Colorado Fuel Cell Center
Novel Solid Oxide Flow Battery Systems for Grid-energy Storage
Rob Braun, Chris Wendel, Robert KeeDepartment of Mechanical Engineering
College of Engineering & Computational SciencesColorado School of Mines
Golden, CO USA(aes.mines.edu)
Scott Barnett, Gareth Hughes, Zhan GaoNorthwestern University
GCEP Symposium
15 October 2014
NORTHWESTERNUNIVERSITY
Advanced Energy Systems Group
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Colorado School of MinesEarth • Energy • Environment
Presentation OutlineI. Introduction
A. Solid Oxide Flow Battery (SOFB) Concept OverviewB. Motivation & Storage Requirements
II. ‘Reversible’ Solid Oxide Cells (ReSOC) as Flow BatteryA. Theory of Operation & Performance ConsiderationsB. Performance Analysis of Large-scale Systems (MW / GWh)
III. Cell Technology Research ActivitiesA. Intermediate Temperature LSGM CellsB. Durability & Cycle Endurance Testing
IV. Techno-Economics of Large-scale SOFB Systems
V. Summary & Future Activities
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Colorado School of MinesEarth • Energy • Environment
A solid oxide flow battery has similarities to a fuel cell operated ‘reversibly’ where reactants are tanked
Flow battery advantage:– Power capacity scales with size of stack– Energy scales with size of storage tanks
Solid oxide cell advantage High efficiency and high energy dense fuels
(H2O, CO2) (CH4, H2, CO) Favorable scaling
(Tank Area) (energy)2/3
Tanks filled with low-cost feedstocks: H2O and CO2
Conventional flow batteries use expensive liquid electrolyte
Fuel electrode
ElectrolyteO2-
Oxygen electrode
Fuel Storage
Feedstock Storage
Power Out
e-
Renewable Power source
e-
e-
e-
Air (O2)
Fuel cell mode
Electrolysis mode
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Colorado School of MinesEarth • Energy • Environment
The variability of renewable energy resources is motivating development of grid-energy solutions
Wind power variability PV, CSP (power fall-off in evening) Current battery technology is not
ready yet Migration towards thermal batteries
for VER (Hawaii) and via market arbitrage (Minnesota 1-GWh batt)
Peak Day Wind, Hawaii Oct. 20101
1Y. Kawanami, Hawaiian Electric Power Co., ASHRAE Summer Meeting, 2013
Long-term U.S. DOE Specified Targets2:Capital cost: 150 $/kWhRoundtrip Efficiency: ~80%Levelized cost: 0.10 $/kWh-cycCycles: 5,000Storage duration: 1-12 hr
Trends & Challenges
2U.S.Dept. of Energy, Grid Energy Storage Report, Dec. (2013)
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Colorado School of MinesEarth • Energy • Environment
Presentation OutlineI. Introduction
A. Solid Oxide Flow Battery (SOFB) Concept OverviewB. Motivation & Storage Requirements
II. ‘Reversible’ Solid Oxide Cells (ReSOC) as Flow BatteryA. Theory of Operation & Performance ConsiderationsB. Performance Analysis of Large-scale Systems (MW / GWh)
III. Cell Technology Research ActivitiesA. Intermediate Temperature LSGM CellsB. Durability & Cycle Endurance Testing
IV. Techno-Economics of Large-scale SOFB Systems
V. Summary & Future Activities
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Colorado School of MinesEarth • Energy • Environment
A voltage-current plot is the cell’s performance characteristic, but system roundtrip efficiency is critical
,powergenerated SOFCpowerconsumed SOEC
(iFC=iEC for continuous operation)
,
∗ ,∗ ,
Roundtrip System Efficiency:
Roundtrip Stack Efficiency:
Overpotential
How can we improve system efficiency?1. Reduce overpotential (cell/stack performance)2. Reduce balance of plant power (system design & operation)
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Colorado School of MinesEarth • Energy • Environment
Stack thermal management improves with internal reforming/generation of methane
Fuel cell requires heat rejectionElectrolysis requires heat supply
Highly endothermic!
