine

(fast)

Source and System State•Day, time of day•Recent history of input power signal•(Forecast input signal)•Rate of change•Power variance•SOC•Storage System power setting

History

Objectives: Ramp rate, Max allowable/Tolerance for peaks

Costs: Battery Work, Integrated Cycles, Price of storage and power

Electrical limits: Max power, max rate of change, SOC limits, Delays

Physical constraints: eg.No charging of AC mains, No exceeding max output of source

Variable PI coefficients

Real Time

EquationParameters

Fig. 2. Schematic of wind-smoothing algorithm development system.

BIOGRAPHICAL NOTES

Conference presenter: Peter Coppin received his B.Sc. (Hons) degree in 1974 and his Ph.D. degree in micro-meteorology from Flinders University of South Australia in 1978. After completing a post-doctoral fellowship at the University of Hannover,

Germany from 1978 to 1980 in wind energy, he was appointed as a research scientist at CSIRO in 1980.

Mr. Coppin was Director of the CSIRO Wind Energy Research Unit until 2009 and is currently Leader of the Storage for Renewables Stream at the Energy Transformed Flagship. His research interests include boundary-layer meteorology, wind energy, and renewable energy storage.

He was Director of the CSIRO Wind Energy Research Unit until 2009 and is currently Leader of the Storage for Renewables Stream at the Energy Transformed Flagship. His research interests include boundary-layer meteorology, wind energy and renewable energy storage.

John Wood, Mr. Wood is the Chief Operating Officer of Ecoult. He John joined the energy storage community in 2008 having previously launched technologies globally in Security,

Identity, Payment Technology, and Telecom-munications.

As a technology CEO for more than 20 years Mr. Wood has had the good fortune to have worked with excellent individuals and led excellent teams that have created businesses and numerous successful products and solutions from the ground up that are used and trusted by many of the world's largest enterprises and governments, either directly or under license by many of the largest global technology enterprises.

Mr. Wood is now leading the Ecoult effort to commercialize UltraBattery storage solutions.

Session 11 – Compressed Air Energy Storage (CAES)

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203

NEW YORK STATE ELECTRIC AND GAS AMERICAN RECOVERY AND REINVESTMENT ACT ADVANCED COMPRESSED AIR ENERGY

STORAGE DEMONSTRATION PLANT – 2011 STATUS

James Rettberg1 and Dr. Robert B. Schainker2 1New York State Electric & Gas, Binghamton, NY, USA 2Electric Power Research Institute, Palo Alto, CA, USA

This paper will present the current status of the New York State Electric & Gas (NYSEG) Advanced Compressed Air Energy Storage (CAES) Demonstration Plant Project, which is co-funded by the U.S. Department of Energy’s (DOE’s) Smart Grid Program and is classified as a DOE American Recovery and Reinvestment Act (ARRA) Regional Demonstration project. NYSEG will work with selected consultants, contractors and vendors to complete the installation of an advanced CAES plant sited in Reading, New York, at the southern end of Seneca Lake, near Watkins Glen, in New York State’s Finger Lakes region. The plant is to have a capacity in the range of 130 megawatts (MW) to 210 MW with up to 10 hours of storage – which is sufficient to provide a wide range of operational benefits on the NYSEG power system. As part of the project, a period of two years of monitoring will be conducted that is independent of any existing manufacturer/vendor or utility system monitoring. The CAES plant monitoring will be configured to quantify both plant operational and transmission grid system benefits. A secure data acquisition system will collect, analyze, and disseminate data regarding system operational performance from the local plant point of view and from the New York Independent System Operator (NYISO) point of view.

The NYSEG advanced CAES plant will use electricity to compress air into a solution mined salt cavern air storage system. When electricity is needed, the high-pressure air is withdrawn, heated via combustion, and run through an expansion turbine to drive an electric generator. Compared to a combustion turbine, such plants burn about one-third the premium fuel and produce about one-third the carbon dioxide and other pollutants per kilowatt hour of plant output.

The current status of the NYSEG CAES project presented in this paper will include an overview of the project’s management plan, technical architecture and

engineering services, and economic energy market analysis services.

BIOGRAPHICAL NOTES James Rettberg is a Project Manager employed by New York State Electronic Gas, a subsidiary of Iberdrola USA. His experience spans over 30 years in management of fossil generating units and in managing major technical projects. Mr. Rettberg holds a B.S. degree in

mechanical engineering from Lehigh University, and an MBA degree from Syracuse University. Mr. Rettberg is a Registered Professional Engineer in New York and Pennsylvania.

Conference presenter: Dr. Robert Schainker is Senior Technical Executive in the Electric Power Research Institute Power Delivery and Utilization Sector. His research activities cover energy storage, generation, and transmission technologies with special focus on compressed air energy storage,

battery energy storage, strategic planning, electric grid dynamic stability, transmission substations, high-voltage power flow controllers, transformers, and power quality. Dr. Schainker has given expert testimony to the U.S. Congress, the U.S. Federal Energy Regulatory Commission, and the California Public Utility Commission on strategic planning and a wide variety of electric utility technologies to improve the efficiency and “smartness” of the U.S. grid. Dr. Schainker holds three patents and has written chapters in two encyclopedias on electric grid and energy storage technologies. Dr. Schainker holds a B.S. degree in mechanical engineering, an M.S. degree in electrical engineering, and a Ph.D. in applied mathematics, all from Washington University in St. Louis, Missouri.

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205

IOWA STORED ENERGY PARK “LESSONS FROM IOWA”

Kent Holst

Traer, IA

The Iowa Stored Energy Park (ISEP)

organization has been developing a Compressed Air Energy Storage (CAES) site for several years. Extensive seismic surveys, several economic feasibility studies, three exploratory wells, and the physical and chemical analysis of core samples from the exploratory wells have all been undertaken to complete our due diligence for this project.

This investigative work has been funded by a combination of entities, including 57 municipal utilities in Iowa, Minnesota, North and South Dakota, the State of Iowa Office of Energy Independence, and the Energy Storage Program of the U.S. Department of Energy. Over $8.6 million has been spent to date. Work has been carried out by The Hydrodynamics Group, LLC; Bay Geophysical; Sandia National Laboratories (SNL) in Albuquerque, New Mexico; Gingerich Well Drilling; Grosch Irrigation; Burns & McDonnell; Black & Veatch; RW Beck; and others.

The ISEP CAES facility would use low-cost off-peak electricity to compress air, store the high-pressure air deep underground, and then release the air during high electric demand periods to drive modified combustion turbines for the generation of electricity. This CAES facility is unique when compared to the two other existing CAES operations in the world in that ISEP is intended to use an aquifer for the storage of compressed air while the plants in Huntorf, Germany, and McIntosh, Alabama, each use mined salt domes. Aquifer storage has been used successfully for over 50 years for the storage of natural gas. The ISEP plant could demonstrate the viability of aquifer storage in a CAES operation, thereby providing an analog for facilities that can be constructed in many areas where salt domes or other caverns do not exist.

Initial design concepts determined a 270-MW CAES generation plant, based on existing industry equipment, combined with 200 MW of compression equipment, would be the desired project goal. This set the parameters for cost studies, economic

feasibility studies, and geologic formation requirements.

Early searches for a suitable geologic formation in Iowa for the storage of compressed air demonstrated the challenges to be faced. The first site considered had been investigated for the storage of natural gas but experienced excessive leakage of the gas. The Iowa Geological Survey then provided records that showed 20 different dome-shaped geologic structures that might be suitable for storage of compressed gases. Researchers found over half of these were already under lease for natural gas storage. Several were too shallow or were far removed from other needed infrastructures. Two sites looked to be likely candidates.

Seismic tests on the first site selected indicated the lack of a contiguous caprock. Seismic surveys were then taken on a site near Dallas Center, Iowa, and the results looked promising, so a program for further qualification of the structure was commenced. Three exploratory wells were drilled, core samples from the wells were analyzed at SNL, and the results were analyzed with the aid of the Tough2 computer modeling software.

During the geologic study program, economic feasibility studies were also conducted. The most recent study, performed by RW Beck, concluded that ISEP at 270 MW would be cost-effective compared to conventional generation alternatives. It would also support additional wind-generation development in Iowa by consuming excess electricity for compression during lower demand periods when wind turbines might otherwise be curtailed.

The Beck analysis addressed many issues such as construction costs, intrinsic and extrinsic values, ancillary services, renewable integration to the grid, overall grid benefits from storage, and current and future MISO tariff services that will impact ISEP.

The final results from the geologic modeling preformed by The Hydrodynamics Group concluded that the low-permeability conditions in the Mt. Simon

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sandstone that was being investigated for the storage of compressed air would prevent the formation of an air bubble adequate for the successful operation of a CAES facility of 270 MW at the Dallas Center site. This led the Board of Trustees of the Iowa Stored Energy Plant Agency to make the painful decision in July 2011 to discontinue the ISEP project.

Although the site geology results were disappointing, much has been learned from the project regarding how to accomplish bulk energy storage and coordinate it with renewable wind resources. Much of these “Lessons from Iowa” are independent of geology or of the storage technology used. Accordingly, documentation of all studies conducted during the due diligence of ISEP is being prepared for presentation on the www.isepa.com web site in the near future. It is the intention of the Iowa Stored Energy Plant Agency (ISEPA) Board that the extensive work involved in the ISEP project be available to anyone interested in aquifer CAES technology, or storage technologies of all kinds.

BIOGRAPHICAL NOTE Kent Holst is the Development Director for the Iowa Stored Energy Park (ISEP). He has served in this position since the formation of the Iowa Stored Energy Plant Agency (ISEPA) in 2005. Before then he served

on the ISEP Committee of the Iowa Association of Municipal Utilities.

Mr. Holst was the General Manager of Traer, Iowa, Municipal Utilities (TMU) for 22 years until his retirement in 2004. Before joining TMU, he was a John Deere farm equipment dealer. He has a B.S. degree in Agricultural Business from Iowa State University.

http://www.isepa.com/

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SMALL-SCALE SCALABLE COMPRESSED AIR ENERGY STORAGE SYSTEM WITH THERMAL MANAGEMENT

Joseph H. Simmons, Krishna Muralidharan, George Frantziskonis, and Young-Jun Son

Arizona Research Institute for Solar Energy (AzRISE), University of Arizona, 4715 Ft. Lowell Road, Tucson, AZ, USA

Compressed air energy storage (CAES) is a promising technology for applications at sizes between utility scale and single-family home. Because of size-dependent costs and efficiencies in the expansion turbines, and in the air storage vessels, the costs do not scale with size from the utility-scale range (200 to 300 megawatts [MW]). Studies presented in this report focus on small-scale systems with thermal management. The small-scale system constructed is designed to provide 3 hours of operation at 10 kilowatts (kW) using a novel expansion turbine that is optimized to deliver high efficiency at that size. Air storage is conducted above ground in steel vessels. All components are designed to be scalable up to 10 MW.

Thermal management is practiced whereby the heat of compression from a three-stage compressor is recovered and stored, then used to heat up the compressed air before injection into the expansion turbine. This is designed to reduce consumption of natural gas in the expansion turbine. Cost analyses and optimized combinations of grid and CAES and combinations of grid, CAES, and single-axis tracking photovoltaic (PV) scenarios are presented to show the value of decreasing natural gas consumption in CAES on the economics of providing suitable energy production to meet demand on hot summer days in Tucson, Arizona.

The paper presents the following studies:

• Optimization calculations for resource mixes of grid and CAES and for grid, CAES, and single-axis tracking PV to meet demand load in summer with associated cost for producing electricity with varying avoided costs and with different natural gas consumption.

• Optimized design of a small-scale CAES system with thermal management.

• Calculated expected performance results of using the optimized design with analysis of cost.

• Measured performance of the optimized system in a grid-tied scenario and analysis of the various parts of the CAES system to determine areas of improvement.


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Poster Session 3

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211

OLIVINE AND TITANIUM OXIDE BASED LI-ION BATTERY

SYSTEM FOR STATIONARY ENERGY STORAGE

Daiwon Choi, Wei Wang, Wu Xu, and Zhenguo Yang

Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, Richland, WA, USA

ABSTRACT

Lithium (Li)-ion batteries have witnessed significant advancement the last two decades. However, despite their tremendous commercial success as a power source for consumer electronic devices in recent years, there is increasing interest in developing a high energy and power rechargeable Li-ion system for large-scale electrochemical energy storage for intermittent renewable power sources, such as solar cells and wind mill plants [1,2]. Unlike portable and vehicle applications, cycling stability and cost, along with safety, are more of importance for stationary energy storage as the requirement of weight and space is less stringent [1,2]. Recently, different combinations of positive and negative materials have been investigated for full cell performance, such as titanium dioxide (TiO2) and lithium titanate (Li4Ti5O12) [2-4]. In our study, an olivine type LiMPO4 (M: iron [Fe] or manganese [Mn]) cathode will be paired with a TiO2-based anode using some of the commercially available materials with and without surface modification and carbon mixing.

Keywords: olivine, Li-ion battery, electrochemical energy storage, renewable power sources, stationary energy storage

INTRODUCTION

Recent demands for environmental sustainability have spurred great interest in electrochemical energy storage technology [1,2]. Among the many electrochemical energy storage systems, the Li-ion battery is currently the leading technology for electric vehicles and is increasingly attractive for stationary energy storage for renewable energy resources, such as wind and solar power [1-3]. Consequently, particular interest is focused on different electrode chemistries for large-scale batteries that can satisfy more stringent requirements in cost, stability, and, most importantly, safety for successful market penetration [1-6].

