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	Photovoltaic

	Cell
	Module
	Panel
	String
	Field
	Inverter

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The photovoltaic system is a set of mechanical, electrical and electronic components that concur to the capture and conversion of all available solar energy, making it usable in the form of electricity. This is done by exploiting a physical phenomenon, known as the photovoltaic effect (i.e., the ability of some suitably doped semiconductor materials to generate electricity when exposed to light radiation.
When photons (energy particles from the sun) strike a photovoltaic cell, a portion of energy is absorbed by the material and some electrons, displaced from their position in the atomic structure, flow through the (properly treated) semiconductor material, producing a direct current that can be collected on the surface of the cell.
More cells are connected in series or in parallel and packed to form a module, which is the basis of the photovoltaic implant.
PV systems can be divided into two categories: those connected to the electricity grid (grid-connected) and the isolated ones (stand-alone). In the first case, the current generated is sent to an inverter from which it comes out in the form of alternate current, which can then be transformed into medium-voltage current from the transformer before being fed into the distribution line. In the latter case however, that of the isolated plants, they can feed powerloads in both direct current (without the presence of an inverter) and alternate current forms, but they generally have a storage system. In this type of photovoltaic system it is necessary to store electricity to ensure the continuity of supply even at times when it is not produced. That is ensured by electrochemical accumulators.
The system connected to a network, however, does not incorporate storage systems because the energy produced during the hours of sunshine is fed into the power grid; vice versa during the hours of little or no sunshine, the local powerload is fed from the network.

Photovoltaic conversion, which was developed at the end of the 50s within space programs, is considered a technology that can significantly help meet the increasing global energy needs without greenhouse gas emissions.
This is why it attracts large investments, both for the construction of systems and for research and development of new materials and technologies that can reduce generation costs for each produced kWh.
Specifically, in the last few years the installed capacity worldwide, which was only 1,000 MW in the year 2000, is growing at an extremely fast rate. Major international energy agencies estimate that in 2020 the PV installed capacity worldwide will be as high as 56,000 MW, with an electricity production capable of meeting almost 2% of world demand.
Italy is not excluded from this development, since in this country distributed generation is growing at a pace that could have never been predicted just a few years ago. For example, in 2008 and 2009, about 70,000 PV systems were installed in Italy.
These plants have a limited capacity (up to 20 kW), allowing each home to become a small power station capable of meeting the needs of the family and, at the same time, to inject power in the public grid.