Bill Gould, CTO at SolarReserve, presented at the GW Solar Institute Symposium on April 19, 2010. For more information visit: solar.gwu.edu/Symposium.html

1. Thermal Energy Storage Bill Gould George Washington University Chief Technology Officer April 2010

2. INTERMITTANCY AND RENEWABLES Wind Generation Varies Day-to-Day : Hour-to-Hour Tehachapi Wind Generation

3. WIND ENERGY GENERATION PROFILE SCE Average Load July MW Wind Generation July Wind Generation Out of Phase With Demand

4. Just a Pretty Little Cloud

5. Future Storage Concepts Being Studied New Lower Freezing Point Heat Transfer Fluids Phase Change Materials, Thermo-chemical Storage, Sand Sifter, Nano Particles and Nano Tubes Graphite or Concrete Monoliths

7. Concrete can be inexpensive, but there is concern about concrete separating from the HTF tube after many thermal cycles. Tests underway at DLR look promising.

8. Cost is still a question for other solid media.

9. But steam turbines work best with constant high temperature steam.Concrete Block Pipe Filled w. Solid Media

10. Two Tanks Capture More Energy Than a Single Tank 1000 Watts / M2 200 Watts / M2 5:1 TURNDOWN CAPABILITY Receiver Receiver Low Insolation Operation Normal Operation 288 to 566oC 566oC Hot Tank 566oC Hot Tank 566oC Cold Tank 288oc Cold Tank 288oc Single Tank Systems (Steam, Ceramic & Concrete) Cannot Capture Energy at Low Temperatures w/o Degrading the Hot Side Inventory.

11. Deployable Technologies Steam in Pressure Vessels Compressed Air – in Tanks or in underground caverns. Pumped Storage – using Water Concrete Monoliths. Other Solids: Ceramics, Alumina, Iron Oxides, etc. Molten Nitrate Salts: Single-Tank Thermocline Two-Tank System

13. Requires an ASME stamped pressure vessel.

14. Cannot support large scale:

15. Utility dispatch and curtail,

16. Dispatch over night or through a long storm,

17. Load Multiplying- for peaker duty,

18. Cannot efficiently collect energy at various temperatures on hazy days or near sunset.ASME PRESSURE VESSEL Primarily useful to provide grid stability through short cloud transients.

19. Pumped Storage and Pressurized Caverns Neither feature need be adjacent to the solar plant – as long as there is a transmission line to the geologic feature. Pumped Storage Requires a mountain and two reservoirs. Concepts and costs are well understood. Underground Salt Cavern requires the right geological features, plus development. Underground Cavern Both Pumped Hydro and Compressed Air in Caverns work. Both require extensive infrastructure development!

21. Work best with tall, narrow cylinders (to keep the interface zone from growing to fill the entire volume.

22. Tall and narrow costs more than than short and fat.

23. Does not scale to commercial sized plants. Which might use 50 to 75 million pounds of salt.HOT INTERFACE COLD HOT COLD Thermoclines’ promised cost advantage does not scale.

24. Power Towers Power Towers Grew Out of Solar One & Solar Two 12 Confidential and Proprietary

25. How Does It Work? POWER BLOCK HP TURBINE IP/LP TURBINE STEAM TURBINE GENERATOR MOLTEN SALT SYSTEM GENERATOR CONDENSER RECEIVER COLLECTOR FIELD Reheat Steam HP Steam Receiver Tower Hot Salt Reheater Superheater MOLTEN SALT LOOP Steam Gen./Evaporator Condensate Tank 565°C FeedwaterPreheaters Cold Salt HELIOSTATS STEAM GENERATION SYSTEM 288°C THERMAL STORAGE SYSTEM

26. 14 UTC Proprietary molten salt thermal storageSeparates thermal energy collection from electric power production Thermal Energy Stored in Molten Salt Option 1 High Power Peaker Plant Power (Mwe) Energy (Mwt-hr) Option 2 Constant Power Base-load Plant Sunlight Sunlight Noon Midnight Midnight Noon

27. 15 Confidential and Proprietary Client Selects Power Usage 15

29. Exceeded Performance Targets

30. Demonstrated ability to produce power 24 hours/day16 Confidential and Proprietary “…. The 10-megawatt Solar Two power tower pilot plant near Barstow, California, successfully completed operations in April 1999, having met essentially all of its objectives. It demonstrated the ability to collect and store solar energy efficiently and to generate electricity when needed by the utility and its customers. Based on the success of Solar Two, U.S. industry is actively planning the first commercial implementation of this technology….” SunLabSnapShot March 2000

31. S0lar One & Solar Two Collector Fields 17 Confidential and Proprietary

32. Receiver is the Heart of the System 18 Confidential and Proprietary

33. SolarReserve’s Technology Partner 19 Confidential and Proprietary UTC $59B Revenue Carrier Sikorsky UTC Fire & Security Otis Hamilton Sundstrand UTC Power Research Center Pratt & Whitney Rocketdyne 3,500 Employees 1,300 Technical Degrees HS Rocketdyne PW Rocketdyne

