Solar Energy Perspectives - IEA

Solar Energy Perspectives: Solar thermal electricity
will allow dishes to compete with larger solar thermal systems. However, uncertainties
relative to technology development and costs have so far prevented large projects in the
hundreds of megawatts.
Balance of plants
As in other thermal power generation plants, CSP requires water for cooling and
condensing processes. CSP water requirements are relatively high: about 3 000 L/MWh
for parabolic trough and LFR plants (similar to a nuclear reactor) compared to about
2 000 L/MWh for a coal plant and only 800 L/MWh for combined-cycle natural gas
plants. Dishes or Brayton cycle towers are cooled by the surrounding air with no need for
cooling water.
Figure 8.4 Concept of combined-cycle hybrid solar and gas tower plant
with pressurised-air receiver
To solar receiver
Tower
Hybrid cycle
Air
intake
Gas turbine
Solar field
Solar
receiver
Fuel
Combustion chamber
Bottoming cycle
Heat recovery
steam generator
Steam
turbine
Cooling system
Source: PEGASE/CNRS.
Key point
Small-scale air receivers for towers have been successfully tested.
Dry cooling (with air) is one effective alternative used on the ISCC plants in North Africa
(Photo 8.3). Various dry cooling systems have been used for large fossil-fuelled steam plants
in arid areas for at least 50 years, so maturity is not an issue. However, dry cooling costs more
and reduces efficiencies by up to 7%.
There are other options, though. Hybrid wet/dry cooling systems reduce water consumption
while minimising the performance penalty. For a parabolic trough CSP plant, this hybrid
approach could reduce water consumption by 50% with only a 1% drop in annual
electrical energy production. Another, more speculative option would be to build very tall
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© OECD/IEA, 2011