Photovoltaic (PV) cells are based on semiconductors and convert light directly into electricity. They are usually encapsulated within modules with a power up to several hundred watts that can be combined into larger power arrays. These systems are connected to consumers or to the grid via electronics. Solar-photovoltaic technologies include off-grid and on-grid applications. PV systems are made either from crystalline semiconductor modules or from thin films, and PV technologies are characterized by their modularity.
The overall efficiency of systems available on the market varies between 6% and 15%, depending on the type of cell. Crystalline silicon has been the most important PV technology so far. Because of their extremely high cost, other crystalline technologies, such as gallium arsenide (GaAs), are used only in space exploration. The first thin film PV device, an amorphous silicon (a-Si) module, was developed in the 1980s. More recently, other semiconductors, including cadmium telluride (CdTe) and copper indium diselenide (CIS/CIGS), have been used in industrial module production. The potential for thin-film modules is considered very high, but so far their diffusion has been limited by their high cost.
Installed grid-connected capacity is mostly in Japan, Germany and the United States. These three countries account for about 85% of global PV capacity. PV is often perceived as economic only in niche applications, such as traffic lights, weather stations and stand-alone systems for isolated buildings. Stand-alone or off-grid PV systems are particularly well suited for remote areas.
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