Gould - Thermal Energy Storage


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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

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Gould - Thermal Energy Storage

  1. 1. Thermal Energy Storage<br />Bill Gould<br />George Washington University<br />Chief Technology Officer<br />April 2010<br />
  2. 2. INTERMITTANCY AND RENEWABLES<br />Wind Generation Varies Day-to-Day : Hour-to-Hour<br />Tehachapi Wind Generation<br />
  3. 3. WIND ENERGY GENERATION PROFILE<br />SCE Average Load July<br />MW<br />Wind Generation July<br />Wind Generation Out of Phase With Demand<br />
  4. 4. Just a Pretty Little Cloud<br />
  5. 5. Future Storage Concepts Being Studied<br />New Lower Freezing Point Heat Transfer Fluids<br />Phase Change Materials, <br />Thermo-chemical Storage, <br />Sand Sifter,<br />Nano Particles and Nano Tubes<br />Graphite or Concrete Monoliths<br />
  6. 6. Solid Media: Concrete, Ceramic, Alumina Manganese Oxide, Iron, etc.<br /><ul><li> Concrete blocks and Solid Media containers might be paired with heated air, CO2 or liquid heat transfer fluids.
  7. 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. 8. Cost is still a question for other solid media.
  9. 9. But steam turbines work best with constant high temperature steam.</li></ul>Concrete Block<br />Pipe Filled w. Solid Media<br />
  10. 10. Two Tanks Capture More Energy Than a Single Tank <br />1000 Watts / M2<br />200 Watts / M2<br />5:1 TURNDOWN CAPABILITY<br />Receiver<br />Receiver<br />Low Insolation Operation<br />Normal Operation<br />288 to 566oC<br />566oC<br />Hot Tank<br /> 566oC<br />Hot Tank<br />566oC<br />Cold Tank<br />288oc<br />Cold Tank<br />288oc<br />Single Tank Systems (Steam, Ceramic & Concrete) Cannot Capture Energy at Low Temperatures w/o Degrading the Hot Side Inventory.<br />
  11. 11. Deployable Technologies <br />Steam in Pressure Vessels <br />Compressed Air – in Tanks or in underground caverns.<br />Pumped Storage – using Water<br />Concrete Monoliths.<br />Other Solids: Ceramics, Alumina, Iron Oxides, etc. <br />Molten Nitrate Salts:<br />Single-Tank Thermocline <br />Two-Tank System<br />
  12. 12. Storing Steam in Large Pressure Vessels<br /><ul><li>Should work well through short cloud transients.
  13. 13. Requires an ASME stamped pressure vessel.
  14. 14. Cannot support large scale:
  15. 15. Utility dispatch and curtail,
  16. 16. Dispatch over night or through a long storm,
  17. 17. Load Multiplying- for peaker duty,
  18. 18. Cannot efficiently collect energy at various temperatures on hazy days or near sunset.</li></ul>ASME PRESSURE VESSEL<br />Primarily useful to provide grid stability through short cloud transients.<br />
  19. 19. Pumped Storage and Pressurized Caverns<br />Neither feature need be adjacent to the solar plant – as long as there is a transmission line to the geologic feature.<br />Pumped Storage<br />Requires a mountain and two reservoirs. Concepts and costs are well understood.<br />Underground Salt Cavern requires the right geological features, plus development.<br />Underground Cavern<br />Both Pumped Hydro and Compressed Air in Caverns work. <br />Both require extensive infrastructure development!<br />
  20. 20. Thermocline Thermal Storage Systems<br /><ul><li>Thermoclines promise savings (one tank instead of two).
  21. 21. Work best with tall, narrow cylinders (to keep the interface zone from growing to fill the entire volume.
  22. 22. Tall and narrow costs more than than short and fat.