Highly exothermic!
Methanation promoted by:–Low temperature–High pressure
SOEC mode reactions
650°C
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Fuel composition must consider… Carbon deposition Allowable fuel utilization Fuel energy density Methane content (exothermicity)
Selecting the Fuel Cell / Electrolysis ‘tank’ gas composition involves many considerations
TOP: C-H-O composition space for reversible coke-free operation
– Gas mixture neither fully oxidized nor fully reduced in ReSOCs
BOTTOM: Equilibrium gas constitution versus position along stack– Produce 60/40 CH4-H2 mixture– Oxygen content ranges 4-40%
enabling high storage capacity
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Colorado School of MinesEarth • Energy • Environment
A proposed application for energy storage with SOFBs is large-scale underground cavern storage of CO2 and CH4
An example large-scale storage concept in Denmark
Underground caverns store CH4 and CO2
500 GWh storage
Systems at these scales could achieve low cost storage (3-4 ȼ/kWh) with long storage times (months)
ReSOC also suitable for Power-to-Gas platform currently underway in Europe
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Colorado School of MinesEarth • Energy • Environment
Large-scale energy storage (~GWh) would require large tanks (or caverns) and balance-of-plant
Electric grid
Wind
Systems integration and thermal management are critical to viable SOFB storage systems
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Colorado School of MinesEarth • Energy • Environment
Constant cell ASR optimization study on T, p, utilization Parametric studies* indicate optima of cell temp., press., and utilization
System efficiency combines contributions of stack performance and balance of plant (BOP)
*C.H. Wendel and R.J. Braun, Proc. ASME 12th Fuel Cell Sci. Eng. and Tech. Conference, ESFuelCell 2014, June 29-July 2, Boston USA.
Optima:P = 20 barT = 675°CUtilization = 74%
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Colorado School of MinesEarth • Energy • Environment
Presentation OutlineI. Introduction
A. Solid Oxide Flow Battery (SOFB) Concept OverviewB. Motivation & Storage Requirements
II. ‘Reversible’ Solid Oxide Cells (ReSOC) as Flow BatteryA. Theory of Operation & Performance ConsiderationsB. Performance Analysis of Large-scale Systems (MW / GWh)C. Distributed-scale Systems (kW / MWh)
III. Cell Technology Research ActivitiesA. Intermediate Temperature LSGM CellsB. Durability & Cycle Endurance Testing
IV. Techno-Economics of Large-scale SOFB Systems
V. Summary & Future Activities
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Colorado School of MinesEarth • Energy • Environment
Cell description– (La,Sr)(Co,Fe)O3 (LSCF)
composite air electrode– Thin (La,Sr)(Ga,Mg)O3
(LSGM) electrolyte– Ni-infiltrated porous LSGM
fuel electrode– (Sr,La)TiO3 (SLT) support
Next generation ReSOC Intermediate temp. (600-650°C) Pressurized, Coke resistant Cyclability (electrical, thermal) LSGM cell technology*
Next generation material sets for ReSOCs are targeting lower temperature operation
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High cell performance in both operating modes is achieved with LSGM cells
*Zhan, et al., RSC Advances 2, 4075, (2012).
Record power density: 1.6 Wcm-2 @ 650C
Area Specific Resistance: 0.18 Ωcm2 at 650oC Still need better 600°C performance
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Effect of Current Switching On Durability
Symmetrical cells tested at 800°C– (La,Sr)MnO3-YSZ electrodes– YSZ electrolyte– 1 hour period current switching
Degradation with current switching is less than for dc electrolysis!
