Photovoltaics technology is used so as to exploit the energy that arrives on earth’s surface through solar radiation. The average solar radiation that arrives daily on earth’s surface is 1 Kw/m2. The photovoltaic phenomenon is responsible for the conversion of solar energy to electric.
Silicon is until now the most important material in the production of solar cells since it constitutes the essential material for 90% of the international solar cells production. The most important types of solar cells are the following:
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Crystalline
Efficiency: 13-16%
Crystalline silicon is still the mainstay of most PV modules. Efficiencies of more than 20% have been obtained with silicon cells already in mass production. This means that 20% of the incoming insolation can be transferred into electricity. As well as the efficiency of the solar cells, their thickness is also an important factor. Wafers – very thin slices of silicon – are the basis for crystalline solar cells.
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Polycrystalline
Efficiency: 11- 14%
Polycrystalline cells, in opposition to the monocrystalline cells, consist of a series of different crystals of silicon that are attached so as to create a photovoltaic panel. These panels’s production procedure is of lower cost although the cost of cells production remains high. Also, they present a lower efficiency in comarison to monocrystalline panels.
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Thin film
Efficiency: 5-9%
Thin film modules are constructed by depositing extremely thin layers of photosensitive materials onto a low-cost backing such as glass, stainless steel or plastic. This results in lower production costs compared to the more material-intensive crystalline technology, a price advantage which is currently counterbalanced by substantially lower efficiency rates.
Three types of thin film modules are commercially available at the moment. These are manufactured from amorphous silicon (a-Si), copper indium diselenide (CIS, CIGS) and cadmium telluride (CdTe). All of these have active layers in the thickness range of less than a few microns. This allows higher automation once a certain production volume is reached, whilst a more integrated approach is possible in module construction. The process is less labour-intensive compared to the assembly of crystalline modules, where individual cells have to be interconnected.
