Renewable Energy Issues
University of Colorado at BoulderDepartment of Electrical, Computer, and Energy EngineeringEnergy Storage Research Group
Energy Storage and The Integration of Renewable Energy Into The Gridhttp://www.colorado.edu/engineering/energystorage/Frank S [email protected]
AcknowledgementsJonah Levine Michelle LimMohit ChhabraBrad LutzGreg MartinMuhammad AwanTaha HarnesswalaThe work leading to this talk was conducted by
2Richard MoutouxCamelia BoufKimberly Newman 23Outline of Our Work1. Potential Location of Pumped Hydroelectric Storage in Colorado2. Issues in Compressed Air Storage at 1500m in Eastern Colorado3. The use of battery storage for frequency control and voltage regulation4. Feed In Angle for Solar Power5. The Optimization of Energy Use in Water Systems. 6. Detection of Power Theft7. Optimization of Energy Use in Water Systems
Obstacles to Integration of Wind and Solar EnergyThe Variability of Wind, Solar and Hydroelectric Power and Mismatch to the LoadsThe Integration and Control of a Large Number of Distributed Sources in to the GridLack of low cost convenient energy storage systems4
San Luis Valley Solar Data (09/11/2010) Good Day [1]5San Luis Valley Solar Data (09/12/2010) Bad Day [1]
6Intermittent Wind Generation7
7Simplified System Model8Reference: [2]-[4]Sbase= 600 MVANetwork Electric SystemSteam Generator+Wind Generators+Energy Storage System (ESS)++Load -Gas GeneratorLoad (4-hr)Value (MWh)Winter~1500Summer~1640Input Data9Sbase = 600 MVA11th Jan 2011: 1 pm9th June 2011: 1 pm
Frequency - Winter10
~32% wind penetrationFrequency - Summer11
~29% wind penetrationPower Spectrum [1]12278 hours27.8 hours2.78 hours16.7 min100 sec10 sec2 sec
small magnitude:turbine acts aslow-pass filterTurbine upper limitEnergy StorageShort-termShort-term Storage Time Scale : 10 sec 3 hrsReferences[1] J. Apt, The spectrum of power from wind turbines, Journal of Power Sources, v.169, March 2007 [2] G. Lalor, A. Mullane, M. OMalley, "Frequency Control and Wind Turbine Technologies, IEEE Transactions on Power Systems, v. 20, no.4, November 2005[3] R. Doherty et al, An Assessment of the Impact of Wind Generation on System Frequency Control", IEEE Transactions on Power Systems, v.25, no.11, February 2010[4] P. Kundur, Power System Stability & Control, McGraw-Hill, 199413Matching Fossil Resources to the Net Loads In ColoradoGeneration Resource TypeRated Capacity [MW]Ramp Up [MW/hr]Ramp Down [MW/hr]Coal sub-total[i]2834322.58-630.27Gas sub-total77537.70-65.75Ramp per (MW/hr)/MW avg.NA.0998-.1926Total3609360.28-695.02Extrapolated Total7,884 MW786.82-1,518.30
Xcel PSCo Load Duration Curve and Net Load Duration CurvesMin Coal Generation15Case When Wind Energy Exceeds Capacity. Current Law Requires use of Wind EnergyThe wind energy may exceed the amount of gas fired energy that can be shut off and require the reduction of heat rate to coal fired plantsThis reduces electric power generation efficiency and increase emissions of SO2, NOx and CO2 for old plants It is expected to up to double the costs of maintenance. 16Example of Wind Event and Response
17Resulting Increase in SO2,NOx
18Emissions for Start Up, Ramping and Partial Loads IEEE Power systems Nov-Dec. 2013 19
Number of Ramps per Year20
Cost of Increasing Wind Energy Penetration
21Gas Cost Impact of wind penetration with and without storage on Xcels electric gridCost Impact of increasing wind penetration on Xcels electric grid
Lower Bound on Cycling Costs IEEE Power Systems Nov-DEC 201322
Increasing Cost with Penetration of Wind Power 123
23Approaches to Solving the Variability Issues.At low penetration grid spinning reserves. Gas fired generatorsStorage Batteries, super capacitors, fly wheels Pumped Hydroelectric systems, CAESDemand ResponseBiomass, geothermal24Energy Storage Systems
25Comparison of efficiency of several energy storage technologies