No measurable degradation at ≤ 0.8 A/cm2
Fast degradation at 1.5 A/cm2
– Current cycling degradation mechanism similar to electrolysis degradation
*Hughes, et al., Phys. Chem. Chemical Phys.,15, (2013)
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Colorado School of MinesEarth • Energy • Environment
Presentation OutlineI. Introduction
A. Solid Oxide Flow Battery (SOFB) Concept OverviewB. Motivation & Storage Requirements
II. ‘Reversible’ Solid Oxide Cells (ReSOC) as Flow BatteryA. Theory of Operation & Performance ConsiderationsB. Performance Analysis of Large-scale Systems (MW / GWh)
III. Cell Technology Research ActivitiesA. Intermediate Temperature LSGM CellsB. Durability & Cycle Endurance Testing
IV. Techno-Economics of Large-scale SOFB Systems
V. Summary & Future Activities
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Colorado School of MinesEarth • Energy • Environment
Two methods of economic evaluation were employed which demonstrate SOFB viability
1. Simple Calculation* – Investment cost, storage, cycles and efficiency
StorageCost$ CapitalCost $
Energy kWh ∙ Life cycles ∙ Efficiency
Assumes 100% capacity factor (i.e., always operating)
Capital Costing – Leverage SOFC CAPEX estimations in literature
Parameter Value CommentSOFB System Rating 250 MW CSM design @70% RT efficiency ReSOC Life 5–yrs Mature technology projectionBalance of Plant Life 20-yrsStorage 500 GWh 2,000-h @ 250 MW ratedCO2/CH4 Caverns 120 million m3 Lille Torup, DK facility basis
*Yang et al., Chem. Rev. 111, 3577-3613 (2011)
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Colorado School of MinesEarth • Energy • Environment
Capital cost $1075/kW(2013 US$)
Simple costing method = 2.8 ȼ/kWh storage cost
Bottom-up total plant costing indicates low capital cost and competitive storage costs
(SOFB)
Total Expense Breakdown
Jensen, Graves, Wendel, Braun, Barnett, Hughes et al., submitted to Science (2014)
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Electricity arbitrage shows higher storage cost, but substantial revenue with in future scenario
2008 Scenario: Actual capacity factor = 61% (not 100%)
(2211 hrs sell ; 3159 hrs buy)
Net cost of storage = 3.7 ȼ/kWh (4 ȼ/kW revenue)
2050 Scenario: Forecasted 2050 prices under 100%
renewables penetration much greater price volatility
Annual revenue of storage = 9.3 ȼ/kWh
Jensen, Graves, Wendel, Braun, Barnett, Hughes et al., submitted to Science (2014)
2. Electricity Arbitrage – Revenue model which estimates maximum annual income based on historic prices of Danish electricity spot market
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Colorado School of MinesEarth • Energy • Environment
The potential markets for SOFB storage technology span numerous storage applications and even fuel production
Much work yet remains for ReSOC/SOFB development including: Advanced cell development towards 600°C Scale-up Long-term stability and durability testing Systems integration & Dynamic operation
SOFBSOFB
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Colorado School of MinesEarth • Energy • Environment
Cell / Systems SOFB systems have potential for roundtrip efficiencies >73% (Large)
and 70-78% (Distributed-scale) System efficiency can increase to >80% when considering thermal
integration with other heat sources (CSP, Nuclear, Synfuels,…) Cell material advancements (LSGM architectures) and degradation/cycle
durability show an attractive development trajectory
Techno-economics Large systems (250 MW) could achieve ~3 ȼ/kWh storage ($1075/kW) Electricity arbitrage models suggest storage revenue is a possibility Regardless of estimation approach, cost estimates show ReSOC
technology can meet or exceed DOE storage cost requirements
ReSOCs have the potential to work as highly efficient energy storage devices in numerous market applications
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Acknowledgements
Funding: Stanford GCEP
Dr. Pejman Kazempoor, CSM Post-Doc (now at GE)
Drs. Soren Jansen, Chris Graves, and Mogens Mogensen (DTU)