Among cathode materials, olivine structured LiMPO4 (M: iron [Fe], manganese [Mn], cobalt [Co], and nickel [Ni]) cathodes deliver flat voltage, excellent cycling stability, and low entropy change throughout the state of charge (SOC) [5]. Among olivine cathodes, LiMnPO4 is a cheaper alternative to LiFePO4 with similar specific capacity (170 mAh/g) but higher voltage (4.1 volts [V] versus Li+/Li) from a Mn2+/Mn3+ redox couple within the limitations of conventional organic electrolytes [6-8]. Thus, recent works have been focused on enhancing the sluggish

electrochemical kinetics of LiMnPO4. Another important criteria for successful implementation as a cathode material is safety. Thermal instability of various charged cathodes such as layered LixMO2 (M: Co, Ni, Mn, aluminum [Al]) or spinel LixMn2O4 release O2 at elevated temperatures, leading to thermal runway where the organic electrolyte can ignite, leading to fire and explosion. However, olivine-type LiMPO4 (M: Fe, Mn, Co, Ni) cathodes have been promoted as a safe alternative due to the strong P-O covalent bonds in the tetrahedral (PO4)3− anion that inhibit oxygen loss, thereby enhancing safety for large-scale lithium (Li)-ion battery applications. Since FePO4 is reported to be stable up to 500~600 oC in air without losing oxygen, it is inferred that the charged MnPO4 compound would match the excellent thermal stability of FePO4. However, recent investigations have cast doubt on that assumption by demonstrating the possible decomposition of charged MnPO4 at 120~210 oC with evolution of O2 and heat while fully discharged LiMnPO4 remains stable up to 410 oC or higher. This is in stark contrast to FePO4. Evolution of O2 during decomposition at elevated temperatures can limit the use of LiMnPO4 as a cathode as it raises critical safety concerns [8].

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On the other hand, nanostructured titanium dioxide (TiO2) or Li4Ti5O12 has attracted much attention in Li insertion because it is not only a low-voltage insertion host for Li, but also a fast Li insertion/extraction host [9-12]. These characteristics render it a potential anode material for high-power Li-ion batteries. Lithium titanate (Li4Ti5O12) and titanium oxides (TiO2) are considered good alternatives to graphite for battery anodes. They operate at higher voltage (1.5~1.8 V versus Li+/Li) compared with graphite (0-0.5 V versus Li+/Li) and thereby provide less energy than conventional Li-ion batteries, but greatly improve the overall safety of the battery by avoiding solid-electrolyte interface (SEI) layer formation. Also, the open structures allow Li insertion/extraction without much structural straining, which can improve cycling stability.

In the present work, thermal stability with regards to phase transformation and oxygen evolution of electrochemically charged/discharged LixMnPO4 nanoplate cathodes have been analyzed. Additionally, thermal stability of the charged MnPO4 electrode has been compared with serrabrancaite MnPO4•H2O at elevated temperatures. The impact of structural stability on the safety of a high-voltage LiMnPO4 cathode is discussed. On the TiO2-based anode, improving rate performance and the gassing issue with conventional electrolyte at charged state on the commercially available Li4Ti5O12 is discussed.

RESULTS AND DISCUSSION Figure 1 shows electrochemical performance of

nanostructured LiMnPO4 cathode with close to theoretical capacity of >140 mAh/g. These LiMnPO4 electrodes at charged state were used for thermal stability studies. Figure 2 shows structural changes during heat treatment under argon (Ar) atmosphere.

2.0

2.5

3.0

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0 20 40 60 80 100 120 140 160

Disharged LiMnPO4

Volta

ge V

(vs.

Li+ /L

i)

Specific Capacity (mAh/g)

LiMnPO4 paper electrode (weight ~35mg/cm2)Rate : C/50 (CC-CV Charge)

Charged MnPO4

Fig. 1. Charge/discharge voltage profiles of LiMnPO4 nanoplate paper electrode at room temperature.

10 20 30 40 50 60 70

534oC

502oC

469oC

437oC

402oC

Inten

sity (

a.u.) 365oC

333oC

297oC

259oC

215oC

182oC

144oC

105oC

68oC

2θ

30oC

Fig. 2. In situ hot-stage XRD characterization of the charged MnPO4 electrode under UHP-Ar atmosphere ( degree of structural deformation, heating rate: 5 oC/min).

Crystal structural changes in MnPO4 started as

low as 150 oC followed by reduction into Mn2P2O7 at 490 oC under inert atmosphere. Detailed electrochemical performance LiMnPO4 and reduction process of charged MnPO4 will be presented and explained. Following our work on LiMnPO4 cathodes, olivine structured LiMn1-xFexPO4 cathodes will be optimized for stationary Li-ion battery using modified TiO2-based anodes.

ACKNOWLEDGMENTS The work is supported by the U.S. Department of

Energy (DOE), Office of Vehicle Technologies and Office of Electricity Delivery and Energy Reliability (OE). HRTEM and XPS investigations were performed in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by DOE’s Office of Biological and Environmental Research and located at PNNL is a multi-program laboratory operated by Battelle Memorial Institute for DOE under Contract DE-AC05-76RL01830.

REFERENCES [1] T. Xu, W. Wang, M. Gordin, D. Wang, and D. Choi, “Lithium ion Battery for Stationary Energy Storage,” JOM-US 62(9), 2010, pp. 24-31.

[2] Z. Yang, J. Zhang, M.C.W. Kintner-Meyer, X. Lu, D. Choi, J.P. Lemmon, and J. Liu, “Electrochemical

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Energy Storage for Green Grid,” Chemical Review, available online, 2011.

[3] D. Wang, D. Choi, J. Li, Z. Yang, Z. Nie, R. Kou, D. Hu, C. Wang, L. Saraf, J. Zhang, I.A. Aksay, and J. Liu, ACS Nano. 3, 2009, pp. 907-914.

[4] D. Choi, D. Wang, V. Viswanathan, I, Bae, W. Wang, Z. Nie, J, Zhang, G. Graff, J. Liu, Z. Yang, and T. Duong, Electrochemistry Communications 12, 2010, pp. 378-381.

[5] V.V. Vinawathan, D. Choi, D. Wang, W. Xu, S. Towne, J.-G. Zhang, J. Liu and G.Z. Yang, Journal of Power Sources 195, 2010, pp. 3720-3729.

[6] J. Xiao, W. Xu, D. Choi, and J. Zhang, Journal of the Electrochemical Society 157(2), 2010, pp. A142-A147.

[7] D. Choi, D. Wang, I.-T. Bae, J. Xiao, Zimin Nie, W. Wang, V.V. Viswanathan, Y.J. Lee, J.-G. Zhang, G.L. Graff, Z. Yang, and J. Liu, Nano Letters 10(8), 2010, pp. 2799-2805.

[8] D. Choi, J. Xiao, Y.J. Choi, J.S. Hardy, M. Vijayakumar, J. Liu, W. Xu, W. Wang, J.-G. Zhang, G. L. Graff, and Z. Yang, Energy and Environmental Science, 2011, available online.

[9] C. M. Wang, Z.G. Yang, S. Thevuthasan, J. Liu, D. R. Baer, D. Choi, D. H. Wang, W. Xu, J. G. Zhang, L. Saraf, and Z. Nie, Applied Physics Letter 94, 2009, p. 233116.

[10] G. Z. Yang, D. Choi, S. Kerisit, K.M. Rosso, D. Wang, J. Zhang, G. Graf, and J. Liu, Journal of Power Sources 192(2), 2009, pp. 588-598.

[11] D. Wang, D. Choi, J. Li, Z. Yang, Z. Nie, R. Kou, D. Hu, C. Wang, L. V. Saraf, J. Zhang, I. A. Aksay, and J. Liu, ACS Nano 3(4), 2009, pp. 907-914.

[12] D. Wang, D. Choi, V.V. Viswanathan, J. Hu, Z. Nie, C. Wang, Y. Song, G. Z. Yang, and J. Liu, Chemistry of Materials 20, 2008, pp. 3435–3442.

BIOGRAPHICAL NOTE Conference presenter: Dr. Daiwon Choi is a Staff Scientist at Pacific Northwest National Laboratory (PNNL), Energy Materials group of Energy Science and Technology Directorate. He joined PNNL in

2007 after a postdoctoral appointment at Carnegie Mellon University where he was responsible for electrode material synthesis for supercapacitors and lithium (Li)-ion batteries. He has more than 10 years of experience in material synthesis techniques. He received his B.S. and M.S. from Yonsei University of Korea and his Ph.D. from Carnegie Mellon University, where his research focused on nanostructured transition metal nitrides for supercapacitor electrodes. He was also involved in Li-ion battery research on the layered and olivine structured cathodes, Si-based anodes, biomaterials, electrochemical sensors for heavy metal detection in biological/nature water samples, and perchlorate removal using electrochemically deposited CNT/PPy nanocomposite. Dr. Choi has authored/coauthored over 40 publications in major peer-reviewed journals with eight patents pending and made numerous presentations in major conferences. His current efforts concentrate on materials synthesis and characterization in the field of Li-ion batteries for stationary and vehicle applications.

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PG&E COMPRESSED AIR ENERGY STORAGE IN CALIFORNIA

Aparna Narang

Pacific Gas & Electric Company, San Francisco, CA, USA

ABSTRACT The purpose of this presentation is to provide an overview of Pacific Gas and Electric Company’s (PG&E’s)

initiative in evaluating the technical and economic feasibility of compressed air energy storage using porous rock reservoirs in California.

GENERAL

Pacific Gas and Electric Company (PG&E) was awarded funding from the U.S. Department of Energy (DOE), the California Energy Commission (CEC), and the California Public Utilities Commission (CPUC) for the first phase of an initiative to demonstrate the technical and economic viability of advanced, underground compressed air energy storage (CAES) utilizing a porous rock reservoir. Currently, there are two utility-scale CAES facilities operating in the world, and both utilize salt domes for their storage reservoir. Due to the geology in California and many other locations in the United States, such underground storage features are not available. PG&E’s CAES project is attempting to be the first commercial CAES plant to utilize porous rock formations, such as depleted gas reservoirs for the air storage.

The work for this initiative began in February 2011 and in its first phase is focused on identification and testing of potential reservoirs in California, preliminary engineering design, and economic analysis of the facility. PG&E proposes to present an overview of the initiative, including a summary of planned project activities, criteria associated with reservoir selection, proposed reservoir testing strategy, technological characteristics under evaluation, proposed system benefits to be evaluated, and potential project challenges. The information provided below provides greater detail on the reservoir selection and testing process.

INITIAL SITE SELECTION The reservoir identification process includes a

variety of components that influence the selection of the appropriate reservoir. An overview of the site selection process will be provided in the poster

presentation. Since beginning this initiative, PG&E has evaluated approximately 70 potential sites in California based on technical, environmental, and siting criteria. Specific criteria evaluated include porosity, permeability, size, and pressure characteristics of the reservoir. The proximity to electric and gas transmission and environmental characteristics are significant factors as well. The specific metrics utilized in the evaluation process were re-assessed in the preliminary analysis and are now as follows:

Technical

• Depleted gas reservoirs • Original production of 4 BCF to 40 BCF • Permeability greater than 400 MD • Porosity greater than 15% • Pressure between 1000 and 1800 psi • Sand thickness greater than 20 feet • Low water production characteristics

Environmental/Siting

• Surface and below-ground landowner attributes

• Distance to gas and electric transmission • Air district requirements • Proximity to wetlands, flood zones, airports,

and scenic highways • Presence of sensitive species habitat • Land use

Based on these parameters, fewer than 20 sites

remain in the initial site selection process and are being vetted further before determining a short list of project sites. The primary goal of the site selection process of the PG&E CAES project is to select three sites to move into the reservoir testing phase.

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RESERVOIR TESTING PLAN The reservoir testing plan starts off with the

drilling of two test wells at each of the three short-listed sites. The core samples will be lab-tested to verify that the reservoir characteristics match the screening criteria from the desktop analysis. Based on the results of the core analyses along with other selection criteria mentioned earlier, one site will be selected for compression testing, which will include establishing an air bubble in the reservoir, followed by monitoring pressure levels and performing flow testing.

SYSTEM BENEFITS/ECONOMICS Evaluation of proposed system benefits will be a

critical activity in identifying the feasibility of CAES in the California market. Such potential benefits that will be evaluated during the first phase of the project include the ability of the potential CAES facility to provide the following: energy during on-peak periods, voltage support, area regulation, and electric supply capacity. Additionally, as part of this analysis, the economic viability of such a facility in California will be assessed based on estimated:

• Facility costs derived from the preliminary engineering design;

• Fixed and variable fuel and non-fuel operations and maintenance costs; and

• Revenue streams associated with the energy, capacity, and ancillary services this facility may provide.

FUTURE WORK

This first phase of the CAES project is scheduled to take place over approximately 4 years. Through the remainder of 2011, the project team will be focused on continued desktop evaluation of the remaining reservoirs. By the end of 2011, the goal is to have completed the desktop analysis and selected the short list of potential project sites. Ongoing throughout the course of the program is the economic analysis of the viability of a CAES plant in the California market.

In 2012 the major activities include the follow-ing:

• Site control • Preliminary plant engineering design • Commencement of drilling for core samples

In 2013 the major activities include the follow-

ing:

• Completion of drilling for core samples at three sites

• Commencement of compression testing of one reservoir

In 2014 the major activities include the follow-

ing:

• Completion of compression testing of one reservoir

• Environmental studies of selected site • Cost analysis and detailed engineering

BIOGRAPHICAL NOTE

Aparna Narang has over nine years of experience in the energy industry. She is currently the Program Manager for the $50M Compressed Air Energy Storage (CAES) initiative at the Pacific Gas & Electric Company (PG&E). Aparna also led PG&E’s wind

energy development program, growing that portfolio to over 400 MW of early stage projects. Before joining PG&E, she managed a project development portfolio of over 3,200 MW for Clipper Windpower, and managed construction planning activities for over 300 MW of wind projects at Horizon Wind Energy. She is also a graduate of General Electric’s Renewable Energy Leadership Program. Aparna has a Bachelor’s of Science in Civil Engineering and Environmental Studies from Tufts University and an MBA from the University of North Carolina at Chapel Hill.

