Light generates an electric current when it falls on certain substances and releases electrons from their atoms. The electrons are then available to flow through a circuit.
A typical photovoltaic cell is the silicon solar cell. Each silicon cell is formed from a wafer of pure silicon to which selected impurities have been added. The surface that is exposed to light is treated with boron or a similar element. The rest of the silicon is treated with an element such as arsenic. When light strikes the boron-treated surface, it releases electrons which then tend to move into the arsenic-treated layer. The surface is the positive electrode; the arsenic-treated layer is the negative electrode. When the two electrodes are connected by a wire, current flows from the arsenic-treated layer through the wire to the boron-treated surface.
Solar batteries power most artificial satellites. On earth they are used to power communications equipment, navigational buoys, and pumping stations, particularly at remote locations. Because solar batteries operate only when the sun shines, they are usually used with storage batteries if continuous power is needed.