Central Receiver Systems (CRS) are a type of solar thermal power plant that uses an array of tracking mirrors called heliostats to reflect and concentrate sunlight onto an elevated receiver. The receiver is located in a tower and absorbs the concentrated sunlight, converting it to heat which is then used to drive a power generation system. Key components of a CRS include the heliostat field, receiver, thermal energy storage system, and power block. Heliostats focus light onto the receiver to achieve high temperatures suitable for electricity production.

1. Central Receiver Systems - CRS
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2. Solar Thermal Power Plant.
Basic configuration
Beam irradiance
Concentrator
Concentrated irradiance
Electricity
Receiver
Thermal energy
Thermal
Storage
Power conversion
system
Fossil fuel Boiler
Biomass
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3. Central Receiver System
http://www1.eere.energy.gov/solar/power_towers.html
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4. CRS (Gema Solar, Molten salts)
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5. CRS
(Phoebus, Open air volumetric receiver)
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6. Collector System (concentrator)
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7. Heliostat field
} The concentrator is the “heliostat field”, a Fresnel
concentrator
} Main elements
} Heliostat
} Control System
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8. 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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9. Heliostat
Incident ray
Reflected ray
Back support
structure
Elevation drive
Reflecting surface
Azimuth drive
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10. Burning mirror, Hoesen (18th century)
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11. Glass – metal heliostat
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12. Heliostat
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13. Glass – metal heliostat
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14. Glass – metal heliostats
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15. Stretched membrane heliostats
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16. Stretched membrane heliostats
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17. Stretched membrane heliostats
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18. Heliostat field layout
} Surround field
} North (south) field
} Secondary concentration
} Secondary concentrator optics tower (SCOT)
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19. North field
1000
800
600
400
200
0
-600 -400 -200 0 200 400 600
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20. Surrounding field
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21. Geometrical performance of heliostats
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22. Cosine factor
Yearly average cosine factor for a
north heliostat field
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23. Reflectivity
} Reflectivity of a new, clean mirror ≈ 0.90 ÷ 0.94
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24. Shading and blocking
Shading & blocking
Shading
Blocking
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25. Air transmittance
Air transmittance
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26. 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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27. Mirror quality
σ D = σ S + σ sp + σ c2
2 2 2
Ideal spherical curvature
σ D = σ S + σ sp + σ c2
2 2 2
Spherical curvature, with waviness
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28. 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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29. Spillage
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30. Receiver system
} Function
} Components
} Types of receivers
} Working fluids
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31. CRS – Sistema Receptor
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32. Tipos de receptores
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33. Cavity receivers
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34. Cavity receivers
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35. Receptor - Fluidos de trabajo
} Características térmicas apropiadas: capacidad térmica,
entalpía de cambio de fase, estado a temperatura
ambiente
} No corrosivo, tóxico o inflamable
} Abundante, barato, tecnología de manejo asequible...
} No existe el fluido perfecto: hay que llegar a
compromisos
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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. Heat transfer characteristics of tubular and
volumetric receivers
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42. Volumetric receivers
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43. 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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