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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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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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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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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