217

CHARACTERIZATION AND ASSESSMENT OF

NOVEL BULK STORAGE TECHNOLOGIES

Poonum Agrawal,1 Ali Nourai,2 Larry Markel,1 Richard Fioravanti,2 Paul Gordon,1 Nellie Tong,2 and Georgianne Huff3

1Sentech/SRA International, Bethesda, MD, USA 2KEMA Consulting, Fairfax, VA, USA

3Sandia National Laboratories, Albuquerque, NM, USA

ABSTRACT

This paper reports the results of a high-level study to assess the technological readiness and technical and economic feasibility of 17 novel bulk energy storage technologies. The novel technologies assessed were variations of either pumped storage hydropower or compressed air energy storage. The report also identifies major technological gaps and barriers to the commercialization of each technology. Recommendations as to where future research and development efforts for the various technologies are also provided based on each technology’s technological readiness and the expected time to commercialization (short, medium, or long term).

Keywords: Pumped storage hydropower, compressed air energy storage

INTRODUCTION

The U.S. Department of Energy (DOE) commissioned this assessment of novel concepts in large-scale energy storage to aid in future program planning of its Energy Storage Program. The intent of the study is to determine if any new but still unproven bulk energy storage concepts merit government support to investigate their technical and economic feasibility or to speed their commercialization. The study focuses on compressed air energy storage (CAES) and pumped storage hydropower (PSH). It identifies relevant applications for bulk storage, defines the associated technical requirements, characterizes and assesses the feasibility of the proposed new concepts to address these requirements, identifies gaps and barriers, and recommends the type of government support and research and development (R&D) needed to accelerate the commercialization of these technologies.

BULK STORAGE APPLICATIONS AND REQUIREMENTS

The study identified six applications suitable for large-scale (over 100 MW) energy storage:

• Electric Energy Time-shift • Electric Supply Capacity • Load Following • Renewable Energy Time-shift • Renewable Capacity Firming (15 to 60, 60

to 120 minutes) • Wind Generation Grid Integration – Long

Duration

The applications technically suited and cost-effective for bulk energy storage are those with long discharge duration (on the order of hours), frequent use, deep discharge depth, response time on the order of a few minutes, with a minimum cycle life (on the order of a few thousand cycles). The technical requirements for these applications were compared to the novel technologies assessed to determine whether the technologies met the needs of the applications.

218

TECHNOLOGY CHARACTERIZATION This report characterizes 17 novel concepts in

PSH and CAES with capacities greater than 100 MW. In some cases technologies with capacities less than 100 MW are included, given the novelty of the technology or at the request of DOE. Specifically, two of the technologies included are currently available and installed in other countries. Although not novel, these technologies are included at the request of DOE because they are not commercially available in the United States.

The novel PSH technologies considered here incorporate designs with different types of reservoirs (e.g., aquifers, underground salt domes, natural gas caverns, tanks, or the ocean). Some of the novel concepts propose alternative paradigms to an upper and lower reservoir (e.g., in-ground storage pipe and in-reservoir tube); others are ocean-based (the Archimedes’ Screw and the Energy Island).

The innovations in the CAES technologies are in the storage vessel, storage medium, energy conversion process, or some other feature of the technology. Unlike traditional CAES, many of the novel technologies do not rely on underground geologic formations to store compressed air; some technologies, such as near-isothermal and underwater CAES, can store compressed air in transportable vessels or underwater bladders. The liquid air energy storage technology stores liquid instead of gas, which provides greater storage density. Other technologies, such as adiabatic and near-isothermal CAES, are considered innovative for their theoretical improvement in the efficiency of the energy conversion process. Vehicle compression and transportable CAES were included for the innovative way that they contribute to distributed generation.

The following 17 technologies assessed in this report are listed in Table 1.

Table 1. PSH and CAES Technologies Assessed. PSH Los Angeles

1. Aquifer PSH 2. Archimedes’ Screw 3. Underground Reservoir 4. Energy Island 5. In-ground Storage Pipe 6. In-reservoir Tube with

Bubbles 7. Ocean PSH 8. Variable-speed PSH

9. Adiabatic CAES 10. Adsorption-enhanced CAES 11. Diabatic CAES 12. Hydrokinetic Energy 13. Liquid Air Energy Storage 14. Near-isothermal CAES 15. Transportable CAES 16. Underwater CAES 17. Vehicle Compression

The characterization of these technologies includes both business and technical characteristics. Information for the assessment was obtained through market research and information provided by companies involved in PSH and CAES R&D.

TECHNOLOGY ASSESSMENT The technologies were evaluated using a

modified Delphi process in which five attributes were considered and given equal weight: (1) technical feasibility, (2) technical maturity, (3) engineering feasibility, (4) economic feasibility, and (5) R&D requirements. Four reviewers assessed each technology and scored each attribute on a scale of 1 to 10. The total score (5 to 50) determined the expected development time frame for the technology.

For this assessment, a score between 40 and 50 represents a technology that is expected to commercialize in the short term (5 years or less). Similarly, a technology with a score between 25 and 40 is expected to commercialize in the medium term (between 5 and 10 years). A technology with a score lower than 25 is expected to commercialize in the long term (after 10 or more years). The time frame to commercialization was also used to determine the type of government support needed to facilitate the development of the technology. Table 2 summarizes the results of the feasibility assessment.

Table 2. Time to Commercialization and Type of Government Support for Novel PSH and CAES Technologies.

Time to Commercialization

Short Term (<5 years)

Medium Term (5–10 years)

Long Term (>10 years)

Type of Govern-

ment Support

• Demonstration • Commerciali-

zation Incentives

• R&D • Demonstrations

• R&D

PSH • Ocean • Variable-speed

• Aquifer • Archimedes

Screw • Underground

• In-reservoir Tube with Bubbles

CAES • Near-isothermal

• Adiabatic • Diabatic • Liquid Air

Energy Storage • Underwater

• Adsorption-enhanced

• Hydrokinetic Energy

• Transportable • Vehicle

Compression

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In addition to the feasibility assessment, the technologies were given a technology readiness level (TRL) as defined by the DOE. The TRLs for the various PSH and CAES technologies represent the entire range (0 to 9). Such a range is indicative of the different levels of support required to reach commercialization. The general type of support recommended for each technology depends on its stage of development and how soon it is expected to be commercialized.

TECHNOLOGY GAPS, BARRIERS, AND RECOMMENDED R&D

The assessment and the TRL combined helped to determine technological gaps and barriers to commercialization for each of the technologies studied as well as the recommended focus for future R&D. As is the case with most novel technologies, they are in the very early stages of development. Indeed, because many are still in the pre-pilot phase, many companies could not provide test data for this assessment. Additionally, several of the technologies did not have any technical or cost information available. Thus, this report includes technological gaps and barriers and recommends an R&D focus for each technology to the extent possible given the limitations in the data and the early stage of development of the technologies.

In general, PSH and CAES technologies face many barriers, including

• Limited suitable locations (large bodies of water or storage space is required),

• Site-specific engineering (difficult to mass produce),

• Site permitting issues, • Long deployment time, and • Being too large for distribution-level

applications.

CONCLUSIONS This assessment serves as an initial high-level

review of novel technologies. The report characterizes and assesses the technologies and provides information on the gaps, barriers, and recommended R&D focus for each technology based on the level of information available. A more detailed assessment of selected individual technologies would be needed to

determine the extent of the required support, should DOE decide to pursue further development of any of these technologies. In general, a clear commitment and sustained interest in meeting the nation’s energy needs with the entire range of possible solutions would help facilitate the development of these technologies.

Some of the technologies may seem “futuristic” or are at early stages of development. Nevertheless, the range of technologies that were reviewed and the applications these technologies are trying to meet reflect an interest in resolving the current and future challenges facing the U.S. power system. These technologies, if developed, could help address bulk storage needs, especially as large amounts of renewable generation are integrated.

ACKNOWLEDGMENTS This work was funded and supported by the

DOE’s Office of Electricity Delivery and Energy Reliability and Office of Energy Efficiency and Renewable Energy. The authors want to thank Dr. Imre Gyuk of DOE for providing useful insights and overall direction to this project.

The authors are also appreciative of the various companies that provided helpful input on the novel pumped storage hydropower and CAES technologies assessed in this report.

BIOGRAPHICAL NOTE Conference presenter: Poonum Agrawal provides technical analysis, management, and strategic planning related to energy technology research and development (R&D), sustainability, and climate analysis. She has over 12 years of experience

in the energy and environment field, particularly on issues of data collection and analysis, microgrids R&D, electricity transmission, and market analysis. Her experience spans across the executive and legislative branches of government as well as the private sector. She has a Master’s degree in Technology Policy from MIT and a dual Bachelor’s degree in Chemical Engineering and International Relations from Tufts University.

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221

COMPRESSED AIR ENERGY STORAGE AND GEOGRAPHIC AGGREGATION: MUTUALLY REINFORCING STRATEGIES FOR INTEGRATING WIND POWER

Samir Succar1 and Robert H. Williams2 1Natural Resources Defense Council, New York, NY, USA

2Princeton Environmental Institute, Princeton University, Princeton, NJ, USA

ABSTRACT By leveraging the geographic diversity of wind energy resources, the cost and emissions of baseload wind

systems can be significantly reduced as a result of reduced capital cost requirements for balancing aggregated wind resources. Specifically, re-optimizing the compressed air energy storage (CAES) configuration, including the relative capacity of the compression and turboexpander trains as well as the storage capacity of the geologic reservoir, in response to changes in wind resource characteristics yields significant capital cost reductions for the CAES system, which translates into lower levelized costs for baseload power from wind/CAES as well as reduced carbon emission intensities.

Compressed air energy storage (CAES) is a bulk

storage technology well suited for wind-firming applications. Collocation and co-optimization of CAES and wind can enhance transmission line utilization, reduce the levelized cost of the combined system, and allow variable resources to serve a broader set of market functions. This analysis shows that the incorporation of geographic aggregation into the optimization framework for a hybrid wind/CAES baseload facility yields significant cost and performance benefits.

By leveraging the geographic diversity of wind energy resources, the cost and emissions of baseload wind systems can be significantly reduced as a result of reduced capital cost requirements for balancing aggregated wind resources. Specifically, re-optimizing the CAES configuration, including the relative capacity of the compression and turboexpander trains as well as the storage capacity of the geologic reservoir, in response to changes in wind resource characteristics yields significant capital cost reductions for the CAES system, which translates into lower levelized costs for baseload power from wind/CAES as well as reduced carbon emission intensities.

This approach results in significantly reduced carbon entry prices for Wind/CAES relative to alternative low carbon baseload systems and enables CAES to more cost-effectively balance wind output relative to conventional thermal generation. This suggests that resource aggregation and energy storage can be mutually reinforcing strategies for integrating wind and that their combination can reduce the cost

of achieving very high wind penetrations relative to the pursuit of a single integration strategy.

BIOGRAPHICAL NOTE Conference presenter: Samir Succar is part of the National Resources Defense Council’s (NRDC’s) Center for Market Innovation based in New York. Mr. Succar’s work focuses on the

integration of renewable energy and the role of transmission and distribution infrastructure upgrades, demand resources, energy storage, and other enabling technologies. Before joining NRDC, he was a member of the research staff of the Energy Systems Analysis group at the Princeton Environmental Institute of Princeton University, where his research focused on integration issues associated with utility-scale renewable energy and on enabling technologies for intermittent generation. A key focus of this work is the implementation of energy storage as a strategy for enhancing transmission infrastructure utilization and mitigating the intermittency of renewable energy with particular attention to compressed air energy storage and other bulk storage technologies. Previously Mr. Succar worked at the Princeton Macroelectronics Group developing fabrication methods for solution processed organic thin film transistors and at Schlumberger ATE developing charged particle optics for voltage contrast defect detection systems. He received a B.A. from Oberlin College and a Ph.D. in Electrical Engineering from Princeton University.

222

223

SIMULATION AND OPTIMIZATION OF A FLOW BATTERY IN AN AREA REGULATION APPLICATION

James A. Mellentine and Robert F. Savinell

Case Western Reserve University, Department of Chemical Engineering, Cleveland, OH, USA

Flow batteries have the potential to provide a

variety of grid storage services. A recent report by Sandia National Laboratories presents value propositions for energy storage in 17 distinct grid service applications, two of which are further sub-divided [1]. Flow batteries have the potential to fulfill the requirements of many of these applications. However, there is a range of flow battery types from fully decoupled power-energy capacity characteristic of redox flow batteries to hybrid flow batteries with limited decoupling of power-energy capacity. This paper focuses on the potential of flow batteries to provide area regulation ancillary grid services. Area regulation matches grid capacity with consumer demand in real time. To maintain grid voltage and frequency values within preset limits, the power capacity of the grid must be closely matched to the actual grid demand at any given time.

