Photovoltaic’s (PV) is a method of generating electrical power by converting solar radiation into Direct Current (DC) electricity using semiconductors that exhibit the photovoltaic effect.

Photovoltaic power generation employs solar panels comprised of a number of cells containing a photovoltaic material. Materials presently used for photovoltaic’s include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium selenide/sulphide.

Due to the growing demand for renewable energy sources, the manufacture of solar cells and photovoltaic arrays has advanced considerably in recent years.

As of 2010, solar photovoltaic’s generates electricity in more than 100 countries and, while yet comprising a tiny fraction of the 4800 Gigawatt total global power-generating capacity from all sources, is the fastest growing power-generation technology in the world. Between 2004 and 2009, grid-connected PV capacity increased at an annual average rate of 60 percent, to some 21 GW.

Such installations may be free standing ground-mounted or built into the roof or walls of a building, known as Building Integrated Photovoltaic’s or BIPV for short. Off-grid PV accounts for an additional 3–4 GW.

Photovoltaic arrays are often associated with buildings: either integrated into them, mounted on them or mounted nearby on the ground.

Arrays are most often retrofitted into existing buildings, usually mounted on top of the existing roof structure or on the existing walls. Alternatively, an array can be located separately from the building but connected by cable to supply power for the building.

Building-integrated photovoltaic’s (BIPV) are increasingly incorporated into new domestic and industrial buildings as a principal or ancillary source of electrical power. Typically, an array is incorporated into the roof or walls of a building.

The power output of photovoltaic systems for installation in buildings is usually described in kilowatt-peak units (kWp).