1. Compressed Air Energy Storage System with Integrated Low-Grade Heat Capture Dr. Bruno Cárdenas, Prof. Seamus D. Garvey, Mr. Michael C. Simpson, Mr. Bharath Kantharaj, Dr. Andrew J. Pimm, Mr. James E. Garvey London, June 08, 2016 Presented at the UK Thermal Energy Storage Workshop 8-9 June 2016, Imperial College, London

2. Structure London, June 08, 20162 Part 1: Generation-integrated energy storage (GIES) Part 2: Compressed air energy storage (CAES) with increased exergy capacity Part 3: A CAES system with integrated solar capture

3. Structure London, June 08, 20163 Part 1: Generation-integrated energy storage (GIES) Part 2: Compressed air energy storage (CAES) with increased exergy capacity Part 3: A CAES system with integrated solar capture

4. Common examples of GIES : Hydroelectric power Concentrated Solar Power Biomass Generation-Integrated Energy Storage (GIES) is a subset of generation technologies that store energy before conversion to electricity. Integrating storage with generation London, June 08, 20164 Advantages: Less number of transformations = less energy losses Capital cost savings from power-conversion equipment.

5. Natural hydro as GIES London, June 08, 20165 Run of the river Pure generation Pure storage Pumped hydro Generation integrated storage Conventional hydroelectric Primary energy Storable form Electricity Passive transport, no transformation Passive transport, conversion in turbine

6. Concentrating solar power London, June 08, 20166 Natural fit for integrated thermal storage. Typically used as an alternative to PV, rather than complementary.

7. Structure London, June 08, 20167 Part 1: Generation-integrated energy storage (GIES) Part 2: Compressed air energy storage (CAES) with increased exergy capacity Part 3: A CAES system with integrated solar capture

8. CAES Variants London, June 08, 20168 Heater Compressed Air Store Ambient Air W W Fuel Compressed Air Store Ambient Air W W TES Heat of compression lost Reheat using natural gas Diabatic CAESAdiabatic CAES Heat of compression stored and re-used during discharge. Isothermal CAES Compression and expansion take place at near ambient temperature, with environment as heat store.

9. Dominant Costs London, June 08, 20169 2012 Black & Veatch study of 262 MW plant with 15 hours of storage predicted capital cost of $900/kW Cavern cost accounts for 40%. High fixed and low marginal costs of salt cavern mean this depends only weakly on capacity. For small-scale CAES, the cost of pressure vessels scales with gauge pressure x volume CAES plants are expected to be very competitive for long-duration storage, but further cost reductions would encourage investment. Cavern 7% 30% 14% 6% 3%

10. Use of pressure containment London, June 08, 201610 Exergy in isochoric store with pressure ratio, Exergy in isobaric store with press. ratio, Or, if the HP air is displaced naturally by hydrostatic head (removes energy input for pumping) e.g.

11. Compressing and cooling air London, June 08, 201611 P 1, T 2 1J of work on pre-heated air 1J of heat between T 2 and T 3 Exergy split between air and high temperature heat P 0, T 0 P 1, T 1 1J of work on ambient air 1J of heat between T 0 and T 1 All exergy in pressurised air (if T 0 ≈ T 1 ) Compression Cooling Result P 0, T 0 P 0, T 2 P 1, T 3

12. Use of preheat London, June 08, 201612 1 1a 2a 3 3a 1 1a 2a 3 2 3a

13. Charging London, June 08, 201613 1 1a 2a 3 3a 1 1a 2a 3 2 3a

14. Discharging London, June 08, 201614 1 1a 2a 3 3a 1 1a 2a 3 2 3a

15. Pressurized air vs thermal storage London, June 08, 201615 For a given pressure store size, pre-heating air increases the total exergy stored significantly. Storage pressure80 bar Max temperature (after compression) 1000K Modelled as reversible B stored /B air Isothermal CAES1.00 Adiabatic CAES2.08 Adiabatic CAES with pre-heat to 660K 3.01 Exergy split for adiabatic CAES with pre-heat