In this analysis we consider a hypothetical 2-megawatt (MW) generic flow battery that is simulated in an area regulation application to find the optimal energy-to-power ratio that maximizes the net present value (NPV) of a 10-year project based on a range of installation costs [2]. Using real market data obtained from the California Independent Service Operator (CAISO) [3] (e.g., see Figure 1), an optimal energy-to-power ratio for a range of battery costs is determined to maximize the NPV of this hypothetical battery installation using risk analysis software [4]. See Figure 2 for a schematic of the algorithm used for the simulation and Table 1 for a summary of simulation results. A simplified model of battery installation costs (dollars per kilowatt hour [kWh]) resulted in a positive NPV for installation costs below $400 kWh-1. For installation costs between $250 kWh-1 and $400 kWh-1, an optimal energy-to-power ratio is 1.73. The traditional advantage of decoupling power and energy capacity may not be realized in area regulation; therefore, hybrid or other low-cost flow battery chemistries such as iron-chromium or even lower-cost new developments may be more appropriate for area regulation in the future.

1000 2000 3000 4000 5000 6000 7000 8000-400

-200

0

200

400

600

Up Regulation Capacity Purchased Down Regulation Capacity Purchased

Regu

latio

n Ca

pacit

y Pu

rcha

sed

(MW

)

Hour of Year

Fig. 1. The amount of up and down regulation capacity purchased by CAISO for every hour of 2008. Positive numbers represent up regulation purchases and negative numbers represent down regulation purchases [2].

Fig. 2. Graphic representation of the simulation and optimization process used to find the optimal energy-to-power ratio of a flow battery performing an area regulation application.

224

Table 1. A Summary of Simulation Results.

Installation Cost (kWh-1)

Optimal E/P Ratio

Mean NPV

Mean IRR

Average SOC

$150 2.52 $766,900 70% 45% $200 1.93 $586,800 55% 47% $250 1.74 $437,100 40% 48% $300 1.74 $300,800 27% 48% $350 1.73 $160,500 18% 48% $400 1.73 $19,700 11% 48%

REFERENCES [1] J. Eyer and G. Corey, Energy Storage for the Electricity Grid: Benefits and Market Potential Assessment Guide, Sandia National Laboratories: Albuquerque, New Mexico, 2010.

[2] This abstract represents a paper presented at the Electrochemical Society Meeting held in Boston, Massachusetts, the week of October 9, 2011. The details of this analysis is the subject of a manuscript accepted for publication and in press of the J. Applied Electrochemistry.

[3] CAISO, 2009. Ancillary Service Information. California ISO. Available via http://oasishis.caiso.com/. Cited January 16, 2011.

[4] Palisade, 2010. @Risk risk analysis software, v5.7. Available via http://www.palisade.com/risk/. Cited January 16, 2011.

BIOGRAPHICAL NOTE Conference presenter: Robert F. Savinell is the George S. Dively Professor of Engineering at Case Western Reserve University (CWRU). He has been engaged in electrochemical engineering research and development for over 35 years with a focus on the understanding of fundamentals

and mechanisms of electrochemical systems and devices, and their design, development, and optimization. Dr. Savinell has over 100 publications and seven patents in the electrochemical field. He earned his Ph.D. in Chemical Engineering at the University of Pittsburgh, worked for the Diamond Shamrock Corporation, and taught at the University of Akron before joining CWRU in 1986. He was appointed Dean of the Case School of Engineering in 2001. In 2007 he took a one-.year sabbatical at the Massachusetts Institute of Technology as a Visiting Professor, then returned to the CWRU faculty to pursue full‐time his teaching and research interests. He is a former Director of the Yeager Center for Electrochemical Sciences, a former associate editor of the Journal of the Electrochemical Society, and a former North American editor of the Journal of Applied Electrochemistry. He is an elected Fellow of the Electrochemical Society and a Fellow of the American Institute of Chemical Engineers.

DOE ESS Program SNL Publications

http://prod.sandia.gov/sand_doc/2011/113119.pdf


226



227

DOE Energy Storage Systems Program Sandia National Laboratories (SNL) Publications

(Official “SAND” Reports) Report No. Title Authors Date

SAND 2011-3700 (not available for download yet)

Characterization and Assessment of Novel Bulk Storage Technologies

Poonum Agrawal, Ali Nourai, Larry Markel, Richard Fioravanti, Paul Gordon, Nellie Tong, and Georgianne Huff

Apr-11

Abstract: This paper reports the results of a high-level study to assess the technological readiness and technical and economic feasibility of 17 novel bulk energy storage technologies. The novel technologies assessed were variations of either pumped storage hydropower (PSH) or compressed air energy storage (CAES). The report also identifies major technological gaps and barriers to the commercialization of each technology. Recommendations as to where future R&D efforts for the various technologies are also provided based on each technology’s technological readiness and the expected time to commercialization (short, medium, or long term).

SAND2011-3119

Proton Exchange Membrane Fuel Cells for Electrical Power Generation On-Board Commercial Airplanes

Joseph W. Pratt, Leonard E. Klebanoff, Karina Munoz-Ramos, Abbas A. Akhil, Dita B. Curgus, and Benjamin L. Schenkman

May-11

Abstract: Deployed on a commercial airplane, proton exchange membrane fuel cells may offer emissions reductions, thermal efficiency gains, and enable locating the power near the point of use. This work seeks to understand whether on-board fuel cell systems are technically feasible, and, if so, if they offer a performance advantage for the airplane as a whole.

Through hardware analysis and thermodynamic and electrical simulation, we found that while adding a fuel cell system using today’s technology for the PEM fuel cell and hydrogen storage is technically feasible, it will not likely give the airplane a performance benefit. However, when we re-did the analysis using DOE-target technology for the PEM fuel cell and hydrogen storage, we found that the fuel cell system would provide a performance benefit to the airplane (i.e., it can save the airplane some fuel), depending on the way it is configured.

SAND2011-2730 Energy Storage Systems Cost Update: A Study for the DOE Energy Storage Systems Program

Susan Schoenung, Ph.D.

Apr-11

Abstract: This paper reports the methodology for calculating present worth of system and operating costs for a number of energy storage technologies for representative electric utility applications. The values are an update from earlier reports, categorized by application use parameters.


http://techlibpac.sandia.gov:8080/ipac20/ipac.jsp?session=126OP0456253M.91&profile=srn&uri=link=3100015~!461825~!3100001~!3100002&aspect=basic_search&menu=search&ri=1&source=~!horizon&term=SAND2009-6457&index=REPORTA#focus

http://infoserve.sandia.gov/sand_doc/2009/094070.pdf

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Report No. Title Authors Date

SAND2011-1009 Quantifying the Value of Hydropower in the Electric Grid: Role of Hydropower in Existing Markets

Verne W. Loose Jan-11

Abstract: The electrical power industry is facing the prospect of integrating a significant addition of variable generation technologies in the next several decades, primarily from wind and solar facilities. Overall, transmission and generation reserve levels are decreasing and power system infrastructure in general is aging. To maintain grid reliability modernization and expansion of the power system as well as more optimized use of existing resources will be required. Conventional and pumped storage hydroelectric facilities can provide an increasingly significant contribution to power system reliability by providing energy, capacity and other ancillary services. However, the potential role of hydroelectric power will be affected by another transition that the industry currently experiences—the evolution and expansion of electricity markets. This evolution to market-based acquisition of generation resources and grid management is taking place in a heterogeneous manner. Some North American regions are moving toward full-featured markets while other regions operate without formal markets. Yet other U.S. regions are partially evolved. This report examines the current structure of electric industry acquisition of energy and ancillary services in different regions organized along different structures, reports on the current role of hydroelectric facilities in various regions, and attempts to identify features of market and scheduling areas that either promote or thwart the increased role that hydroelectric power can play in the future. This report is part of a larger effort led by the Electric Power Research Institute with purpose of examining the potential for hydroelectric facilities to play a greater role in balancing the grid in an era of greater penetration of variable renewable energy technologies. Other topics that will be addressed in this larger effort include industry case studies of specific conventional and hydro-electric facilities, systemic operating constraints on hydro-electric resources, and production cost simulations aimed at quantifying the increased role of hydro.

SAND2010-4862 Selected Test Results from the Neosonic Polymer LI-ion Battery

Thomas D. Hund and David Ingersoll

Jul-10

Abstract: The performance of the Neosonic polymer Li-ion battery was measured using a number of tests including capacity, capacity as a function of temperature, ohmic resistance, spectral impedance, hybrid pulsed power test, utility partial state of charge (PSOC) pulsed cycle test, and an over-charge/voltage abuse test. The goal of this work was to evaluate the performance of the polymer Li-ion battery technology for utility applications requiring frequent charges and discharges, such as voltage support, frequency regulation, wind farm energy smoothing, and solar photovoltaic energy smoothing. Test results have indicated that the Neosonic polymer Li-ion battery technology can provide power levels up to the 10C1 discharge rate with minimal energy loss compared to the 1 h (1C) discharge rate. Two of the three cells used in the utility PSOC pulsed cycle test completed about 12,000 cycles with only a gradual loss in capacity of 10 and 13%. The third cell experienced a 40% loss in capacity at about 11,000 cycles. The DC ohmic resistance and AC spectral impedance measurements also indicate that there were increases in impedance after cycling, especially for the third cell. Cell #3 impedance Rs increased significantly along with extensive ballooning of the foil pouch. Finally, at a 1C (10 A) charge rate, the over charge/voltage abuse test with cell confinement similar to a multi cell string resulted in the cell venting hot gases at about 45°C 45 minutes into the test. At 104 minutes into the test the cell voltage spiked to the 12 volt limit and continued out to the end of the test at 151 minutes. In summary, the Neosonic cells performed as expected with good cycle-life and safety.



http://prod.sandia.gov/techlib/access-control.cgi/2008/084247.pdf

229


SAND2010-0815 Energy Storage for the Electricity Grid: Benefits and Market Potential Assessment Guide

Jim Eyer and Garth Corey

Feb-10

Abstract: This guide describes a high-level, technology-neutral framework for assessing potential benefits from and economic market potential for energy storage used for electric-utility-related applications. The overarching theme addressed is the concept of combining applications/benefits into attractive value propositions that include use of energy storage, possibly including distributed and/or modular systems. Other topics addressed include: high-level estimates of application-specific lifecycle benefit (10 years) in $/kW and maximum market potential (10 years) in MW. Combined, these criteria indicate the economic potential (in $Millions) for a given energy storage application/benefit.

The benefits and value propositions characterized provide an important indication of storage system cost targets for system and subsystem developers, vendors, and prospective users. Maximum market potential estimates provide developers, vendors, and energy policymakers with an indication of the upper bound of the potential demand for storage. The combination of the value of an individual benefit (in $/kW) and the corresponding maximum market potential estimate (in MW) indicates the possible impact that storage could have on the U.S. economy.

The intended audience for this document includes persons or organizations needing a framework for making first-cut or high-level estimates of benefits for a specific storage project and/or those seeking a high-level estimate of viable price points and/or maximum market potential for their products. Thus, the intended audience includes: electric utility planners, electricity end users, non-utility electric energy and electric services providers, electric utility regulators and policymakers, intermittent renewables advocates and developers, Smart Grid advocates.

SAND2009-6457 Benefits from Flywheel Energy Storage for Area Regulation in California — Demonstration Results

Jim Eyer Oct-09

Abstract: This report documents a high-level analysis of the benefit and cost for flywheel energy storage used to provide area regulation for the electricity supply and transmission system in California. Area regulation is an “ancillary service” needed for a reliable and stable regional electricity grid. The analysis was based on results from a demonstration, in California, of flywheel energy storage developed by Beacon Power Corporation (the system‘s manufacturer). Demonstrated was flywheel storage systems’ ability to provide “rapid-response” regulation. (Flywheel storage output can be varied much more rapidly than the output from conventional regulation sources, making flywheels more attractive than conventional regulation resources.)

SAND2009-4070 Electric Utility Transmission and Distribution Upgrade Deferral Benefits from Modular Electricity Storage

Jim Eyer Jun-09

Abstract: The work documented in this report was undertaken as part of an ongoing investigation of innovative and potentially attractive value propositions for electricity storage by the United States Department of Energy (DOE) and Sandia National Laboratories (SNL) Electricity Storage Systems (ESS) Program. This study characterizes one especially attractive value proposition for modular electricity storage (MES): electric utility transmission and distribution (T&D) upgrade deferral. The T&D deferral benefit is characterized in detail. Also presented is a generalized framework for estimating the benefit. Other important and complementary (to T&D deferral) elements of possible value propositions involving MES are also characterized.






230


SAND2008-8229 Design & Development of a 20-MW Flywheel-based Frequency Regulation Power Plant

Robert Rounds and Georgianne H. Peek

Jan-09

Abstract: This report describes the successful efforts of Beacon Power to design and develop a 20-MW frequency regulation power plant based solely on flywheels. Beacon’s Smart Matrix (Flywheel) Systems regulation power plant, unlike coal or natural gas generators, will not burn fossil fuel or directly produce particulates or other air emissions and will have the ability to ramp up or down in a matter of seconds. The report describes how data from the scaled Beacon system, deployed in California and New York, proved that the flywheel-based systems provided faster responding regulation services in terms of cost-performance and environmental impact. Included in the report is a description of Beacon’s design package for a generic, multi-MW flywheel-based, regulation power plant that allows accurate bids from a design/build contractor and Beacon’s recommendations for site requirements that would ensure the fastest possible construction. The paper concludes with a statement about Beacon’s plans for a lower cost, modular-style, modular-style substation based on the 20-MW design.

