1. SOLAR THERMAL POWER
GEEN 4830 – ECEN 5007
7. Central Receiver Systems
Manuel A. Silva Pérez
silva@esi.us.es

2. Central Receiver Systems - CRS
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3. Solar Thermal Power Plant.
Basic configuration
Beam irradiance
Concentrator
Concentrated irradiance
Electricity
Receiver
Thermal energy
Thermal
Storage
Power
conversion
Fossil fuel Boiler system
Biomass
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4. Central Receiver System
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http://www1.eere.energy.gov/solar/power_towers.html
14/7/10

5. CRS (Gema Solar, Molten salts)
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6. CRS
(Phoebus, Open air volumetric receiver)
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7. Collector System (concentrator)
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8. Heliostat field
 The concentrator is the “heliostat field”, a Fresnel
concentrator
 Main elements
 Heliostat
 Control System
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9. The heliostat
 “an instrument consisting of a mirror mounted on an axis moved
by clockwork by which a sunbeam is steadily reflected in one
direction”
 Basic components
 Reflecting surface
 Structure and tracking mechanism
 Control system
 Typology:
 Glass - metal
 Stretched membrane
 Size: 1 m2 to 150 m2
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10. Heliostat
Incident ray
Reflected ray
Back support
structure
Elevation drive Reflecting surface
Azimuth drive
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11. Burning mirror, Hoesen (18th century)
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12. Glass – metal heliostat
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13. Heliostat
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14. Glass – metal heliostat
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15. Glass – metal heliostats
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16. Stretched membrane heliostats
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17. Stretched membrane heliostats
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18. Stretched membrane heliostats
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19. Reflectivity
 Reflectivity of a new, clean mirror ≈ 0.90 ÷ 0.94
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20. Mirror quality
 Heliostat facets are spherically curved
 For large focal distances, a parabolic surface can be approximated by
an spherical surface of radius r = 2f (f: focal distance).
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21. Mirror quality
 D   S   sp   c2
2 2 2
Ideal spherical curvature
 D   S   sp   c2
2 2 2
Spherical curvature, with waviness
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22. Distortion
 Spherical reflectors generate distortion of the image
 Dependent on time (relative position sun-heliostat)
Summer solstice, 7:30 a.m. Summer solstice, 7:30 p.m.
Summer solstice, noon
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23. Heliostat field layout
 Surround field
 North (south) field
 Secondary concentration
 Secondary concentrator optics tower (SCOT)
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24. North field
1000
800
600
400
200
0
-600 -400 -200 0 200 400 600
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25. Surrounding field
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26. Geometrical performance of heliostats
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27. Cosine factor
Yearly average cosine factor for a
north heliostat field
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28. Shading and blocking
Shading & blocking
Shading
Blocking
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29. Air transmittance
Air transmittance
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30. Spillage
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31. Receiver system
 Function
 Components
 Types of receivers
 Working fluids
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32. Receiver system
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33. Receiver types
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34. Cavity receivers
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35. Cavity receivers
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36. Molten salt cavity receiver
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37. External, cylindrical receiver
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38. External, cylindrical receiver
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39. External, cylindrical receiver
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40. Tubular receiver (boiler)
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41. Volumetric receivers
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42. Volumetric receivers
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43. Heat transfer characteristics of tubular and
volumetric receivers
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44. Detail of a volumetric absorber (wire mesh)
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45. Detail of a volumetric absorber
(ceramic cups)
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46. Working fluids
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47. Working fluids for CRS
 Water / steam
 Saturated steam
 Superheated steam
 Molten salts
 Air
 Pressurized
 Atmospheric
 Sodium
 Thermal oils
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48. Comparison of HTF’s
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49. Power conversion system
 Rankine cycle (steam turbine)
 Brayton cycle (gas turbine)
 Combined cycle (gas turbine + steam turbine)
 Stirling engines
 (MHD)
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50. CRS: pros and cons.
 Pros:
 Ability to achieve high temperatures
 Wide industrial base for most components
 Multiple technological options
 Technologically proven
 Multiple thermal energy storage options
 High potential for improved effciency or cost reduction
 Cons.:
 Complexity
 Short commercial record
 Best technology still undefined
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51. Energy Balance of Central Receiver
Systems
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52. High concentration concepts
 Secondary concentration
 Increase flux density on the absorber
 Reduce requirements for primary concentrator (heliostats)
 Secondary Concentrator Optics Tower
 The receiver can be placed at the ground level
 Solar Furnaces
 Very high concentration ratios
 Combine a field of flat heliostats and a parabolic concentrator
 Not for electricity generation
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53. Secondary concentrators
 REFOS Project (DLR)
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54. SCOT (Secondary Concentrator Optics
Tower)
 Weizmann Institute (Israel)
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55. SCOT (Secondary Concentrator Optics
Tower)
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56. Beam Down
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57. Solar Furnaces
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58. Solar Furnaces
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59. CRS projects
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60. CRS (PS10, sat. steam)
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61. PS10 and PS20 (Abengoa Solar, Spain)
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62. CRS (Gema Solar, Molten salts)
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63. Gema Solar (Torresol Energy, Spain)
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64. Gema Solar
Design Data
Total Reflective Area 285.200 m2
Number of heliostats 2480
Total Area covered by Heliostat Field 142.31 Ha
Thermal output of the Receiver 120 MWt
Tower height 120 m
Heat Storage Capacity (equivalent to turbine operation) 15 hours
Steam Turbine power 17 MWe
Natural Gas Thermal Power 16 MWt
Projected Operative Figures
Direct solar radiation over Heliostats 2062 kWh/m2
Annual Energy sales 96.400 MWhe
Contribution of Natural Gas 15%
Capacity utilization 65 %
CO2 savings 23.000 – 85.000 t/y
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65. Sierra Solar (e-Solar, USA)
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66. Unit #1 (100 kW hybrid GT) (Aora Solar,
Israel)
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