NREL report26Pumped Hydro Raccoon Mountain127
Pumped Hydro In Colorado128
Potential Locations and Capacity for Pumped Hydro in Colorado129
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Pumped Hydro Storage in Colorado
Wind Integration Study for Public Service of Colorado Addendum Detailed Analysis of 20% Wind Penetration http://www.xcelenergy.com/SiteCollectionDocuments/docs/CRPWindIntegrationStudy.pdf 30Snapshot of Pumped Storage Globally Rick Miller HDR/DTA
Pump Storage Units in Operation (MW) by Country/ContinentPumped Storage Projects Under Construction (MW)
Compressed Air Storage
33Compressed Air Energy Storage CAESQuestions of Interest
Where can we locate CAES.?Some Design ConsiderationsValue of Storage When is it Cost Effective?34Current and Planned CAES Systems 1. Huntorf Germany 1978 290 MW for 2 to 3 hours per cycle2. McIntosh, Alabama 110 MW ,19 million cubic feet and 26 hours per charge3. Others that have been under discussion for a long time A. Iowa Stored Energy Park B. Norton Ohio (2700 MW)4. Others?3536
Aerial view of Huntorf facility37
McIntosh facility plant roomCAES Characteristics 1. It is a hybrid system with energy stored in compressed air and need heat from another source as well. 2. Require 0.7 to 0.8 kWh off peak electrical energy and 4100 to 4500 Btu (1.2 -1.3 kWh) of natural gas for 1 kWh of dispatchable electricity 3. This compares with ~ 11,000 Btu/kWh for conventional gas fired turbine generators. 4. Efficiency of electrical energy out to electrical plus natural gas energy in ~ 50%3839CAES Characteristics Another way to calculate efficiency is comparing to the normal low efficiency of natural gas turbines with heat rate of 11000 Btu/kWh yielding 0.39 kWh of electricity and adding 0.75 kWh off peak electricity to get 1.14 kWhs to get 1 kWh of dispatchable electricityThis gives an efficiency of 88%
There are two types of CAES systems Underground CAES Above ground CAES 40Underground CEASPotential for large scale energy storage 100 to 300 MW for 10 20 hours.Effective in performing load management, peak shaving, regulation and ramping duty.Less capital cost compared to other large scale energy storage options.
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Main components of underground CAESChallenges associated with Underground CAESIdentification of suitable site for setting up a underground facility.Optimizing the compression process to reduce the compression work required.Thermal management efficiently extracting, storing and reusing the available heat of compression, thus improving the efficiency of the system.Understanding the effect of cyclic loading and unloading on the structural integrity of the underground cavern.
42Deep CAESDeep compressed air energy storage is an underground CAES facility where the cavern is formed at depths of >4000 ft. as against 1000-2000 ft. in case of conventional facilities. The main advantage of going deep are,Maximum permissible operating pressure of a cavern increases with depth. - A good approximation will be 0. 75 to 1.13 psi/ft. based on the local geology.Hence going deep helps store air at higher pressures in much smaller cavern volume, hence higher energy density.
The possibility of setting up a deep compressed air energy storage facility in Eastern Colorado is being currently investigated by Energy Storage Research group at CU, Boulder.
43Challenges associated with Deep CAESDeep CAES brings in additional challenges, which areUtilizing the high pressure compressed air effectively.Most of the off-the-self gas turbines operate in the range of 70-100 bars, hence it is necessary to design the system such that high pressures can be utilized.
Understanding the effect of high pressure & temperature on the cavern structure.
Identifying suitable equipment's / material to operate at high pressure .Potential for leakage through faults.