SAND2008-5583 Selected Test Results from the LiFeBatt Iron Phosphate Li-ion Battery

Thomas D. Hund and David T. Ingersoll

Sep-08

Abstract: In this paper the performance of the LiFeBatt Li-ion cell was measured using a number of tests including capacity measurements, capacity as a function of temperature, ohmic resistance, spectral impedance, high power partial state of charge (PSOC) pulsed cycling, pulse power measurements, and an over-charge/voltage abuse test. The goal of this work was to evaluate the performance of the iron phosphate Liion battery technology for utility applications requiring frequent charges and discharges, such as voltage support, frequency regulation, and wind farm energy smoothing. Test results have indicated that the LiFeBatt battery technology can function up to a 10C1 discharge rate with minimal energy loss compared to the 1 h discharge rate (1C). The utility PSOC cycle test at up to the 4C1 pulse rate completed 8,394 PSOC pulsed cycles with a gradual loss in capacity of 10 to 15% depending on how the capacity loss is calculated. The majority of the capacity loss occurred during the initial 2,000 cycles, so it is projected that the LiFeBatt should PSOC cycle well beyond 8,394 cycles with less than 20% capacity loss. The DC ohmic resistance and AC spectral impedance measurements also indicate that there were only very small changes after cycling. Finally, at a 1C charge rate, the over-charge/voltage abuse resulted in the cell venting electrolyte at 110 ºC after 30 minutes and then open-circuiting at 120 ºC with no sparks, fire, or voltage across the cell.

SAND2008-4247 Solar Energy Grid Integration Systems – Energy Storage (SEGIS-ES)

Dan T. Ton, Charles J. Hanley, Georgianne H. Peek, John D. Boyes

Jul-08

Abstract: This paper describes the concept for augmenting the SEGIS Program (an industry-led effort to greatly enhance the utility of distributed PV systems) with energy storage in residential and small commercial applications (SEGIS-ES). The goal of SEGIS-ES is to develop electrical energy storage components and systems specifically designed and optimized for grid-tied PV applications. This report describes the scope of the proposed SEGIS-ES Program and why it will be necessary to integrate energy storage with PV systems as PV-generated energy becomes more prevalent on the nation’s utility grid. It also discusses the applications for which energy storage is most suited and for which it will provide the greatest economic and operational benefits to customers and utilities. Included is a detailed summary of the various storage technologies available, comparisons of their relative costs and development status, and a summary of key R&D needs for PV-storage systems. The report concludes with highlights of areas where further PV-specific R&D is needed and offers recommendations about how to proceed with their development.





231


SAND2008-0978 Benefit/Cost Framework for Evaluating Modular Energy Storage

Susan M. Schoenung and Jim Eyer

Feb-08

Abstract: The work documented in this report represents another step in the ongoing investigation of innovative and potentially attractive value propositions for electricity storage by the United States Department of Energy (DOE) and Sandia National Laboratories (SNL) Energy Storage Systems (ESS) Program. This study uses updated cost and performance information for modular energy storage (MES) developed for this study to evaluate four prospective value propositions for MES. The four potentially attractive value propositions are defined by a combination of well-known benefits that are associated with electricity generation, delivery, and use. The value propositions evaluated are: 1) transportable MES for electric utility transmission and distribution (T&D) equipment upgrade deferral and for improving local power quality, each in alternating years, 2) improving local power quality only, in all years, 3) electric utility T&D deferral in year 1, followed by electricity price arbitrage in following years; plus a generation capacity credit in all years, and 4) electric utility end-user cost management during times when peak and critical peak pricing prevail.

SAND2007-4268

Remote Area Power Supply (RAPS) Load and Resources Profiles

Ndeye Fall, Lauren Giles, Brian Marchionini, Edward Skolnik

Jul-07

Abstract: In 1997, an international team interested in the development of Remote Area Power Supply (RAPS) systems for rural electrification projects around the world was organized by the International Lead Zinc Research Organization (ILZRO) with the support of Sandia National Laboratories (SNL). The team focused on defining load and resource profiles for RAPS systems. They identified single family homes, small communities, and villages as candidates for RAPS applications, and defined several different size/power requirements for each. Based on renewable energy and resource data, the team devised a “strawman” series of load profiles. A RAPS system typically consists of a renewable and/or conventional generator, power conversion equipment, and a battery. The purpose of this report is to present data and information on insolation levels and load requirements for “typical” homes, small communities, and larger villages around the world in order to facilitate the development of robust design practices for RAPS systems, and especially for the storage battery component. These systems could have significant impact on areas of the world that would otherwise not be served by conventional electrical grids.

SAND2007-4253 Long vs. Short-Term Energy Storage: Sensitivity Analysis

Susan M. Schoenung and William Hassenzahl

Jul-07

Abstract: This report extends earlier work to characterize long-duration and short-duration energy storage technologies, primarily on the basis of life-cycle cost, and to investigate sensitivities to various input assumptions. Another technology – asymmetric lead-carbon capacitors – has also been added. Energy storage technologies are examined for three application categories – bulk energy storage, distributed generation, and power quality – with significant variations in discharge time and storage capacity. Sensitivity analyses include cost of electricity and natural gas, and system life, which impacts replacement costs and capital carrying charges. Results are presented in terms of annual cost, $/kW-yr. A major variable affecting system cost is hours of storage available for discharge.

SAND2007-3580 Installation of the First Distributed Energy Storage System (DESS) at American Electric Power (AEP)

Ali Nourai Jun-07

Abstract: AEP studied the direct and indirect benefits, strengths, and weaknesses of distributed energy storage systems (DESS) and chose to transform its entire utility grid into a system that achieves optimal integration of both central and distributed energy assets. To that end, AEP installed the first NAS battery-based, energy storage system in North America. After one year of operation and testing, AEP has concluded that, although the initial costs of DESS are greater than conventional power solutions, the net benefits justify the AEP decision to create a grid of DESS with intelligent monitoring, communications, and control, in order to enable the utility grid of the future. This report details the site selection, construction, benefits and lessons learned of the first installation, at Chemical Station in North Charleston, WV.





232


SAND2006-6740 NAS® Battery Demonstration at American Electric Power

Benjamin L. Norris, Jeff Newmiller, Georgianne Peek

Mar-07

Abstract: The first U.S. demonstration of the NGK sodium/sulfur battery technology was launched in August 2002 when a prototype system was installed at a commercial office building in Gahanna, Ohio. American Electric Power served as the host utility that provided the office space and technical support throughout the project. The system was used to both reduce demand peaks (peak-shaving operation) and to mitigate grid power disturbances (power quality operation) at the demonstration site. This report documents the results of the demonstration, provides an economic analysis of a commercial sodium/sulfur battery energy storage system at a typical site, and describes a side-by-side demonstration of the capabilities of the sodium/sulfur battery system, a lead-acid battery system, and a flywheel-based energy storage system in a power quality application.

SAND2005-7069 Estimating Electricity Storage Power Rating and Discharge Duration for Utility Transmission and Distribution Deferral

Jim Eyer, Joe Iannucci, Paul C. Butler

Nov-05

Abstract: This report describes a methodology for estimating the power and energy capacities for electricity energy storage systems that can be used to defer costly upgrades to fully overloaded, or nearly overloaded, transmission and distribution (T&D) nodes. This “sizing” methodology may be used to estimate the amount of storage needed so that T&D upgrades may be deferred for one year. The same methodology can also be used to estimate the characteristics of storage needed for subsequent years of deferral.

SAND2005-4366 Final Report on testing of ACONF Technology for the US Coast Guard National Distress Systems

Garth P. Corey, Jerry W. Ginn, Tom M. Byrd, Leanne M. Storey, Aaron T. Murray, Philip C. Symons

Aug-05

Abstract: This report documents the results of a six month test program of an Alternative Configuration (ACONF) power management system design for a typical United States Coast Guard (USCG) National Distress System (NDS) site. The USCG/USDOE funded work was performed at Sandia National Laboratories to evaluate the effect of a Sandia developed battery management technology known as ACONF on the performance of energy storage systems at NDS sites. This report demonstrates the savings of propane gas, and the improvement of battery performance when utilizing the new ACONF designs. The fuel savings and battery performance improvements resulting from ACONF use would be applicable to all current NDS sites in the field. The inherent savings realized when using the ACONF battery management design was found to be significant when compared to battery replacement and propane refueling at the remote NDS sites.

SAND2005-0372 Evaluation of Battery/Microturbine Hybrid Energy Storage Technologies at the University of Maryland

Mindi Farber de Anda, Ndeye K. Fall

Mar-05

Abstract: This study describes the technical and economic benefits derived from adding an energy storage component to an existing building cooling, heating, and power system that uses microturbine generation to augment utility-provided power. Three different types of battery energy storage were evaluated: flooded lead-acid, valve-regulated lead-acid, and zinc/bromine. Additionally, the economic advantages of hybrid generation/storage systems were evaluated for a representative range of utility tariffs. The analysis was done using the Distributed Energy Technology Simulator developed for the Energy Storage Systems Program at Sandia National Laboratories by Energetics, Inc. The study was sponsored by the U.S. DOE Energy Storage Systems Program through Sandia National Laboratories and was performed in coordination with the University of Maryland’s Center for Environmental Energy Engineering




233


SAND2004-6177 Energy Storage Benefits and Market Analysis Handbook

James M. Eyer, Joseph J. Iannucci, Garth P. Corey

Dec-04

Abstract: This Guide describes a high level, technology-neutral framework for assessing potential benefits from and economic market potential for energy storage used for electric utility-related applications. In the United States use of electricity storage to support and optimize transmission and distribution (T&D) services has been limited due to high storage system cost and by limited experience with storage system design and operation. Recent improvement of energy storage and power electronics technologies, coupled with changes in the electricity marketplace, indicate an era of expanding opportunity for electricity storage as a cost-effective electric resource. Some recent developments (in no particular order) that drive the opportunity include: 1) states’ adoption of the renewables portfolio standard (RPS), which may increased use of renewable generation with intermittent output, 2) financial risk leading to limited investment in new transmission capacity, coupled with increasing congestion on some transmission lines, 3) regional peaking generation capacity constraints, and 4) increasing emphasis on locational marginal pricing (LMP).

SAND2004-0914 Reliability of Valve-Regulated Lead-Acid Batteries for Stationary Applications

Mindi Farber DeAnda, Jennifer Miller, Patrick Moseley, Paul Butler

Mar-04

Abstract: A survey has been carried out to quantify the performance and life of over 700,000 valveregulated lead-acid (VRLA) cells, which have been or are being used in stationary applications across the United States. The findings derived from this study have not identified any fundamental flaws of VRLA battery technology. There is evidence that some cell designs are more successful in float duty than others. A significant number of the VRLA cells covered by the survey were found to have provided satisfactory performance.

SAND2004-0372 Evaluation of Battery/Microturbine Hybrid Energy Storage Technologies at the University of Maryland

Mindi Farber DeAnda, Ndeye K. Fall

Oct-04

Abstract: This study describes the technical and economic benefits derived from adding an energy storage component to an existing building cooling, heating, and power system that uses microturbine generation to augment utility-provided power. Three different types of battery energy storage were evaluated: flooded lead-acid, valve-regulated lead-acid, and zinc/bromine. Additionally, the economic advantages of hybrid generation/storage systems were evaluated for a representative range of utility tariffs. The analysis was done using the Distributed Energy Technology Simulator developed for the Energy Storage Systems Program at Sandia National Laboratories by Energetics, Inc. The study was sponsored by the U.S. DOE Energy Storage Systems Program through Sandia National Laboratories and was performed in coordination with the University of Maryland’s Center for Environmental Energy Engineering.

SAND2003-2783 Long vs. Short-Term Energy Storage Technologies Analysis: A Life Cycle Cost Study

Susan M. Schoenung and William V. Hassenzahl

Aug-03

Abstract: This report extends an earlier characterization of long-duration and short-duration energy storage technologies to include life-cycle cost analysis. Energy storage technologies were examined for three application categories–bulk energy storage, distributed generation, and power quality–with significant variations in discharge time and storage capacity. More than 20 different technologies were considered and figures of merit were investigated including capital cost, operation and maintenance, efficiency, parasitic losses, and replacement costs. Results are presented in terms of levelized annual cost, $/kW-yr. The cost of delivered energy, cents/kWh, is also presented for some cases. The major study variable was the duration of storage available for discharge.

http://infoserve.sandia.gov/sand_doc/2002/023201j.pdf




234


SAND2003-2546 Innovative Applications of Energy Storage in a Restructured Electricity Marketplace Phase III Final Report

Joe Iannucci, Jim Eyer, Bill Erdman

Mar-05

Abstract: This report describes Phase I11 of a project entitled Innovative Applications ofEnergy Storage in a Restructured Electricity Marketplace. For this study, the authors assumed that it is feasible to operate an energy storage plant simultaneously for two primary applications: 1) energy arbitrage, i.e., buy-low-sell-high, and 2) to reduce peak loads in utility “hot spots” such that the utility can defer their need to upgrade transmission and distribution (T&D) equipment. The benefits from the arbitrage plus T&D deferral applications were estimated for five cases based on the specific requirements of two large utilities operating in the Eastern U.S. A number of parameters were estimated for the storage plant ratings required to serve the combined application: power output (capacity) and energy discharge duration (energy storage). In addition to estimating the various financial expenditures and the value of electricity that could be realized in the marketplace, technical characteristics required for grid-connected distributed energy storage used for capacity deferral were also explored.

SAND2003-0362 Innovative Business Cases for Energy Storage in a Restructured Electricity Marketplace

J. Iannucci, J. Eyer, Paul C. Butler

Feb-03

Abstract: This report describes the second phase of a project entitled Innovative Business Cases for Energy Storage in a Restructured Electricity Marketplace. During part one of the effort, nine “Stretch Scenarios” were identified. They represented innovative and potentially significant uses of electric energy storage. Based on their potential to significantly impact the overall energy marketplace, the five most compelling scenarios were identified. From these scenarios, five specific “Storage Market Opportunities” (SMOs) were chosen for an in-depth evaluation in this phase. The authors conclude that some combination of the Power Cost Volatility and the T&D Benefits SMOs would be the most compelling for further investigation. Specifically, a combination of benefits (energy, capacity, power quality and reliability enhancement) achievable using energy storage systems for high value T&D applications, in regions with high power cost volatility, makes storage very competitive for about 24 GW and 120 GWh during the years of 2001 and 2010.

