Photovoltaic refers to the direct transformation of the energy contained in the sun's rays into electric current by an intermediary of solar cells and modules. A solar cell is a very thin plate made mostly from silicium-based compartments. The contact points between the battery and the solar cell conduct the generated current. The aligned solar cells (protected from bad weather by glass or plastic) make up the final product, the photovoltaic module. The usual unit of measure of the energy produced by the photovoltaic cell or maximum productivity of a solar cell is called the Wattpeak.