44Criteria for Site Selection451. Tight Cavern2. Adequate natural gas 3. Ability to withstand 600 to 1200psi for conventional & 2000 5000 psi for deep CAES.4. Proximity to Wind or Load to minimize transmission line losses. 5. Appropriate geology6. A report by Cohn et al. 1991 Applications of air saturation to integrated coal gasification/CAES power plants. ASME 91-JPGC-GT-2 says that this can be found in 85% of the US. Possible Geologies1. Abandoned Natural Gas fields.2. Old Mines3. Dome Aquifers4. Porous Sandstone4. Salt Domes 5. Bedded Salt46Why Salt Beds / Domes?Salt beds are more desirable for setting up new Caverns because of the following reasons,Easy to be solution mined Salt has good Elasto-plastic properties resulting in minimal risk of air leakageSalt deposits are widespread in many of the subsurface basins of the continental US, including western states (Colorado, West Texas, Utah, North Dakota, Kansas)
47Salt Formations 48
Potential CAES Sites 49
Potential CAES In Colorado50
Gas Well in The Denver Julesburg Basin 51
Neutron Porosity Log52
Salt Beds In Pink53
Salt Beds In Eastern Colorado 1. Salt beds from 4100 ft to 6,800 ft.2.Thickness from 3 to 292 ft. 3. Required Operating pressures in the range of 4000 to 7000 psi. 6 At about 6,000 psi we need about 14,400 cubic meters per gigawatt hour energy storage or a cavern of about 30 x22 x 22 meters 54Need for thermal managementWhen air is compressed - up to 85% of the energy supplied is lost in the from of heat.
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Even with isothermal compression 50% of the energy may be lost as heatStoring and re-using the heat of compression would result in increasing the overall efficiency of the CAES system and result in reduced or no fuel consumption.
Figure showing the fraction of work stored in compressed air Vs. the pressure. Rest dissipated as heat.Polytrophic compressionIsothermal CAES56Another approach to keep the temperature constant during compression is to slow down the pumping process (As it results in efficient heat dissipation thus constant temperature).Such a system can be used for small scale applications.
Isothermal CAES developed by SustainXThe SustainX system operates at 0 to 3000 Psi and provides 1 MW for 4 hours at an expected efficiency of 70%. The SustainX system is a hydro Pneumatic system, in which the electrical energy is used to run a hydraulic pump, this hydraulic pressure is then used to operate a double acting piston cylinder assembly which then compresses the air. Thus the compression process can be controlled and can be achieved at a slower rate.56Recent developments in AA - CAES57
RWE group, Germany in collaboration with GE are developing an AA-CAES project. (Started 2010)They propose no fuel operation with a target efficiency of 70%
Findings:Feasibility study has shown that such high efficiencies can be achieved by system optimization and suitable equipment development.
Challenges:R&D is being carried out to develop Turbomachinary & Thermal energy storage to achieve the above goals.
The aim of the programme is to advance adiabatic compressed air energy storage technology in preparation for a first plant to be tested in a subsequent demonstration project. The preferred site for this first demonstration plant is Stassfurt (Saxony-Anhalt) that is located in a region marked by wind energy use. The ADELE-Stassfurt project will have a storage capacity of 360 megawatt hours and an electric output of 90 megawatts. This enables ADELE-Stassfurt to provide substitute capacity at extremely short notice and replace up to 50 wind turbines of the type used in the region for a period of four hours. Altogether, the parties involved in the project are making available 12 million for the ADELE development phase by 2013. They are supported by Germanys Ministry of Economics and Technology (BMWi) with funds from the COORETEC programme. ADELE will help provide peak-load electricity from renewables completely without CO2emissions.57Storing & Re-use of compression heatHeat of compression can be stored in two ways With the help of thermal energy storage facility By storing the heat in compressed air itself
There are two options for utilizing the stored energyUsing the stored heat + Fuel for preheating the airOnly utilizing the stored heat (No Fuel) also called as Advanced Adiabatic CAES (AA-CAES).
58Thermal Time ConstantsThermal time constants vary with the surface to volume ratio. For a Sphere For a Cylinder
For a cube
For a rectangle59
(Source: Geyer 1991)
60Physical Properties of Sensible Storage MaterialsMajor Cavern Design parametersCavern geometry & volumeDepth of the cavern as the overburden pressure increases with depthCavern Minimum operating pressure as inside pressure of the cavern acts as a static lining to the cavern contourCavern maximum operating pressure must be fixed to avoid gas infiltration and cracking of the surrounding rock massCavern operation pattern Distance between adjoining caverns61Cavern operating pressuresOperating pressure of the cavern depends on the,Depth of the cavernThe in-situ stresses in the surrounding rock formation.The maximum operating pressure of the above ground equipment.
