Photovoltaic

The photovoltaic phenomenon was discovered in 1839 by Edmund Bequerel who noticed that at some electro-chemical configurations it is possible to produce electric energy through the influence of solar radiation. However, it was only after the year 1954 when people started to use the photovoltaic phenomenon for the direct change of the solar radiation's energy into electric energy.

The principle consists in the fact that a photon which lands on a semiconductive structure with a PN transition excites an electron and so it creates two carriers of electric current: a free electron and a hole. The solar cells consist of two silicon layers. The upper silicon layer is a semiconductor of type N (the conductivity is enabled by electrons), the lower silicon layer is a semiconductor of type P (the conductivity is enabled by so called "holes"). If a photon gets near to a PN transition, a photo-effect occurs and the released electrons start to pass into the upper layer.

The electrons in the lower layer start to skip from one atom on the other in order to fill up the empty spaces. The free electrons in the upper layer are lead from the cell into the electric circuit into which the solar cell is embedded. In this way electric current arises in the circuit during the time when light falls on the solar cell. The electric energy is produced through this way noiselessly, without any moving parts and without by-products. The photovoltaic system works automatically, without any attendance and without large demands on maintenance.

Photovoltaic panels which are assembled from cells use the energy that is free of charge, that's why the operating costs of photovoltaic panels are negligible, moreover these panels are very reliable. An advantage of the photovoltaic is that it is possible to simply add panels and in this way to increase the performance of the whole plant. The owner of this plant can increase its power according to the increasing energy consumption. The panels and also the other parts are portable, so it is possible to install them on any place without problems.

Nowadays, solar cells are not only used in the production of panels, but many companies install them into roofing material or into outdoor materials for facades of buildings. The installation of solar cells into construction elements decreases the costs considerably, whereby solar cells look on buildings very aesthetically.

A photovoltaic field (row) is created through the connection of photovoltaic panels. Solar panels are produced in several power classes. The nominal output direct voltage is 12 V for accumulators, in the grid the value is 30-300 V. The power supplied by solar panels is unstable and it depends on the intensity of sunshine.

Solar cells work also when the sky is cloudy thanks to diffused light, even though their performance is then significantly lower (ca 10 % of the maximum). In winter there is less sunshine than in summer and that's why less electric energy is produced. The operational life of solar panels lasts 20 years and more.