Solar Thermal Power Plants - Renewable Energy: Technology, Economics and Environment - page 211

Environmental analysis. Since the environmental effects of dish/Stirling plants
are very similar to those of solar tower power plants, they are discussed within the
scope of the corresponding chapters on solar tower power plants (see Chapter
5.2.2).

5.5 Solar updraft tower power plants

For a solar updraft tower power plant the three components of glass roof collector,
chimney and turbine are combined. The use of this combination for power genera-
tion was already described more than 70 years ago /5-26/.

Kaminröhre Kaminröhre Kaminröhre Chimney tube Chimney tube Chimney tube

Turbine Turbine Turbine Turbine Turbine Turbine

Kollektor Collector Kollektor Collector Kollektor Collector

Kollektor Collector Kollektor Collector Kollektor Collector

Fig. 5.24 Function principle of a solar updraft tower power plant

The principle, on which a solar updraft tower power plant is based, is shown in
Fig. 5.24. The incident direct and diffuse solar radiation warms the air below a
flat, circular glass roof, open at the circumference, which, in conjunction with the
bottom underneath, forms an air collector. The middle of the roof is equipped with
a vertical chimney provided with big openings for air supply. The roof is con-
nected air-tight to the chimney bottom. Since warm air is of lower density than
cold air, it rises to the top of the chimney tube. At the same time, the pull of the
chimney makes warm air flow from the collector inside the chimney, so that cold
ambient air flows inside the collector. Thus, solar radiation ensures continuous
updraft inside the chimney. The energy contained in the air flow can be converted
into mechanical energy using pressure-staged turbines, located at the bottom of
the chimney. Eventually the energy is transformed into electrical energy by means
of generators.
The achievable electrical output power P el of a solar updraft tower power plant
can be calculated according to Equation (5.6), namely on the basis of the supplied

solar energy G . g,abs and the power plant efficiency η PP . The latter in turn consists of