SAND2002-4084 Technical and Economic Feasibility of Applying Used EV Batteries in Stationary Applications

Erin Cready, John Lippert, Josh Pihl, Irwin Weinstock, Philip C.Symons, Rudy Jungst

Mar-03

Abstract: The technical and economic feasibility of applying used electric vehicle (EV) batteries in stationary applications was evaluated in this study. In addition to identifying possible barriers to EV battery reuse, steps needed to prepare the used EV batteries for a second application were also considered. Costs of acquiring, testing, and reconfiguring the used EV batteries were estimated. Eight potential stationary applications were identified and described in terms of power, energy, and duty cycle requirements. Costs for assembly and operation of battery energy storage systems to meet the requirements of these stationary applications were also estimated by extrapolating available data on existing systems. The calculated life cycle cost of a battery energy storage system designed for each application was then compared to the expected economic benefit to determine the economic feasibility. Four of the eight applications were found to be at least possible candidates for economically viable reuse of EV batteries. These were transmission support, light commercial load following, residential load following, and distributed node telecommunications backup power. There were no major technical barriers found, however further study is recommended to better characterize the performance and life ofused EV batteries before design and testing of prototype battery systems.



235


SAND2002-3201J Correlation of Arrhenius Behavior in Power and Capacity Fades with Cell Impedance and Heat Generation in Cylindrical Lithium-ion Cells

Bor Yann Liaw, Emanuel P. Roth, Rudolph G. Jungst, G. Nagasubramanian, Herbert L. Case, Daniel H. Doughty

Aug-02

Abstract: A series of cylindrical 18650 lithium-ion cells with an MAG-10 I 1.2 M LiPF6 EC (ethylene carbonate): EMC (ethyl methyl carbonate) (w/w=3:7) 1 Li,Nio.sCoo.lsAlo.os02 configuration were made and tested for power-assist hybrid electric vehicle (HEV) applications under various aging conditions of temperature and state-of-charge (SOC). The cells were intermittently characterized for changes in power capability, rate capacity, and impedance as aging progressed. The changes of these properties with temperature, as depicted by Arrhenius equations, were analyzed, We found that the degradation in power and capacity fade seems to relate to the impedance increase in the cell. The degradation follows a multi-stage process. The initial stage of degradation has an activation energy on the order of 50-55 kJ/mol, as derived from power fade andC 1 capacity fade measured at C/1 rate. In addition, microcalorimetry was performed on two separate unaged cells at 80% SOC at various temperatures to measure static heat generation in the cells. We found that the static heat generation has an activation energy on the order of 48-55 kJ/mol, similar to those derived from power andC 1 capacity fade. The correspondence in the magnitude of the activation energy suggests that the power and C1 capacity fades were related to the changes of the impedance in the cells, most likely via the samefading mechanism. The fading mechanism seemed to be related to the static heat generation of the cell.

SAND2002-1532J Battcon 2002: A Perspective Garth P. Corey and Jack Mack

May-02

Abstract: (Not available at this time)

SAND2002-1314 Energy Storage Opportunities Analysis Phase II Final Report

P. C. Butler May-02

Abstract: This study on the opportunities for energy storage technologies determined electric utility application requirements, assessed the suitability of a variety of storage technologies to meet the requirements, and reviewed the compatibility of technologies to satisfy multiple applications in individual installations. The study is called "Opportunities Analysis" because it identified the most promising opportunities for the implementation of energy storage technologies in stationary applications. The study was sponsored by the U.S. DOE Energy Storage Systems Program through Sandia National Laboratories and was performed in coordination with industry experts from utilities, manufacturers, and research organizations. This Phase II report updates the Phase I analysis performed in 1994.

SAND2002-0751 Boulder City Battery Energy Storage Feasibility Study

Garth P. Corey, Larry E. Stoddard, Ryan M. Kerschen

Mar-02

Abstract: Sandia National Laboratories and Black & Veatch, Inc., conducted a system feasibility study to examine options for placing at Boulder City, Nevada an advanced energy storage system that can store off-peak, hydroelectric generated electricity for use during on-peak times. It evaluated the feasibility and economic impact of an energy storage demonstration project currently under consideration for the Municipal Utility Power Company for the City of Boulder City. The study included evaluations of a proposed site and appropriate advanced battery technologies, pre-conceptual design, artist’s conceptions, seasonal electricity load profiles, cost estimates for the battery storage system plus site development and operating costs, and an economic evaluation of the site’s payback potential. The study concluded that the Boulder City site is a viable candidate for a Demonstration Unit of an advanced Battery Energy Storage System (BESS) utilizing either Sodium Sulfur, Vanadium Redox, or Zinc Bromine and Regenesys® technologies and that it would provide a net value to the City of Boulder.




http://infoserve.sandia.gov/sand_doc/2000/001734z.pdf

236


SAND2001-3188 Development of the Capabilities to Analyze the Vulnerability of Bulk Power Systems

David Knusman, David Tobinson, Salvador Rodriguez, Rudolph Jungst, Angel Urbina, Thomas Paez, Satish Ranade

Oct-01

Abstract: The electrical grids of North America are an extremely large and complex set of interconnected networks vital to the economic lifeblood and safety of more than 380 million people. These networks are dynamic and constantly changing systems whose operation is vulnerable to significant disruptions due to evolving energy policies as well as from natural and man-made sources. The President's Commission on Critical Infrastructure Protection has identified electric power as a critical infrastructure sector. The 1996 blackouts of the western power system demonstrated the weaknesses of the current power grid reliability analysis tools and highlighted the need for improved techniques to deal with the uncertainties associated with the operation of a bulk power network. An alternative approach involves probabilistic load-flow characterization and is closely related to the analysis methods being developed as part of the nuclear weapon system stockpile surveillance program. Integration of the new probabilistic load-flow analysis techniques and sensitivity analysis methods will provide the tools necessary to statistically characterize the load shedding at each major bus in a very large bulk power system. By probabilistically characterizing the amount of load shed at each network node and then relating this measure to the sensitivity of the grid to failure of this node, the reliability of the grid can be understood more thoroughly. The major objective of this effort was the integration of traditional load-flow analysis packages, advanced optimization methods, and state-of-the-art uncertainty analysis techniques. In parallel with this effort, we addressed issues associated with short-term energy storage devices (e.g., batteries) that might impact the overall reliability of the bulk power system. It was anticipated that a significant impediment to integrating these various tools and techniques was the size of bulk power systems that could be analyzed with this complex suite of tools. Therefore, a secondary objective was the implementation of all software analysis tools on the massively parallel computer systems at Sandia National Laboratories. These risk-based analytical tools can be used for short-term (daily) vulnerability assessment and long-term (yearly) planning for improved network security.

SAND2001-1110J Performance of Valve-Regulated Lead-Acid Batteries in Real-World Stationary Applications: Utility Installations

Paul C. Butler, Jennifer Dunleavey, Mindi Farber-Deanda, Patrick T. Moseley

Apr-01

Abstract: The electrical grids of North America are an extremely large and complex set of interconnected networks vital to the economic lifeblood and safety of more than 380 million people. These networks are dynamic and constantly changing systems whose operation is vulnerable to significant disruptions due to evolving energy policies as well as from natural and man-made sources. The President's Commission on Critical Infrastructure Protection has identified electric power as a critical infrastructure sector. The 1996 blackouts of the western power system demonstrated the weaknesses of the current power grid reliability analysis tools and highlighted the need for improved techniques to deal with the uncertainties associated with the operation of a bulk power network. An alternative approach involves probabilistic load-flow characterization and is closely related to the analysis methods being developed as part of the nuclear weapon system stockpile surveillance program. Integration of the new probabilistic load-flow analysis techniques and sensitivity analysis methods will provide the tools necessary to statistically characterize the load shedding at each major bus in a very large bulk power system. By probabilistically characterizing the amount of load shed at each network node and then relating this measure to the sensitivity of the grid to failure of this node, the reliability of the grid can be understood more thoroughly. The major objective of this effort was the integration of traditional load-flow analysis packages, advanced optimization methods, and state-of-the-art uncertainty analysis techniques. In parallel with this effort, we addressed issues associated with short-term energy storage devices (e.g., batteries) that might impact the overall reliability of the bulk power system. It was anticipated that a significant impediment to integrating these various tools and techniques was the size of bulk power systems that could be analyzed with this complex suite of tools. Therefore, a secondary objective was the implementation of all software analysis tools on the massively parallel computer systems at Sandia National Laboratories. These risk-based analytical tools can be used for short-term (daily) vulnerability assessment and long-term (yearly) planning for improved network security.







http://infoserve.sandia.gov/sand_doc/2000/000893z.pdf

237


SAND2001-0765 Characteristics and Technologies for Long vs. Short-Term Energy Storage

S.M. Schoenung Mar-01

Abstract: This report describes the results of a study on stationary energy storage technologies for a range of applications that were categorized according to storage duration (discharge time): long or short. The study was funded by the U.S. Department of Energy through the Energy Storage Systems Program. A wide variety of storage technologies were analyzed according to performance capabilities, cost projects, and readiness to serve these many applications, and the advantages and disadvantages of each are presented.

SAND2000-3083 Advanced Battery Readiness Ad Hoc Working Group Meeting: Reclamation/Recycle Sub-Working Group Supplement and Update

Rudolph G. Jungst Dec-00

Abstract: An update on the California ZEV program was presented. The most recent program review occurred in September 2000 but was not a regulatory review. This means that no changes were made to the program at that time. California rules for handling hazardous waste were also discussed. An emergency Universal Waste Rule has been adopted on an interim basis in California in order to provide a single standard. Information on recycling and life cycle costs was presented for the nickel/metal hydride and lithium-ion battery systems. For AB2 type Ni/MH batteries, the value is in the nickel and in the metal hydride alloy. In the Li-ion case, the cathode is responsible for most of the value, unless a manganese oxide cathode is used. Prices and market trends for some of the more important battery materials were reviewed. Nickel prices have recoveredf rom the depressedle vels of 1998, and have been relatively stable over the past year. Commodity recycling flow diagrams are being developed by the US Geological Survey for several metals, including nickel. A facility in Argentina that was scheduled to open last year for the production of lithium from a brine source is now permanently closed. However, lithium prices have remained relatively stable.

The operation of the INMETCO battery recycling capability was reviewed. Expansion of the cadmium recovery facility at lNMETC0 has increased capacity by 75% for that material. The complex set of factors that governs recycling economics was discussed. Lithium Technology Corporation and Pacific Lithium Ltd. will merge early next year. A membrane process developed by Pacific Lithium to purify lithium recovered from scrap batteries was discussed. The process currently operates on a laboratory scale in a batch mode, and an energy study projects that it will be cost effective. A new project by GM Ovonic to field used NiMH batteries from EVs for rural electrification in Oaxaca Mexico was described. This is primarily seen as a way to mitigate the high initial cost of this battery system. The entire Sub-Working Group discussed the status and future needs for comprehensive recycling of nickel/metal hydride and Li-ion batteries.

SAND2000-2065J Summary of Electrical Test Results for VRLA Batteries

Crow, James Terry; Francis, Imelda; Butler, Paul Charles

Aug-00

Abstract: Sandia National Laboratories conducts the Energy Storage Systems (ESS) Program for the U.S. Department of Energy (DOE). The goal of this program is to collaborate with industry in developing cost-effective electric energy storage systems for many high-value stationary applications. Under the auspices of the ESS Pro- electrical tests were performed on two VRLA batteries to compare effects of improvements, evaluate their applicability to stationmy applications, and to determine their service lives. One battery represented a baseline design, and the other an improved design resulting from a development project. The hVO 9-cell, 1050-to 1200- Ah at C/8 batteries were tested over a 7-year period using primarily a 100°/0DOD, and approximately a C/8 discharge regime. A variety of charge profiles were investigated and characterized. Both batteries reached end-of-life after several hundred cycles. This paper will describe these results, and overall life data and comparison information will be summarized.

SAND2000-1734 Development of an Abuse Tolerance Test Protocol with Continuous Gas Monitoring

Chris C Crafts, Theodore Borek III, Rudolph G Jungst, Daniel H Doughty, Curtis D Mowry

Jul-00






238


SAND2000-1733 Life Cycle Testing of High Power 18650 Lithium-ion Cells

Terry U., David Ingersoll, Chet Motloch, Vince Battaglia, Ira Bloom, Harold Haskins

Jul-00


SAND2000-1730 Diagnostic Techniques: Gas/Electrolyte/Cell Component Analysis

Rudolph G Jungst, G. Nagasubramanian, Chris C Crafts, Theodore Borek III

Jul-00


SAND2000-1550 Energy Storage Concepts for a Restructured Electric Utility Industry

Joe Iannucci and Susan Schoenung

Jul-00

Abstract: The electric utility industry in the United States is being restructured and is now evolving from a regulated monopoly to a partially competitive, partially regulated group of electricity providers. This report outlines a wide range of innovative ways in which energy storage could be advantageously used in all aspects of this electric supply system of the future, including customer-sited storage. Nine scenarios that consider the use of storage in the restructured utility industry are described. From these cenarios, four themes for guiding the economic and technical application of energy storage are presented

SAND2000-1317 Energy Storage Systems Program Report for FY99 John. D. Boyes Jun-00

Abstract: Sandia National Laboratories, New Mexico, conducts the Energy Storage Systems Program, which is sponsored by the U.S. Department of Energy’s Office of Power Technologies. The goal of this program is to develop cost-effective electric energy storage for many high-value stationary applications in collaboration with academia and industry. Sandia National Laboratories is responsible for the engineering analyses, contracted development, and testing of energy storage components and systems. This report details the technical achievements realized during fiscal year 1999.