16. Structure London, June 08, 201616 Part 1: Generation-integrated energy storage (GIES) Part 2: Compressed air energy storage (CAES) with increased exergy capacity Part 3: A CAES system with integrated solar capture

17. CAES system with Low-Grade Heat Capture London, June 08, 201617 Thermal stores Pressure store Solar thermal capture Single stage expansion Three stage compression with intercooling Water tank Heat pump

18. Charging phase London, June 08, 201618 Exergy transferred to high pressure air and top thermal store.

19. Solar thermal charging London, June 08, 201619 Exergy transferred to lower thermal stores.

20. Discharging phase London, June 08, 201620 Fluid flow Heat flow Exergy extracted from high pressure air and all thermal stores.

21. Example system with irreversibilities London, June 08, 201621 1 2 3 4 5 6 7 8 Air charge Power (charge)100MW Power (discharge)250MW Storage duration (at 100MW)12 hours Storage pressure80 bar Cavern size55,000m 3 Mass flow of air (charge)95 kg/s Exergy into pressurised air430MWh Exergy into high temp. store720MWh Solar input energy at 350°C1030MWh Ground area of solar capture≈ 700m x 700m

22. Modelling discharge process London, June 08, 201622 Work ongoing on discharge modelling. Analysis covering: Raising of steam Air-steam mixing Humid air turbine Heat pump Exhaust heat recuperation Fluid flow Heat flow

23. Applications London, June 08, 201623 Most relevant where there is strong solar resource and low-cost pressure storage, such as salt caverns or deep water. Where solar resource is not available, waste gases may be used as a least-worst solution. Candidate locations include: Chile Mediterranean countries, esp. Spain Gulf of Mexico India

24. Concluding Remarks / Future Work London, June 08, 201624 Preliminary modelling indicates greatly increased exergy storage for a given pressure store. A variant on CAES incorporating pre-heating and solar thermal capture has been proposed. Needed: Thermodynamic modelling of discharge cycle to assess exergy losses and Techno-economic assessment of costs and value of generation and storage service provided.

25. Acknowledgements London, June 08, 201625 Thanks to EPSRC for supporting this work under: NexGen-TEST (EP/L014211/1) IMAGES (EP/K002228/1) RESTLESS (EP/N001893/1) Thanks to colleagues also active in compressed air and thermal energy storage at: Leeds Cambridge Birmingham Loughborough Warwick Chinese Academy of Sciences

26. References London, June 08, 201626 Garvey SD et al., “On generation-integrated energy storage,” Energy Policy, vol. 86, pp.544-551, 2015. Zunft S, “Adiabatic CAES: The ADELE-ING project,” presented at SCCER Heat & Electricity Storage Symposium, Villigen, Switzerland, 2015. Haughey C, “Larne CAES: a project update,” Gaelectric, Belfast, Ireland, article, 2015. Black & Veatch Holding Company, “Cost and Performance data for Power Generation Technologies,” 2012. White AJ, McTigue JD, Markides CN, “Analysis and optimisation of packed-bed thermal reservoirs for electricity storage applications,” to be published. Garvey SD, “Two Novel Configurations for Compressed Air Energy Storage Exploiting High-Grade Thermal Energy Storage,” presented at UK-China Thermal Energy Storage Forum, Beijing, China, 2015. Solar Millennium, “The parabolic trough power plants Andasol 1 to 3,” Erlangen, Germany, report, 2008. Jorgenson J et al., “Estimating the Performance and Economic Value of Multiple Concentrating Solar Power Technologies in a Production Cost Model,” NREL, Denver, Colorado, Report NREL/TP-6A20- 58645, 2013. RWE, “Adele – Adiabatic compressed-air energy storage for electricity supply,” Essen/Cologne, Germany, report, 2010. Young-Min, K et al., “Potential and Evolution of Compressed Air Energy Storage: Energy and Exergy Analyses,” Entropy, vol. 14, no. 8, pp.1501-1521, 2012.