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Cu stp 04_fundamentals
1. SOLAR THERMAL POWER!
GEEN 4830 – ECEN 5007!
4. Fundamentals of solar thermal concentrating systems!
Manuel A. Silva Pérez
!
silva@esi.us.es !
2. Solar Thermal Concentrating
Systems
Systems that make use of solar energy by first
concentrating solar radiation and then converting it
to thermal energy
} Uses:
} Electricity (Solar Thermal Power)
} Industrial Process Heat
} Absorption cooling
} Chemical processes
} …
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3. Solar energy
} Abundant
} High-quality energy
} Variable (on time)
} Unevenly distributed (on space)
} Low density
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7. Ideal concentrating system
} The receiver (or absorber)
converts concentrated
solar radiation to thermal
energy (heat)
} An ideal receiver may be
characterized as a
blackbody, which has only
radiative losses
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GEEN 4830 – ECEN 5007
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8. Geometrical concentration ratio
} The geometrical
concentration
ratio, Cg, is
defined as
A Concentrator
Cg = C
Aabs
Where Aabs is the
receiver (or
Collec'on
absorber) area area
Absorp'on
and Ac is the area
collection area.
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10. Ideal concentrator
} The maximum theoretical optical efficiency (when
Tabs≥TSky) is the effective absorptivity of the receiver.
} The higher the concentrated solar flux (C*I), the better
the optical efficiency.
} The higher the absorber temperature, the higher the
radiative loss and, therefore, optical efficiency is lower.
} The higher the effective emissivity, ε, the lower the
optical efficiency.
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11. Global efficiency of the ideal concentrating
system
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12. Ideal concentrating system
} For each value of the geometrical concentration ratio,
there is an optimum temperature.
} The higher the geometrical concentration ratio, the
higher the optimum temperature and the global
efficiency.
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GEEN 4830 – ECEN 5007
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13. Concentration limits
} The Sun is not a point light source.
Seen From the Earth, is a disk of
apparent diameter θS ≈ 32’.
} The maximum concentration ratio is
given by 32’
n′2
C max,3D = 2 2
n sen θ S 32’
Focus
Where n and n’ are the refractive indices of
the media that the light crosses before
and after the reflection on the
concentrator surface
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GEEN 4830 – ECEN 5007
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14. Types of concentrating systems
} Line focus (2D)
} Parabolic troughs; CLFR
Cmáx,2 D = 1/ sin θ S
} Point focus (3D)
} Central receiver systems,
parabolic concentrators
(dishes)
Cmáx ,3D = 1 / sin θ S 2
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GEEN 4830 – ECEN 5007
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