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PV can be used for very small appliances, where other sources, for instance diesel, are operating far below their nominal capacity and are therefore relatively expensive.
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Thanks to the modular character it is easy to enlarge a system to provide more energy or add more applications to it.
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PV has no moving parts, therefore repair is almost never needed and the maintenance requirements are moderate.
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When well designed a system operates very reliable.
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No fuel is needed.
The design of a PV-system, modules together with modules storage and electronic equipment, has to be carried out very carefully. Many of the unfortunate experiences with PV were related to a bad system design. PV can be very reliable as has been demonstrated in telecommunication projects where PV was chosen specifically because of its reliability, the same applies to buoys along the rivers and coasts. Even in The Netherlands with its small amount of sunshine and its large electricity grid, newly installed buoys are all PV powered. 2.2 Solar cells Solar radiation can be converted directly into electricity using semiconductor devices, which are known as photovoltaic (PV) cells. The most commonly used material is silicon. By diffusing phosphorus or boron into the silicon it is possible to create p- and n-type silicon, each with its own electrical characteristics. A thin silicon wafer is divided into two layers. Both layers are provided with metallic contacts. When sunlight falls upon the solar cell a part of the light is absorbed. The energy of the light releases electrons inside the silicon. When both sides of the cell are connected an electric current will start flowing. The size of the current depends upon the intensity of the incoming radiation. Not all the energy of the light is converted into electrical energy.
Fig.4: Schematic cross view of a silicon solar cell There are a number of semiconductor materials from which solar cells can be made. Until recently the most commonly used was mono-crystalline silicon. At the moment polycrystalline and amorphous silicon are becoming more important. Table 2 gives the theoretical and achieved conversion efficiencies for a few types of solar cell materials.
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