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Energy Storage for Concentrating Solar Power Plants

Solar Thermal Energy Storage Technologies Doerte Laing, German Aerospace Center (DLR) ENERGY FORUM, 10,000 Solar GIGAWATTS Hannover, 23. April 2008. CONCENTRATING SOLAR COLLECTOR. KONZENTRIERENDER. SONNENKOLLEKTOR. ENERGIE. ENERGY. -. -. STORAGE. SPEICHER. Solar. Solar. -. (optional).

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Energy Storage for Concentrating Solar Power Plants

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  1. Solar Thermal Energy Storage TechnologiesDoerte Laing, German Aerospace Center (DLR)ENERGY FORUM, 10,000 Solar GIGAWATTSHannover, 23. April 2008

  2. CONCENTRATING SOLAR COLLECTOR KONZENTRIERENDER SONNENKOLLEKTOR ENERGIE ENERGY - - STORAGE SPEICHER Solar Solar - (optional) (optional) Fossil heat fuel Electricity W Ä RMEKRAFT - POWER BLOCK MASCHINE Heat Energy Storage for Concentrating Solar Power Plants Higher solar annual contribution Reduction of part-load operation Power management Buffer storage Energy storage necessary for successful market implementation of CSP technology

  3. Thermal Energy StorageChallenges Highly specific design specifications regarding: primary HTF - pressure - temperature - power level - capacity Storagesystem ONE single storage technology will not meet the unique requirements of different solar power plants

  4. Storage concepts for parabolic trough power plants Classification Heat transfer fluid as storage media Two tank oil storage Direct active thermal energy storage Steam Accumulator Dual medium storage system liquid Molten salt sensible heat storage Passive thermal energy storage solid Solid media sensible heat storage phase change Latent heat storage

  5. Thermal Energy Storage for CSP Plants Status und Development • Commercially available storage systems • Steam Accumulator • 2-Tank sensible molten salt storage based on nitrate salts • Alternative materials and concepts tested in lab and pilot scale • Solid medium sensible heat storage - concrete storage • Latent heat - PCM storage • Combined storage system (concrete/PCM) for water/steam fluid • Improved molten salt storage concepts • Solid media storage for Solar Tower with Air Receiver (e.g. natural rocks, checker bricks, sand) • Future focus for CSP • Higher plant efficiency => Increase process temperature • New fluids: steam, molten salt, gas/air

  6. Steam AccumulatorsStorage of sensible heat in pressurized liquid water Charging process:raising temperature inliquid water volume by condensing steam Discharging process:generation of steamby lowering pressure in saturated liquid water volume →Buffer storage for peak power →Inefficient and economically not attractive for high pressures and capacities

  7. Steam AccumulatorsPS10 Saturated steam at 250°C50 min storage operation at 50% load

  8. Steam AccumulatorsPS10

  9. Steam AccumulatorsPS10

  10. Molten Salt Storage - Solar Two • Storage capacity (3h) • 1400 t of nitrate salts (60% NaNO3 + 40% KNO3) • 2 tanks: 12 m Ø, 8 m high

  11. Syn. Oil H2O NaNO3-KNO3 Molten salt storage Conventional steam turbine Collector field Molten Salt Storage – Andasol 1

  12. 14 m 386 °C 292 °C Ø 38,5 m Molten Salt Storage – Andasol 1 Salt inventory 28.500 t Tank volume 14.000 m³ 6 HTF/salt heat exchangers • Storage capacity 1010 MWh (7.7h) • Nitrate salts (60% NaNO3 + 40% KNO3)

  13. Molten Salt Storage – Andasol 1 Source: ACS Cobra

  14. Solid media concrete storage • Dual medium indirect storage system with regenerative heat transfer • Preferred for single phase HTF up to 400/500 °C • Modular and scalable design from 500 kWh to 1000 MWh • Economic and reliable TES • Cost target < 20 € / kWh TES capacity • Flexible to large no. of sites and construction materials

  15. Solid media concrete storage – Current Status • 2 year operation of 2 modules350 kWh castable ceramic350 kWh concrete • Second generation concrete400 kWh storage moduledeveloped with • Current investment cost~ 30 €/kWh(large scale, 6 h cycles) • Concrete storage is ready for scale-up and demonstration • System integration and operation strategy is an important issue

  16. 134 mm Solid media concrete storage – Storage Design Basic storage module 18 m 4 m 2,6 m

  17. 25 m 50 m Solid media concrete storage – Storage DesignSet-up of storage units Storage Package

  18. Solid media concrete storage – Storage DesignPiping

  19. Solid media concrete storage Integration into power plant 50.000 m³ Concrete Storage Material  6 h – Storage for 50 MW-Power Plant

  20. Significant advantage of PCM technology in steam production due to constant temperature Phase Change StorageWhy using Phase Change Material (PCM) ? Working fluid water/steam: => Evaporation phase (T=const) Phase change storage medium=> Melting phase (T=const)

  21. Phase Change StorageSelection of Phase Change Materials For industrial process heat For solar power generation

  22. Finned Tube Designeffective Lamda >10 W/(mK) Approaches to realize PCM with superior thermal conductivity Heat transfer coefficient is dominated by the thermal conductivity of the solid PCM → Low thermal conductivity is bottleneck for PCM

  23. On-sun demonstration of a 200 kWh PCM storage Dimensions: 5 x 0,6 x 0,5 m3 PCM: 2 tons nitrate salt - 120 kg graphite plates Maximum pressure: 40 bar Charging/discharging power 100 kW Thermal capacity 200 kWh Estimated investment cost: 45 €/kWh th

  24. C B D A Combined Concrete / PCM Storage for direct steam generation in parabolic troughs from solar field evaporation/ condensation superheating to solar field preheating concrete storage module from power block concrete storage module PCM storage module to power block A feed water inlet / outlet B liquid water C saturated steam D live steam inlet / outlet

  25. Conclusions • Energy storage is a key issue for CSP • Steam accumulators only economic as buffer storage • Molten salt technology is available, further improvements for cost reduction needed • Concrete storage technology is attractive alternative – demonstration in pilot scale needed • PCM storage technology is the most promising technology for DSG plants • Continuous research and development effort is needed especially for higher process temperatures (> 400°C) and for further cost reduction

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