A photovoltaic solar plant is a facility which allows to produce electricity using the solar radiation energy.
Electric energy production is carried out through a physical mechanism (photovoltaic effect) which involves semiconductor material’s electrons (Silicon) when it absorbs photons from the solar radiation.
With a photovoltaic plant you could produce electric energy for free or even earning money without emissions of pollutants and saving fossil fuels.
The disadvantages of this kind of plant are the variability and unpredictability of the energy source, the considerable starting cost and the wide areas needed. In spite of this, a photovoltaic plant allows to produce energy even in peculiar situations, for example in a remote village without electricity network.

A photovoltaic plant is made of several photovoltaic modules. Each module is a panel in which there are photovoltaic silicon cells: they allow the conversion from solar energy into DC electric energy.
The most common photovoltaic cells are made of:
Monocrystalline silicon: Cells are extracted from a single crystal silicon bar, as a consequence manufacturing costs are high and wastes are considerable. The efficiency of modules made of monocrystalline silicon cell is 16-17%, it is the highest between the various photovoltaic modules.

Polycrystalline silicon: Cells are extracted from silicon bars made of several disordered crystals and produced by melting and crystallization of silicon wastes. The efficiency of modules with polycrystalline silicon cell is 14-15%.
Amorphous silicon: Cells are very cheap, silicon doesn’t have a crystalline structure and efficiency is low, about 8%.
Photovoltaic panels could be laid down on an horizontal or tilted area with a southern exposure (roof, terrace, field …); one of the prerequisite is that the area should not be covered by any shadow coming from trees, mountains, buildings, etc... during the day. For this reason it is necessary to go on with a careful design of the plant not to cause panels shadowing other panels, especially in big plants.
Installation areas have to be wide depending on the power of the plant, usually 5-7 m2 are needed for 1 kWp.
For the installation and the start-up of the plants you need:
Support structures for the panels: In Italy the photovoltaic panels must be installed with a 30° tilt angle, in this way their efficiency is the best. Support structure are made of metal and they are fixed to the installation surface with anchorages. There are also mechanized support structure (solar tracker) that sense the direction of the sun during the day and, as a consequence, they tilt the panels in order to have the maximum exposure to the light.
Inverter: It is an electronic device which can turn DC into AC in order to use it directly in houses or feed it into the electricity network. Normally inverters have a protection device and an interface which can swich off the plants in case of black-out or network troubles.
Control system: It is an electronic device which communicates with inverter and with any other sensor. This instrument allows to control how the plant works, to register data on the PC and to show some of the data on screens or displays. There are sophisticated applications which permit to send data and warning messages by e-mail, internet or text messages in case that there is a fault in the plant.
Energy meter: It is a meter which shows how much electricity you generate, how much of it you use and how much electricity you feed in the network.
The installation of a photovoltaic plant may be in keeping with the place it is put in, it depends on the specific characteristic of the area.
A photovoltaic plant will last for about 25 years, as it is modular it is possible to easily replace any damaged item.
Every photovoltaic panel will have a loss of efficiency: for monocrystalline and polycrystalline panels this loss is lower than the 20% during the first 25 years. Amorphous silicon panels have a 30% loss of efficiency in the early months, than they reach a steady state.
Inverter is the only device which has a lifetime shorter than modules, even if it’s long too. However it is a cheap device and it could be easily changed.
A photovoltaic plant is about 3000-5000 €/kWp. A high starting investment is needed, especially for big plants, but, considering that these plants benefit from the feed-in tariff, in 8-10 years you cover the costs of the plant.
After the amortization time and considering that a plant lasts for 25 years, the final budget will have a positive variance.
If you install a photovoltaic plant which feed in the electricity network, you can access the “feed-in tariff”.
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