Thermoelectric Topping Cycle for Trough Solar Thermal Power Plants

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presented at Material Research Society (MRS) conference, Boston MA, 2009

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Thermoelectric Topping Cycle for Trough Solar Thermal Power Plants

  1. 1. 1 Thermoelectric Topping Cycle for Trough Solar Thermal Power Plants Presenter: Andy Muto Advisor: Gang Chen NanoEngineering Group, MIT MRS Conference, 12/2/09 NanoEngineering Group
  2. 2. 2 Solar Thermal Power -most attractive solar technology for utility scale -uses conventional steam Rankine cycle -allows for 6-15 hrs thermal storage NanoEngineering Group
  3. 3. Solar Thermoelectric Topping Cycle 3 Vacuum Heat Transfer fluid outlet Enclosure temperature is limited to 400°C Thermoelectric Characteristics: Low Temp Absorber Fluid -high power densities -reliable, no moving parts, no Thermoelectric Elements maintenance -inexpensive High Temp Absorber -low efficiency NanoEngineering Group
  4. 4. 4 Thermoelectric Conversion Efficiency Carnot Limit ZT=15 Solar Rankine ZT=3 ZT=2 ZT=1 NanoEngineering Group
  5. 5. 5 Thermoelectric Conversion Efficiency Carnot Limit Topping ZT=15 Cycle Solar Rankine ZT=3 ZT=2 ZT=1 NanoEngineering Group
  6. 6. 6 Thermoelectric Conversion Efficiency Carnot Limit Topping ZT=15 Cycle Solar Rankine ZT=3 ZT=2 ZT=1 NanoEngineering Group
  7. 7. 1-D Model 7 fluid tube wall P N absorber Csolar  qloss glass  Abs  Csolar Csolar qloss NanoEngineering Group
  8. 8. 1-D Model 8 fluid tube wall ZTeff 1 1 W TE AbsC,TE P N TE Tf ZTeff 1  Tabs Carnot efficiency absorber Csolar  qloss glass  Abs  Csolar Csolar qloss NanoEngineering Group
  9. 9. 1-D Model 9 WTE  WRankine Rankine  sys  WRankine Csolar fluid  Rankine  C , Rankine II , Rankine  Abs  TE  tube wall ZTeff 1 1 W TE AbsC,TE P N TE Tf ZTeff 1  Tabs Carnot efficiency absorber Csolar  qloss glass  Abs  Csolar Csolar qloss NanoEngineering Group
  10. 10. 10 Surfacevs. Wavelength Intensity Properties 1.4 Absorptivity=0.96 1.2 Glass transition λ=2700 nm Transmissivity=0.963 (λ<2700 nm) 1 Emissivity=0.89 (λ>2700 nm) Solar Intensity [W/m2/nm] Intensity [W/m2/nm] Surface Emissivity 0.8 0.6 0.4 0.2 Emissivity=0.05 0 500 1000 1500 2000 2500 3000 3500 4000 Wavelength [nm] NanoEngineering Group
  11. 11. 11 Optimal Transition Wavelength Intensity vs. Wavelength 60 Solar at 40 times concentration 50 transition TAbs , Csolar  Intensity [W/m2/nm] 40 30 20 Black Body 700°C 10 Blackbody 400-700°C by 50°C increments 0 500 1000 1500 2000 2500 3000 3500 4000 w avelength [nm] NanoEngineering Group
  12. 12. Absorber Efficiency Intensity vs. Wavelength Rankine Topping Cycle 60 [W/m2/nm] 1.4 1.2 Topping cycle 55 1800 nm 0.9 1 0.92 0.88 95.6% Solar Intensity/nm] 50 0.8 0.82 Concentration [suns] 0.86 0.8 0.84 2 Intensity [W/m 0.6 Original cycle 45 0.7 0.76 .78 2500 nm 0 concentration 0.4 99.1% 40 0.2 35 4 0 500 1000 1500 2000 2500 3000 3500 4000 30 Wavelength [nm] 25 20 Absorber Efficiency 15 Absorber Efficiency decreases rapidly with increasing temperature 10 200 300 400 500 600 700 due to blackbody overlap with solar absorber Temperature [C] spectrum Absorber Temperature [C] NanoEngineering Group
