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7.2.5 Concentrating Photovoltaic Power Plants
Photovoltaic cells can also be operated by concentrating sunlight. The main point
of this is that the concentration saves on valuable solar cell material. If sunlight is
concentrated by a factor of 500, the size of the solar cell can then also be reduced
by a factor of 500. The cost of the solar cell therefore becomes much less of an
issue. This means materials that ordinarily would be too expensive without solar
concentration could also be used. Concentrator cells therefore usually have higher
effi ciency than conventional photovoltaic modules.
There are many options for the concentration: for example, concentrator cells can
be mounted in the focal point of parabolic troughs or convex mirrors. One of the
main problems with this is effi cient cooling, because, in addition to the electric
energy of the solar cells, a large quantity of waste heat is produced. Flatcon technol-
ogy takes a different approach. A fl at Fresnel lens concentrates the sunlight onto a
concentrator cell that is only a few square millimetres in size (Figure 7.12 below
right). A copper plate on the back of the cell radiates the heat that accumulates
extensively towards the back. A concentrator module comprises a large number of
parallel cells. Many modules are then mounted together on a tracking device that
orientates the modules optimally towards the sunlight.
Figure 7.12 Photovoltaic system with concentrator cells. Photo/graphics: Concentrix Solar
GmbH.
7.2.6 Solar Chemistry
In addition to providing process heat or generating electricity, concentrating solar
thermal energy can also be used for testing materials or in solar-chemical systems.
For instance, there is a large solar furnace in the French town of Odeillo where a
large number of small mirrors are mounted on a hillside. These mirrors refl ect the
sunlight to a convex mirror 54 m in diameter, creating temperatures of 4000 °C in
the solar furnace, which is used for research and industrial processes. Solar furnaces
have also been built in Almería, Spain, and Cologne, Germany.
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