SAND2000-1004 Operating Environment and Functional Requirements for Intelligent Distributed Control in the Electric Power Grid

Douglas C. Smathers, Abbas A. Akhil

Mar-01

Abstract: The restructuring of the U.S. power industry will surely lead to a greater dependence on computers and communications to allow appropriate information sharing for management and control of the power grid. This report describes the operating environment for system operations that control the bulk power system as it exists today including the role NERC plays in this process. Some high-level functional requirements for new approaches to control of the grid are listed followed by a description of the next research steps that are needed to identify specific information management functions.

SAND2000-0899 Diagnostic Techniques: Gas/Electrolyte/Cell Component Analysis

Rudolph Jungst, Ganesan Nagasubramanian, Chris C Crafts

Mar-00


SAND2000-0893 Zinc/Bromine Batteries Paul Butler, Phillip Eidler, Patrick Grimes, Sandra Klassen, Ronald Miles

Apr-00







239


SAND99-2691 Development of Zinc/Bromine Batteries for Load-Leveling Applications: Phase 2 Final Report

N. C. Clark, P. Eidler, P. Lex

Oct-99

Abstract: This report documents Phase 2 of a project to design, develop, and test a zinc/bromine battery technology for use in utility energy storage applications. The project was co-funded by the U.S. Department of Energy Office of Power Technologies through Sandia National Laboratories. The viability of the zinc/bromine technology was demonstrated in Phase 1. In Phase 2, the technology developed during Phase 1 was scaled up to a size appropriate for the application. Batteries were increased in size from 8-cell, 1170-cm2 cell stacks (Phase 1) to 8- and then 60-cell, 2500-cm2 cell stacks in this phase. The 2500-cm2 series battery stacks were developed as the building block for large utility battery systems. Core technology research on electrolyte and separator materials and on manufacturing techniques, which began in Phase 1, continued to be investigated during Phase 2. Finally, the end product of this project was a 100-kWh prototype battery system to be installed and tested at an electric utility.

SAND99-2570 Utility Test Results of a 2-Megawatt, 10-Second Reserve-Power System

B. L. Norris and G. J. Ball

Oct-99

Abstract: This report documents the 1996 evaluation by Pacific Gas and Electric Company of an advanced reserve-power system capable of supporting 2 MW of load for 10 seconds. The system, developed under a DOE Cooperative Agreement with AC Battery Corporation of East Troy, Wisconsin, contains battery storage that enables industrial facilities to “ride through” momentary outages. The evaluation consisted of tests of system performance using a wide variety of load types and operating conditions. The tests, which included simulated utility outages and voltage sags, demonstrated that the system could provide continuous power during utility outages and other disturbances and that it was compatible with a variety of load types found at industrial customer sites.

SAND99-2232 Lessons Learned from the Puerto Rico Battery Energy Storage System

M. Farber De Anda, J. D. Boyes, W. Torres

Sep-99

Abstract: The Puerto Rico Electric Power Authority (PREPA) installed a distributed battery energy storage system in 1994 at a substation near San Juan, Puerto Rico. It was patterned after two other large energy storage systems operated by electric utilities in California and Germany. The U.S. Department of Energy (DOE) Energy Storage Systems Program at Sandia National Laboratories has followed the progress of all stages of the project since its inception. It directly supported the critical battery room cooling system design by conducting laboratory thermal testing of a scale model of the battery under simulated operating conditions. The Puerto Rico facility is at present the largest operating battery storage system in the world and is successfully providing frequency control, voltage regulation, and spinning reserve to the Caribbean island. The system further proved its usefulness to the PREPA network in the fall of 1998 in the aftermath of Hurricane Georges. The owner-operator, PREPA, and the architect/engineer, vendors, and contractors learned many valuable lessons during all phases of project development and operation. In documenting these lessons, this report will help PREPA and other utilities in planning to build large energy storage systems

SAND99-1853 Development of Zinc/Bromine Batteries for Load-Leveling Applications: Phase 1 Final Report

P. Eidler Jul-99

Abstract: Phase 1 of the Zinc/Bromine Load-leveling Development contract (No. 40-8965) advanced zinc/bromine battery technology demonstrates that it would be appropriate for electric utilities to establish stationary energy-storage facilities. Performances of 8-cell and 100-cell laboratory batteries met or exceeded criteria that were established to address concerns observed in previous development efforts. A battery stack that remained leak free was assembled. This report details the results of the Phase 1 efforts. A leak-free battery stack was developed, and a solid technology base for larger battery designs was established. Also, using a proprietary model from Johnson Controls Battery Group,Inc., modeling to improve the integrity and performance of battery stacks was performed.






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SAND99-1483 Performance and Design Analysis of a 250-kW, Grid-Connected Battery Energy Storage System

B. L. Norris and G. J. Ball

Jun-99

Abstract: This report documents the assessment of performance and design of a 250-kW prototype battery energy storage system developed by Omnion Power Engineering Company and tested by Pacific Gas and Electric Company, both in collaboration with Sandia National Laboratories. The assessment included system performance, operator interface, and reliability. The report also discusses how to detect failed battery strings with strategically located voltage measurements.

SAND99-0883 Energy Storage Systems Program Report for FY98 P. C. Butler Apr-99

Abstract: Sandia National Laboratories, New Mexico, conducts the Energy Storage Systems Program, which is sponsored by the U.S. Department of Energy’s Office of Power Technologies. The goal of this program is to collaborate with industry in developing cost-effective electric energy storage systems for many high-value stationary applications. Sandia National Laboratories is responsible for the engineering analyses, contracted development, and testing of energy storage components and systems. This report details the technical achievements realized during fiscal year 1998.

SAND98-2019 Summary of State-of-the-Art Power Conversion Systems for Energy Storage Applications

S. Atcitty, S. Ranade, A. Gray-Fenner

Sep-98

Abstract: The power conversion system (PCS) is a vital part of many energy storage systems. It serves as the interface between the storage device, an energy source, and an AC load. This report summarizes the results of an extensive study of stateof- the-art power conversion systems used for energy storage applications. The purpose of the study was to investigate the potential for cost reduction and performance improvement in these power conversion systems and to provide recommendations for future research and development. This report provides an overview of PCS technology, a description of several state-of-the-art power conversion systems and how they are used in specific applications, a summary of four basic configurations for the power conversion systems used in energy storage applications, a discussion of PCS costs and potential cost reductions, a summary of the standards and codes relevant to the technology, and recommendations for future research and development.

SAND98-1905 Battery Energy Storage Systems Life Cycle Costs Case Studies

S. Swaminathan, N. F. Miller, R. K. Sen

Aug-98

Abstract: This report presents a comparison of life cycle costs between battery energy storage systems and alternative mature technologies that could serve the same utility-scale applications. Two of the battery energy storage systems presented in this report are located on the supply side, providing spinning reserve and system stability benefits. These systems are compared with the alternative technologies of oil-fired combustion turbines and diesel generators. The other two battery energy storage systems are located on the demand side for use in power quality applications. These are compared with available uninterruptible power supply technologies.

SAND98-1904 Analysis of the Value of Battery Energy Storage with Wind & Photovoltaic Generation to the Sacramento Municipal Utility District

H. Zaininger Aug-98

Abstract: The U.S. Department of Energy’s Energy Storage Systems Program at Sandia National Laboratories funded a study to determine the economic and operational value of battery storage to wind and photovoltaic technologies on the Sacramento Municipal Utility District system. This report presents the performance predictions and preliminary benefit-cost results for battery storage added to the Solano wind plant and the Hedge photovoltaic plant.


http://infoserve.sandia.gov/




http://infoserve.sandia.gov/sand_doc/1997/971275-2.pdf

http://infoserve.sandia.gov/sand_doc/1997/971275-2.pdf




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SAND98-1733 Energy Storage Systems Program Report for FY97 P. C. Butler Aug-98

Abstract: Sandia National Laboratories, New Mexico, conducts the Energy Storage Systems Program, which is sponsored by the U.S. Department of Energy’s Office of Utility Technologies. The goal of this program is to collaborate with industry in developing cost-effective electric energy storage systems for many high-value stationary applications. Sandia National Laboratories is responsible for the engineering analyses, contracted development, and testing of energy storage components and systems. This report details the technical achievements realized during fiscal year 1997.

SAND98-1513 Review of Power Quality Applications of Energy Storage Systems

S. Swaminathan and R. K. Sen

Jul-98

Abstract: Under the sponsorship of the U.S. Department of Energy (DOE) Office of Utility Technologies, the Energy Storage Systems Analysis and Development Department at Sandia National Laboratories contracted Sentech, Inc., to assess the impact of power quality problems on the electricity supply system. This report contains the results of several studies that have identified the cost of power quality events for electricity users and providers. The large annual cost of poor power quality represents a national inefficiency and is reflected in the cost of goods sold, reducing U.S. competitiveness. The Energy Storage Systems (ESS) Program takes the position that mitigation merits the attention of not only the DOE but affected industries as well as businesses capable of assisting in developing solutions to these problems. This study represents the preliminary stages of an overall strategy by the ESS Program to understand the magnitude of these problems so as to begin the process of engaging industry partners in developing solutions.

SAND98-0591 Renewable Generation & Storage Project Industry & Laboratory Recommendations

N.C. Clark, P. Butler, C.P. Cameron

Mar-98

Abstract: The United States Department of Energy Office of Utility Technologies is planning a series of related projects that will seek to improve the integration of renewable energy generation with energy storage in modular systems. The Energy Storage Systems Program and the Photovoltaics Program at Sandia National Laboratories conducted meetings to solicit industry guidance and to create a set of recommendations for the proposed projects. Five possible projects were identified and a “three-pronged” approach was recommended. The recommended approach includes preparing a storage technology handbook, analyzing data from currently fielded systems, and defining future user needs and application requirements.

SAND97-2926 Modeling of Battery Energy Storage in the National Energy Modeling System

S. Swaminathan, W. T. Flynn, and R. K. Sen

Dec-97

Abstract: The National Energy Modeling System (NEMS) developed by the U.S. Department of Energy’s Energy Information Administration is a well-recognized model that is used to project the potential impact of new electric generation technologies. The NEMS model does not presently have the capability to model energy storage on the national grid. The scope of this study was to assess the feasibility of, and make recommendations for, the modeling of battery energy storage systems in the Electricity Market Module of the NEMS. Incorporating storage within the NEMS will allow the national benefits of storage technologies to be evaluated.

SAND97-2700 Renewable Generation & Storage Project Industry & Laboratory Recommendations

N. C. Clark, P. C. Butler, C.P. Cameron

Mar-98

Abstract: The United States Department of Energy Office of Utility Technologies is planning a series of related projects that will seek to improve the integration of renewable energy generation with energy storage in modular systems. The Energy Storage Systems Program and the Photovoltaics Program at Sandia National Laboratories conducted meetings to solicit industry guidance and to create a set of recommendations for the proposed projects. Five possible projects were identified and a “three-pronged” approach was recommended. The recommended approach includes preparing a storage technology handbook, analyzing data from currently fielded systems, and defining future user needs and application requirements.













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SAND97-1618J Energy and Power Characteristics of Lithium-ion Cells

G. Nagasubramanian and R. G. Jungst

Jan-97

Abstract: We describe below the electrochemical performance characteristics (including charge/discharge characteristics at different rates) of 18650 and prismatic lithium-ion cells at ambient and sub-ambient temperatures. Ragone plots of power and energy data for these cells are compared and indicate that at room temperature the -500 mAh prismatic lithium-ion cells exhibit higher specific power and power density than the 18650 cells. Over the temperature range from 35°C to -20ºC, the cell impedance is almost constant for both cell types. These cells show very little voltage drop for current pulses up to 1 A. Keywords: Lithium-ion; Ragone data.

(Contact Sandia Technical Library)

T&D in Alaska: Like an Undeveloped Nation, in Electrical World

P. Taylor, M. Demarest, and P. C. Butler

Aug-97


SAND97-1276 Final Report on the Development of a 250-kW Modular, Factory-Assembled Battery Energy Storage System

G. P. Corey, W. Nerbun, D. Porter

Aug-98

Abstract: A power management energy storage system was developed for stationary applications such as peak shaving, voltage regulation, and spinning reserve. Project activities included design, manufacture, factory testing, and field installation. The major features that characterize the development are the modularity of the product, its transportability, the power conversion method that aggregates power on the AC side of the converter, and the use of commonly employed technology for system components.

SAND97-1275/2 Battery Energy Storage Market Feasibility Study–Expanded Report

A. Akhil and S. Kraft Jul-97

Abstract: Under the sponsorship of the U.S. Department of Energy’s Office of Utility Technologies, the Energy Storage Systems Analysis and Development Department at Sandia National Laboratories (SNL) contracted Frost & Sullivan to conduct a market feasibility study of energy storage systems. The study was designed specifically to quantify the battery energy storage market for utility applications. This study was based on the SNL Opportunities Analysis performed earlier. Many of the groups surveyed, which included electricity providers, battery energy storage vendors, regulators, consultants, and technology advocates, viewed battery storage as an important technology to enable increased use of renewable energy and as a means to solve power quality and asset utilization issues. There are two versions of the document available, an expanded version (approximately 200 pages, SAND97-1275/2) and a short version (approximately 25 pages, SAND97-1275/1).