62Effect of cyclic loading on cavernIncrease in cavern inside pressure causes increase in deviatoric stresses, this in turn results in increase in creep rate. Its has been found by laboratory experiments that the overall creep rate decreases in case of cyclic loading, thus resulting in reduced convergence good for CAES. But the stresses in the rock mass increases.Charging & discharging of cavern is associated with rise and fall in temperature inside the cavern as well as the rock surrounding it. Heating of rock salt creates thermal induced compressive stresses, cooling of rock salt creates thermal induced tensile stresses.
*Results of experiments conducted by University of Technology, Clausthal-Zellerfeld, Germany
63Deviatoric stress is the difference between the gas pressure and the in-situ stress on the surrounding salt. 63Effect of cyclic loading on cavern64
Transient effect of cyclic stresses on the salt cavern (cycle period 5 days) The graph shows the reducing creep rate & increase in stress with time.*Results of experiments conducted by University of Technology, Clausthal-Zellerfeld, Germany
Effect of cyclic loading on Cavern65
Change in contours of the Huntorf Caverns between 1984 & 2001Survey of the Huntorf cavern contour conducted in 1984 & 2001 show negligible convergence of the cavern in spite of continuous cyclic operation.
Visualization of thermally induced cracks in salt rock
Further work needed:Understanding the thermo-mechanical effects (convergence & creep) on surround rock at high pressures & temperature.Effect of different charging and discharging periods / operation patternsEffect of having a deep cavern at atmospheric pressure for maintenance work.
66Effect of cyclic loading on CavernSystem Integration67One of the suitable configurations to utilize the maximum available pressure
Economics 1. Costs A. A little more than conventional gas fired generators at $4oo to $500/kWB. CAES estimates at $600 to $700/kW (Note these numbers could be low depending on the site etc)C. Low Operating Costs2. ValueA. Smooth out wind fluctuationsB. Match to transmission line limits.C. Match to loads increasing capacity factor. 68Economics2. ValueD. Absorb Energy when the wind power exceeds transmission or load. This is in contrast to gas fired generators E. Arbitrage , buy wind or other energy low and sell high. F. Ancillary services , frequency control, black start etc.G. Reduced natural gas consumption by approximately two thirds. 69Economics Factors effecting CAES capital cost CAES site selection Depth of Cavern Local geology Proximity to transmission network Availability of Natural gas Presence of Thermal energy storage.Factors effecting CAES Operating costCost of off peak energy and/or Wind energy generation cost.Natural gas requirement based on TES availability
70Levelized Cost of Electricity CAES Options71
LCOE as a function of depth72
Chart18811453.422023549.2513618844.51941936569.639907.1
MW's
Sheet6Sum of MW9 regionsTotalAsia w/o China & India36569.6China19419Europe39907.1India5136Latin America1453.4Middle East & Africa3549.2North America18844.5Oceania881Russia & CIS2202(blank)Grand Total127961.8RegionMW'sOceania881Latin America1,453Russia & CIS2,202Middle East & Africa3,549India5,136North America18,845China19,419Asia w/o China & India36,570Europe39,907
Sheet6000000000
MW's
Chart1404505298008528561368162817302200
MW'S
pivot under construction9 regions(All)Count of MWCountryTotalAUSTRIA3CHINA8JAPAN5KOREA SOUTH2Portugal6RUSSIA4SOUTH AFRICA4SPAIN4SWITZERLAND8(blank)Grand Total44COUNTRYMW'SUNITED STATES40PORTUGAL450AUSTRIA529KOREA SOUTH800SPAIN852RUSSIA856SOUTH AFRICA1368SWITZERLAND1628JAPAN1730CHINA2200
pivot under construction404505298008528561368162817302200
MW'S
