Solar Energy Perspectives - IEA

Solar Energy Perspectives: Solar thermal electricity
Manzanares in Spain in the mid-1980s. It would use the shallow layer of the ground or simple
water tanks in the greenhouse to level off the heat in the greenhouse and generate electricity
around the clock. It is adapted to sunny countries even without high DNI, as no concentration
of the solar resource is needed. The difficulty is that only very large systems would be
economic, as the power output depends on the squared power of the dimensions. Therefore,
moving from small-scale to mid-scale is uneconomic, while leapfrogging to large-scale
seems risky. One possible way forward may be to first develop mid-scale up draft towers as
dry cooling towers for CSP plants, avoiding having to bear the costs of the greenhouse, which
have recently been suggested to be three to six times greater than those of the tall tower itself
(Fluri et al., 2009).
Figure 8.8 Principle of a solar chimney
Chimney
Wind turbine
Glass roof
Source: Schlaich and Robinson, 1995.
Key point
Solar chimneys need to be gigantic to be cost-effective.
Other solar thermal electricity technologies have been suggested. Solar thermoelectric
generators could use the Seebeck or Peltier effects to generate electricity from heat – with no
moving parts, as with PV systems. They need no sun-tracking device, as they need not
concentrate the light of solar rays. Scientists at the Massachusetts Institute of Technology have
recently achieved peak efficiencies of 4.6% with high-performance nano-structured thermoelectric
material and spectrally-selective solar absorbers with high thermal concentration in
an evacuated environment. This is still far from being able to compete with PV, but if it can
be combined with heat storage it may open new avenues.
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