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.
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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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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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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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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