Environmental Engineering Reference
In-Depth Information
7.2.3 Dish-Stirling Power Plants
Whereas trough and tower power plants are only economically viable in large-scale
applications of many megawatts, the so-called Dish-Stirling systems can also be
used in smaller units - for example, to supply remote villages or towns. With Dish-
Stirling systems a convex mirror in the form of a large dish concentrates the light
onto a focal point. To ensure that the light is concentrated as strongly as possible,
the mirror is dual-axis tracked very precisely towards the sun.
A receiver is sited at the focal point. This receiver transfers the heat to the actual
heart of the system: the Stirling engine. This engine converts the heat into kinetic
energy and drives a generator that ultimately produces electric energy.
A Stirling engine can be driven not only by the heat of the sun but also through
combustion heat. In combination with a biogas burner these plants can also generate
electricity at night or during periods of bad weather. And the use of biogas also
makes them carbon - neutral.
Some prototypes of pure solar systems have been built in Saudi Arabia, the USA
and Spain (Figure 7.10). Compared to tower and trough power plants, the price per
kilowatt hour with Dish-Stirling systems is still relatively high. The costs would be
reduced considerably if large unit quantities could be mass produced.
Figure 7.10
Prototype of a 10-kW Dish-Stirling system near Almería in Spain.
7.2.4 Solar Chimney Power Plants
There is a big difference between solar chimney power plants and the thermal plants
described earlier. While solar thermal power plants work by concentrating sunlight,
solar chimney power plants function through the heating of air. The collector fi eld
is formed by a large fl at area that is covered by a glass or plastic roof. A high
chimney is located in the middle of the area, and the collector roof rises gently in