SAND97-1275/1 Battery Energy Storage Market Feasibility Study A. Akhil and S. Kraft Jul-97

Abstract: Under the sponsorship of the Department of Energy’s Office of Utility Technologies, the Energy Storage Systems Analysis and Development Department at Sandia National Laboratories (SNL) contracted Frost& Sullivan to conduct a market feasibility study of energy storage systems. The study was designed specifically to quantify the energy storage market for utility applications. This study was based on the SNL Opportunities Analysis performed earlier. Many of groups surveyed, which included electricity providers, battery energy storage vendors, regulators, consultants, and technology advocates, viewed energy storage as an important enabling technology to enable increased use of renewable energy and as a means to solve power quality and asset utilization issues. There are two versions of the document available, an expanded version (approximately 200 pages, SAND97-1275/2) and a short version (approximately 25 pages, SAND97-1275/1).


Battery Storage All But Eliminates Diesel Generator, in Electrical World

M. Demarest, P. Taylor, D. Achenbach, A. A. Akhil

Jun-97







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SAND97-1136 Energy Storage Systems Program Report 1996 P. C. Butler Aug-97

Abstract: Sandia National Laboratories, New Mexico, conducts the Energy Storage Systems program, which is sponsored by the U.S. Department of Energy’s Office of Utility Technologies. The goal of this program is to assist industry in developing cost-effective energy storage systems as a resource option by 2000. Sandia is responsible for the engineering analyses, contracted development, and testing of energy storage systems for stationary applications. This report details the technical achievements realized during fiscal year 1996.

SAND97-0443 Cost Analysis of Energy Storage Systems for Electric Utility Applications

A. Akhil, R. K. Sen, S. Swaminathan

Feb-97

Abstract: Under the sponsorship of the Department of Energy, Office of Utility Technologies, the Energy Storage System Analysis and Development Department at Sandia National Laboratories (SNL) conducted a cost analysis of energy storage systems for electric utility applications. The scope of the study included the analysis of costs for existing and planned battery, SMES, and flywheel energy storage systems. The analysis also identified the potential for cost reduction of key components.


DOE’s Battery Storage Program, in Power Quality Assurance Magazine, Vol. 8, No. 1, p. 16

G. P. Corey and G. A. Buckingham

Jan-97


SAND96-2900 Photovoltaic Battery & Charge Controller Market and Applications Survey: An Evaluation of the Photovoltaic System Market for 1995

Robert Hammond, Jane F. Turpin, Garth P. Corey, Thomas D. Hund, Steve R. Harrington

Dec-96

Abstract: Under the sponsorship of the Department of Energy, Office of Utility Technologies, the Battery Analysis and Evaluation Department and the Photovoltaic System Assistance Center of Sandia National Laboratories (SNL) initiated a U.S. industry-wide PV Energy Storage System Survey. Arizona State University (ASU) was contracted by SNL in June 1995 to conduct the survey. The survey included three separate segments tailored to: a) PV system integrators, b) battery manufacturers, and c) PV charge controller manufacturers. The overall purpose of the survey was to: a) quantify the market for batteries shipped with (or for) PV systems in 1995, b) quantify the PV market segments by battery type and application for PV batteries, c) characterize and quantify the charge controllers used in PV systems, d) characterize the operating environment for energy storage components in PV systems, and e) estimate the PV battery market for the year 2000. All three segments of the survey were mailed in January 1996. This report (discusses the purpose, methodology, results, and conclusions of the survey.


Lead-Acid Batteries in Systems to Improve Power Quality, Fifth European Lead Battery Conference, Barcelona, Spain

P. C. Butler, P. Taylor, W. Nerbun

Oct-96



Energy Storage Solutions for Premium Power, in IEEE Aerospace and Electronics Systems, vol. 11, pp. 41-44

G. P. Corey Jun-96







http://www.prod.sandia.gov/cgi-bin/techlib/access-control.pl/1993/931754.pdf

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SAND96-1062 Sodium/Sulfur Battery Engineering for Stationary Energy Storage–Final Report

A. Koenig and J. Rasmussen

Apr-96

Abstract: The use of modular systems to distribute power using batteries to store off-peak energy and a state-of-the-art power inverter is envisioned to offer important national benefits. A 4-year, cost-shared contract was performed by Silent Power, Inc., to design and develop a modular, 300-kVA/300-kWh system for utility and customer applications. Called Nas-PAc, this system uses advanced sodium/sulfur batteries and requires only about 20% of the space of a lead-acidbased system with a smaller energy content. Ten, 300-VDC, 40-kWh sodium/sulfur battery packs are accommodated behind a power conversion system (PCS) envelope with integrated digital control. The resulting design facilitates transportation, site selection, and deployment because the system is quiet and non-polluting, and can be located in proximity to the load. This report contains a detailed description of the design and supporting hardware development performed under this contract.

SAND96-0532 Utility Battery Storage Systems Program Report for FY95

Paul C. Butler Mar-96

Abstract: Sandia National Laboratories, New Mexico, conducts the Utility Battery Storage Systems Program, which is sponsored by the U.S. Department of Energy’s Office of Utility Technologies. The goal of this program is to assist industry in developing cost-effective battery systems as a utility resource option by 2000. Sandia is responsible for the engineering analyses, contracted development, and testing of rechargeable batteries and systems for utility energy storage applications. This report details the technical achievements realized during fiscal year 1995.

SAND95-2287J Battery Technology Evaluation at Sandia National Laboratories

Paul C. Butler Oct-95


SAND95-0420 Utility Battery Storage Systems Program Report for FY94

Paul C. Butler Mar-95

Abstract: Sandia National Laboratories, New Mexico, conducts the Utility Battery Storage Systems program, which is sponsored by the U. S. Department of Energy’s Office of Energy Management. The goal of this program is to assist industry in developing cost-effective battery systems as a utility resource option by 2000. Sandia is responsible for the engineering analyses, contracted development, and testing of rechargeable batteries and systems for utility energy storage applications. This report details the technical achievements realized during fiscal year 1994.

SAND94-3105J Spectroelectrochemical Studies on Metallophthalocyanines Adsorbed on Electron Surfaces

David T. Ingersoll, Narayan Doddapaneni, Su-Moon Park, Bertha Ortiz, Sun-Il Mho

Dec-94

Abstract: Co(II)- and Fe(II)-phthalocyanines adsorbed on platinum and various carbon electrode surfaces have been studied by spectro-electrochemical techniques. The metallophthalocyanine (MPc) films were prepared on substrate electrodes by a drop-dry method after dissolving them in pyridine. While not much c h a n gine s pectroscopic propertiesi s observed for MPc's adsorbed at the platinum electrode, both the Soret and Q bands were significantly broadened when adsorbed on the carbon electrodes. Also, the metal-ligand charge transfer (MLCT) bands are observed from CoPc films adsorbed on carbon substrates even if they are not reduced. These observations lead to a conclusion that the MPc molecules not only undergo oligomerization but also interact strongly with carbon surfaces by perhaps sharing -electrons of carbon.







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SAND94-2605 Battery Energy Storage for Utility Applications: Phase I – Opportunities Analysis. Sandia National Laboratories

P. C. Butler Oct-94

Abstract: One of the goals of the Utility Battery Storage Systems (UBS) Program is to characterize potential electric utility applications for battery energy storage and their economic benefit. The UBS program is conducted by Sandia National Laboratories and sponsored by the U.S. Department of Energy’s Office of Energy Management. An initial analysis was performed to identify specific utility applications, to develop engineering requirements for each, to identify entry markets for specific battery technologies, and to assess national-level benefits for each application. Input was provided by representatives from utilities, battery and battery systems manufacturers, consultants, and UBS staff. The results of this study are presented in this report.

SAND94-2047 Zinc-air Technology: December 1993 Meeting Report

Nancy H. Clark and K. Kinoshita

Oct-94

Abstract: A Zinc/Air Battery Review and Strategic Planning Meeting was held in 1993. One outcome of the meeting was recognition of the need for a report on the current status of the technology. This report contains contributions from many of the attendees at the above meeting and expresses their views on where the technology is today and what could/should be done to improve its performance.

SAND93-3900 Battery Energy Storage: A Preliminary Assessment of National Benefits (The Gateway Benefits Study). Sandia National Laboratories

A. A. Akhil, et al. Dec-93

Abstract: Preliminary estimates of national benefits from electric utility applications of battery energy storage through the year 2010 are presented along with a discussion of the particular applications studied. The estimates in this report were based on planning information reported to DOE by electric utilities across the United States. Future studies are planned to refine these estimates as more application-specific information becomes available.

SAND93-2477 Battery Energy Storage and Superconducting Magnetic Energy Storage for Utility Applications: A Qualitative Analysis

Abbas A. Akhil, Paul C. Butler, Thomas C. Bickel

Nov-93

Abstract: This report was prepared at the request of the U.S. Department of Energy’s Office of Energy Management for an objective comparison of the merits of battery energy storage with superconducting magnetic energy storage technology for utility applications. Conclusions are drawn regarding the best match of each technology with these utility application requirements. Staff from the Utility Battery Storage Systems Program and the Superconductivity Programs at Sandia National Laboratories contributed to this effort.

SAND93-2023 Materials for Advanced Rechargeable Batteries Paul C. Butler and Sandra E. Klassen

Aug-93


SAND93-1754 Specific Systems Studies of Battery Energy for Electric Utilities

A. A. Akhil, L. Lachenmeyer, S.J. Jabbour, N. H. Clark

Aug-93

Abstract: Sandia National Laboratories, New Mexico, conducts the Utility Battery Storage Systems Program, which is sponsored by the U.S. Department of Energy’s Office of Energy Management. As a part of this program, four Utility-specific systems studies were conducted to identify potential battery energy storage applications within each utility network and estimate the related benefits. This report contains the results for these systems.













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SAND93-0047j “Sodium Beta Batteries,” (Handbook of Batteries, Chapter 12, McGraw Hill)

J. W. Braithwaite and W. L. Auxer

Jan-95


SAND92-2272 Utility Battery Storage Systems Programs Report for FY92

Paul C. Butler Jan-93

Abstract: Sandia National Laboratories, New Mexico conducts the Utility Battery Storage Systems Program, which is sponsored by the U.S. Department of Energy’s Office of Energy Management. In this capacity, Sandia is responsible for the engineering analyses, contract development, and testing of rechargeable batteries for utility-energy-storage applications. This report details the technical achievements realized during fiscal year 1992.

SAND91-2694 Utility Battery Exploratory Technology Development Program Report for FY-91

Nicholas Magnai, Paul Butler, Abbas Akhil, Jeffrey Braithwaite, J. Freese, Nancy Clark

Dec-91

Abstract: Sandia National Laboratories, Albuquerque, manages the Utility Battery Exploratory Technology Development Program, which is sponsored by the U.S. Department of Energy’s Office of Energy Management. In this capacity, Sandia is responsible for the engineering analyses and development of rechargeable batteries for utility-energy-storage applications. This report details the technical achievements realized during fiscal year 1991.

SAND91-1818 Characteristics and Development Report for the MC4169 Double-Layer Capacitor Assembly

Nancy H. Clark and Wes E. Baca

Sep-93

Abstract: The MC4169 Double-Layer Capacitor Assembly was developed in response to a request from the B61 Systems organization to provide interim power for the B61 Common JTA Development. The project has been successfully completed, and Lot 1 has been built by MMSC/GEND. Development testing showed that this assembly met all design requirements. This report describes the design configuration, environmental testing, and aging, reliability, and safety studies done to ensure that the design requirements were met.

SAND91-0672 Exploratory Battery Technology Development Report for FY90

Nicholas Magnani, Paul Butler, Abbas Akhil, Jeffrey Braithwaite, J. Freese, Stephen Lott

Apr-91

Abstract: Sandia National Laboratories, Albuquerque, manages the Utility Battery Exploratory Technology Development Program, which is sponsored by the U.S. Department of Energy’s Office of Energy Management. In this capacity, Sandia is responsible for the engineering analyses and development of advanced rechargeable batteries for stationary energy storage applications. This report details the technical achievements realized during fiscal year 1990.

SAND89-3039 Exploratory Battery Technology Development and Testing Report for 1988

Nicholas Magnani, Ronald Diegle, Jeffrey Braithwaite, D. Bush, Paul Butler, J. Freese, K. Grothaus, Kevin Murphy

Oct-89

Abstract: Sandia National Laboratories, Albuquerque, has been designated as Lead Center for the Exploratory Battery Technology Development and Testing Project, which is sponsored by the U.S. Department of Energy's Office of Energy Storage and Distribution. In this capacity, Sandia is responsible for the engineering development of advanced rechargeable batteries for both mobile and stationary energy storage applications. This report details the technical achievements realized in pursuit of the Lead Center's goals during calendar year 1988.

247



Glossary of Testing Terminology for Rechargeable Batteries

Paul C. Butler Oct-88



Exploratory Battery Technology Development and Testing Report for 1987

Nicholas Magnani, Ronald Diegle, Jeffrey Braithwaite, D. Bush, Paul Butler, J. Frees, K. Grothaus, Kevin Murphy

Aug-88




Nicholas Magnani, Robert Clark, Jeffrey Braithwaite, D. Bush, Paul Butler, J. Freese, K. Grothaus, Kevin Murphy, Paul Shoemaker

Feb-88




Nicholas Magnani, Robert Clark, Jeffrey Braithwaite, D. Bush, Paul Butler, J. Freese, K. Grothaus, Kevin Murphy, Paul Shoemaker

Jun-87


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SPONSORS Our sincere “THANKS!” to the companies and organizations that, over the years, have made EESAT the premier international forum for the discussion and promotion of Electrical Energy Storage. This year is no exception.

Platinum

Electricity Storage Association

Silver

A123 Systems

East Penn Manufacturing Co., Inc.

Kema

GS Battery, Inc.

NGK Insulators, Ltd.

Bronze

Ashlawn Energy

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