  23. 23. Does not scale to commercial sized plants. Which might use 50 to 75 million pounds of salt.</li></ul>HOT<br />INTERFACE<br />COLD<br />HOT<br />COLD<br />Thermoclines’ promised cost advantage does not scale. <br />
  24. 24. Power Towers<br />Power Towers Grew Out of Solar One & Solar Two<br />12<br />Confidential and Proprietary<br />
  25. 25. How Does It Work?<br />POWER BLOCK<br />HP<br />TURBINE<br />IP/LP<br />TURBINE<br />STEAM TURBINE GENERATOR<br />MOLTEN SALT SYSTEM<br />GENERATOR<br />CONDENSER<br />RECEIVER<br />COLLECTOR FIELD<br />Reheat <br />Steam<br />HP<br />Steam<br />Receiver<br />Tower<br />Hot Salt<br />Reheater<br />Superheater<br />MOLTEN SALT LOOP<br />Steam Gen./Evaporator<br />Condensate Tank<br />565°C<br />FeedwaterPreheaters<br />Cold Salt<br />HELIOSTATS<br />STEAM GENERATION SYSTEM<br />288°C<br />THERMAL STORAGE SYSTEM<br />
  26. 26. 14<br />UTC Proprietary<br />molten salt thermal storageSeparates thermal energy collection from electric power production<br />Thermal Energy<br />Stored in<br />Molten Salt<br />Option 1 <br />High Power<br />Peaker Plant<br />Power (Mwe)<br />Energy (Mwt-hr)<br />Option 2 Constant Power<br />Base-load Plant <br />Sunlight<br />Sunlight<br />Noon<br />Midnight<br />Midnight<br />Noon<br />
  27. 27. 15<br />Confidential and Proprietary<br />Client Selects Power Usage<br />15<br />
  28. 28. Technology Validated at Solar Two<br /><ul><li>Technology Demonstrated at “Solar Two”
  29. 29. Exceeded Performance Targets
  30. 30. Demonstrated ability to produce power 24 hours/day</li></ul>16<br />Confidential and Proprietary<br />“…. 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….”<br />SunLabSnapShot March 2000<br />
  31. 31. S0lar One & Solar Two Collector Fields<br />17<br />Confidential and Proprietary<br />
  32. 32. Receiver is the Heart of the System<br />18<br />Confidential and Proprietary<br />
  33. 33. SolarReserve’s Technology Partner <br />19<br />Confidential and Proprietary<br />UTC<br />$59B Revenue <br />Carrier<br />Sikorsky<br />UTC Fire & Security<br />Otis<br />Hamilton Sundstrand<br />UTC Power<br />Research Center<br />Pratt & Whitney<br />Rocketdyne<br />3,500 Employees<br />1,300 Technical Degrees<br />HS Rocketdyne<br />PW Rocketdyne<br />
  34. 34. Receiver: High-Tech Portion of Plant<br />Technology Leverage<br /><ul><li>Engineered to withstand extreme thermal cycles.
  35. 35. Hundreds of regeneratively cooled tubes.
  36. 36. Precision shapes, exotic alloys.
  37. 37. Instantaneous, severe temperature gradients</li></ul>20<br />Confidential and Proprietary<br />3,316˚C Rocket Flame<br />-204˚C Hydrogen Coolant<br />650oC Tube Surface Temperature<br />288oC Cold Salt Temperature<br />
  38. 38. Molten Salt Loop – Receiver System<br />21<br />Confidential and Proprietary<br />Stress Analysis of <br />Tube-to-Header Joint<br />Upper Header<br />and<br />Tube Installation<br />ANSYS Structural Analysis of Tube Clip<br />Aerospace “mission critical” quality thermal, fluid flow and structural analyses.<br />Larger system actually operates at lower risk conditions<br />
  39. 39. Upper Header and Tube Installation<br />22<br />Confidential and Proprietary<br />
  40. 40. Upper Header and Tube Installation<br />23<br />Confidential and Proprietary<br />
  41. 41. Salt Piping<br />24<br />Confidential and Proprietary<br />All Salt Piping is Enclosed and Sloped Downward<br />
  42. 42. Steam Generator Layout<br />25<br />Confidential and Proprietary<br /><ul><li>Two-tank system provides 10 to 16 hours of thermal storage
  43. 43. 30-year design life
  44. 44. Either tank safely able to hold total salt inventory
  45. 45. Tank heel volumes minimized
  46. 46. 99% thermal storage efficiency</li></ul>Steam drum<br />Reheater<br />Evaporators<br />Superheaters<br />Preheater<br />Cold Tank<br />Hot Tank<br />
  47. 47. Steam Generator Building<br />Cold Salt Tank<br />Hot Salt Tank<br />Control Building<br />Receiver Tower<br />Plant General Arrangement<br />Turbine Generator Building<br />Receiver Assembly Area<br />Switchyard<br />Air Cooled Condenser<br />
  48. 48. Just a Pretty Little Cloud<br />
  49. 49. Direct Steam Versus Molten Salt<br /><ul><li>Rocketdyne is one of the few companies who can say they have experience with both direct steam and molten salt.
  50. 50. Solar One – 1979 – 1984 (Direct Steam)
  51. 51. Solar Two – 1994-1999 (Molten Salt)
  52. 52. Which fluid was best? Why?</li></ul>Direct Steam<br />SALT<br />Direct Steam<br />
  53. 53. The Advantages of Thermal Storage<br />Solar PV Varies Minute-to-Minute: Second-to-Second<br />Steam Drum Limits<br />
  54. 54. The Hot Tank is An Energy Integrator<br />The hot tank sums instantaneous energy flows.<br />The turbine sees the integral of these flows.<br />Collection may be interrupted by cloud passage – but not generation.<br />So cloud passage never interrupts generation during peak periods, it only brings forward the shut down late at night.<br />
  55. 55. Typical Solar Thermal Trough System<br />Solar field<br />Steam Cycle<br />Heated collecting main pipe<br />Steam turbine<br />Solar warmer<br />Electricity Generator<br />Natural<br />Gas<br />Boiler<br />Condenser<br />Eurothough Collectors<br />Solar steam generator<br />Degasification<br />Solar pre-warmer<br />Low pressure warmer<br />Water circuit pump<br />Solar warmer<br />Expansion Tank<br />Cooled collecting main pipe<br />Thermal fluid pump<br />Many solar plants need a gas boiler to maintain temperature on weak days.<br />
  56. 56.
