The direct conversion of solar energy may be achieved in several ways, e.g. electrically, chemically or thermally. For future commercial production of electrical energy, the use of concentrators to focus the energy onto banks of heat exchangers and thence to steam-generating plants seems the most likely. However, where a minimum of parts and a degree of transportability are required, the photovoltaic convertor, of which the silicon solar cell is perhaps the best known example, provides an excellent alternative.
Where no light is incident on the active face of a silicon solar cell it exhibits the normal forward and reverse-bias-characteristic curves of the p-n junction diode from which it is manufactured.