  13. 13. Decision to Implement TE Topping Cycle with TE Topping cycle should produce 10% more Pratio  without power to justify added engineering costs Vacuum Enclosure Low Temp Absorber Fluid Thermoelectric Elements High Temp Absorber NanoEngineering Group
  14. 14. Decision to Implement TE Topping Cycle with TE Topping cycle should produce 10% more Pratio  without power to justify added engineering costs 60 55 50 Power Ratio concentration [suns] 45 ZT=1 40 1.1 5 1.0 5 1.1 35 concentration [suns] 30 Implement Do Not Implement 25 20 15 10 150 200 250 300 350 400 450 500 fluid temperature [C] NanoEngineering Group
  15. 15. Decision to Implement TE Topping Cycle with TE Topping cycle should produce 10% more Pratio  without power to justify added engineering costs 60 55 50 Power Ratio concentration [suns] 45 ZT=1 40 1.1 5 1.0 5 1.1 35 concentration [suns] 30 Implement Do Not Implement 25 20 15 10 150 200 250 300 350 400 450 500 fluid temperature [C] NanoEngineering Group
  16. 16. Decision to Implement TE Topping Cycle with TE Topping cycle should produce 10% more Pratio  without power to justify added engineering costs 60 55 1.4 1.1 5 1.0 5 1.3 1.1 1.2 50 1.45 concentration [suns] 45 1.35 1.2 5 40 35 concentration [suns] 1.5 30 Power Ratio ZT=3 25 20 15 10 150 200 250 300 350 400 450 500 NanoEngineering Group fluid temperature [C]
  17. 17. Optimal Absorber Temperature, ZT=3 60 55 65 0 50 concentration [suns] 45 625 40 35 60 0 30 57 5 25 Optimal Temperature ZT=3 55 0 500-600°C 20 52 5 15 500 10 150 200 250 300 350 400 450 500 fluid temperature [C] NanoEngineering Group
  18. 18. 18 Conclusions •investigated a thermoelectric topping cycle for parabolic trough solar thermal power plants •current materials with ZT=1 will not work in this application •ZT=3 or greater is needed, with operating temperatures around 500-600°C •other applications may exist within solar thermal energy at lower temperatures Acknowledgements: KFUPM NanoEngineering Group
  19. 19. Power Ratio ZT=3 Emissivity=0 with TE Pratio  without 60 55 1.5 1.4 50 concentration [suns] 45 1.25 1.3 5 1.4 5 1.2 1.1 5 40 1.3 1.1 35 30 25 1.05 20 15 10 150 200 250 300 350 400 450 500 NanoEngineering Group fluid temperature [C]
  20. 20. Limits to ZT=1 applications 20 3 Power Ratio ZT=1, emissivity=0 10 1.2 1.1 1. 05 1. 2 1. 1 1. 05 concentration [suns] 2 10 1.2 1 1. 5 1. 0 1 1 1 10 100 200 300 400 500 600 700 fluid temperature [C] NanoEngineering Group
  21. 21. Efficiency Gain ZT=3  gain   with TE   without 60 55 0.1 2 50 2 concentration [suns] 45 0.0 0.0 8 0.0 6 0.0 4 0.1 40 35 30 25 20 15 0 10 150 200 250 300 350 400 450 500 fluid temperature [C] NanoEngineering Group
  22. 22. 1-D Heat Loss 22 Tabs absorber 1  1   A  A 1 1 AVF AglassVF 1   glazing  glazing Aglazing qloss A Tglazing glass 1 1    , glazing UAglazing   , glazing Aglazing 1 AglazingVF 1    , 1    ,   A   A T qloss  qabs  glazing  qtransmit  qglazing   qtransmit  qconvection NanoEngineering Group
  23. 23. 1-D Model 23 WTE  WRankine  sys  Csolar  II , Rankine  0.65  Rankine  C , Rankine II , Rankine  Abs  TE   ZT  15 ZTeff 1 1  II ,TE TE AbsC,TE ZT ZTeff 1  Tf Tabs 1 0.20 Carnot efficiency 2 0.30 3 0.37 Csolar  qloss  Abs  Csolar NanoEngineering Group
  24. 24. 24 U.S. Concentrating Solar Resource NanoEngineering Group

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