  57. 57. At What Temperature Can You Store Heat?<br />.<br />Stored Heat =∑ mCpΔT<br />Salt<br />Therminol<br />Stored Heat is Proportional to ΔT<br />Large / Smaller ΔT ≈ 278°C/90°C<br />Low Temperature Storage Requires ≈ 3X mass<br />566°C<br />~378°C<br />288°C<br />288°C<br />Low Temperature Storage ~ 3X Cost per MWt<br />
  58. 58. Modular Multi-Plant Site<br />Multiple plants share:<br /><ul><li>Control room,
  59. 59. Warehouse, and spare parts inventory,
  60. 60. Administration building,
  61. 61. Operation and maintenance staff
  62. 62. Switchyard</li></ul>Modular - Multi-Plant Site<br />
  63. 63. What is the Optimum Receiver Size?<br />There Are Strong Economies of Scale!<br />Results of Thousands of Monte Carlo Analyses <br />Evaluating Plant Cost versus Receiver Size (MWt)<br />NORMALZIDED COST($/MW)<br />0<br />100<br />200<br />300<br />400<br />500<br />600<br />700<br />800<br />THERMAL POWER (MW)<br />Relatively flat curve between 500 and 650 MWt receiver sizes<br />
  64. 64. What is the Optimum Receiver Size?<br />There Are Strong Economies of Scale!<br />Multiple Towers of an Inefficient Size Only Multiply the Inefficiencies<br />NORMALZIDED COST($/MW)<br />0<br />100<br />200<br />300<br />400<br />500<br />600<br />700<br />800<br />THERMAL POWER (MW)<br />Relatively flat curve between 500 and 650 MWt receiver sizes<br />
  65. 65. Ten Towers Generate One Gigawatt (24x7)<br />1GW : 24/7 Solar Park Layout<br />12<br />Place picture of ten tower station here.<br />Control Room<br />And Common<br />Facilities<br />2500 meters<br />Each plant has standalone<br />Turbine and Steam Generator 1GW : 24/7 Solar Park Layout<br />12<br />Control Room<br />And Common<br />Facilities<br />2500 meters<br />Each plant has standalone<br />Turbine and Steam Generator <br />
  66. 66. 38<br />Confidential and Proprietary<br />Personal Experiences with Salt <br /> Personnel Hazard: <br /><ul><li> No burns to exposed skin
  67. 67. Clothing not ignited
  68. 68. Paper in Trash Can Not Even Singed</li></ul>ME<br />Trash<br />38<br />Confidential and Proprietary<br />
  69. 69. 39<br />Confidential and Proprietary<br />Personal Experiences with Salt <br />Personnel Safety: <br /><ul><li> No burns to exposed skin
  70. 70. Clothing not ignited
  71. 71. Paper in trash can not discolored</li></ul>Equipment Safety:<br /><ul><li> Salt washed off easily
  72. 72. No damage to paint
  73. 73. No burning, melting or chemical interaction with soft foam rubber gaskets or windshield wipers</li></ul>Trash<br />
  74. 74. 40<br />Confidential and Proprietary<br />How to Clean Up a Salt Spill<br /><ul><li> Wait ‘til the puddle freezes
  75. 75. Break up the frozen puddle with shovels
  76. 76. Load chunks of salt and sand into barrels
  77. 77. Haul barrels away</li></ul>Salt from a small flange leak is recoverable. Operators simply break off the frozen stalactite and throw it back in the tank. <br />Molten Salt Tank<br />Frozen Salt Puddle <br />Salt freezes within the top centimeter of soil, <br />Therminol stays liquid and seeps up to 5’ meters into the sand.<br />
  78. 78. 41<br />Confidential and Proprietary<br />How do you Decommission a Molten Salt System?<br /><ul><li> Erect a tall scaffold & wrap with tarps
  79. 79. Pump salt through a shower head at the top
  80. 80. Salt cools, solidifies and “prills” as it falls
  81. 81. Laborers load the prills into shipping bags
  82. 82. Sell as fertilizer</li></li></ul><li>Two Tank Molten Salt Storage Systems<br />Firm Dispatch – Enabling utility dispatch & curtail<br />Zero Fossil Fuel Combustion <br />Grid Stability – Stable output thru cloud transients. <br />Multiplied Peaking Capacity<br />Increased Annual Capacity Factor<br />Low Insolation Collection – For Hazy Days <br />Equipment Elimination <br />Eliminates Start Up Boiler<br />Eliminates Supplemental Firing for Superheat<br />