35. Hundreds of regeneratively cooled tubes.

36. Precision shapes, exotic alloys.

37. Instantaneous, severe temperature gradients20 Confidential and Proprietary 3,316˚C Rocket Flame -204˚C Hydrogen Coolant 650oC Tube Surface Temperature 288oC Cold Salt Temperature

38. Molten Salt Loop – Receiver System 21 Confidential and Proprietary Stress Analysis of Tube-to-Header Joint Upper Header and Tube Installation ANSYS Structural Analysis of Tube Clip Aerospace “mission critical” quality thermal, fluid flow and structural analyses. Larger system actually operates at lower risk conditions

39. Upper Header and Tube Installation 22 Confidential and Proprietary

40. Upper Header and Tube Installation 23 Confidential and Proprietary

41. Salt Piping 24 Confidential and Proprietary All Salt Piping is Enclosed and Sloped Downward

43. 30-year design life

44. Either tank safely able to hold total salt inventory

45. Tank heel volumes minimized

46. 99% thermal storage efficiencySteam drum Reheater Evaporators Superheaters Preheater Cold Tank Hot Tank

47. Steam Generator Building Cold Salt Tank Hot Salt Tank Control Building Receiver Tower Plant General Arrangement Turbine Generator Building Receiver Assembly Area Switchyard Air Cooled Condenser

48. Just a Pretty Little Cloud

50. Solar One – 1979 – 1984 (Direct Steam)

51. Solar Two – 1994-1999 (Molten Salt)

52. Which fluid was best? Why?Direct Steam SALT Direct Steam

53. The Advantages of Thermal Storage Solar PV Varies Minute-to-Minute: Second-to-Second Steam Drum Limits

54. The Hot Tank is An Energy Integrator The hot tank sums instantaneous energy flows. The turbine sees the integral of these flows. Collection may be interrupted by cloud passage – but not generation. So cloud passage never interrupts generation during peak periods, it only brings forward the shut down late at night.

55. Typical Solar Thermal Trough System Solar field Steam Cycle Heated collecting main pipe Steam turbine Solar warmer Electricity Generator Natural Gas Boiler Condenser Eurothough Collectors Solar steam generator Degasification Solar pre-warmer Low pressure warmer Water circuit pump Solar warmer Expansion Tank Cooled collecting main pipe Thermal fluid pump Many solar plants need a gas boiler to maintain temperature on weak days.

57. At What Temperature Can You Store Heat? . Stored Heat =∑ mCpΔT Salt Therminol Stored Heat is Proportional to ΔT Large / Smaller ΔT ≈ 278°C/90°C Low Temperature Storage Requires ≈ 3X mass 566°C ~378°C 288°C 288°C Low Temperature Storage ~ 3X Cost per MWt

59. Warehouse, and spare parts inventory,

60. Administration building,

61. Operation and maintenance staff

62. SwitchyardModular - Multi-Plant Site

63. What is the Optimum Receiver Size? There Are Strong Economies of Scale! Results of Thousands of Monte Carlo Analyses Evaluating Plant Cost versus Receiver Size (MWt) NORMALZIDED COST($/MW) 0 100 200 300 400 500 600 700 800 THERMAL POWER (MW) Relatively flat curve between 500 and 650 MWt receiver sizes

64. What is the Optimum Receiver Size? There Are Strong Economies of Scale! Multiple Towers of an Inefficient Size Only Multiply the Inefficiencies NORMALZIDED COST($/MW) 0 100 200 300 400 500 600 700 800 THERMAL POWER (MW) Relatively flat curve between 500 and 650 MWt receiver sizes

65. Ten Towers Generate One Gigawatt (24x7) 1GW : 24/7 Solar Park Layout 12 Place picture of ten tower station here. Control Room And Common Facilities 2500 meters Each plant has standalone Turbine and Steam Generator 1GW : 24/7 Solar Park Layout 12 Control Room And Common Facilities 2500 meters Each plant has standalone Turbine and Steam Generator

67. Clothing not ignited

68. Paper in Trash Can Not Even SingedME Trash 38 Confidential and Proprietary

70. Clothing not ignited

72. No damage to paint

73. No burning, melting or chemical interaction with soft foam rubber gaskets or windshield wipersTrash

75. Break up the frozen puddle with shovels

76. Load chunks of salt and sand into barrels

77. Haul barrels awaySalt from a small flange leak is recoverable. Operators simply break off the frozen stalactite and throw it back in the tank. Molten Salt Tank Frozen Salt Puddle Salt freezes within the top centimeter of soil, Therminol stays liquid and seeps up to 5’ meters into the sand.

79. Pump salt through a shower head at the top

80. Salt cools, solidifies and “prills” as it falls

81. Laborers load the prills into shipping bags