Solar cell

The black pallets you see on roofs or the grey little roofs you can see over meteorological stations in remote areas are solar cells. The solar cell works making use of the photovoltaic effect, that is generating voltage from the energy of the sun. For this we need two semi-conductors, e.g. two kinds of silicon. If a junction of such semiconductors is lighted, the energy of the light will separate the charge carriers from one of them and enable them to travel to the other one. In one of the semiconductors there is electron deficiency whereas in the other there is excess of them. Thus electric voltage is created.

The operation of such a junction is not easy, not to mention its cost. The silicon has to be of a specific kind, with the admixture of boron ( p-type) or with the admixture of phosphorus ( n-type). The light has to possess enough energy and the resulting voltage is always lower than the light energy. Cheap silicon cells produce only 0.4 volt.

Solar cells are used to power artificial satellites, space probes, calculators and watches.