A fraction of all the energy from the everlasting fusionprocess on the sun hits Earth. The incoming radiation can either be considered a wave movement, where sunlight include the whole visible spectrum plus infrared and ultraviolet light, or it can be seen as small energy packages, photons, that travel with the speed of light.
Man has used the sunlight for a long time – either passive, for for example heating of houses, or, in the last fifty years, active, to gain solar heat or solar electricity.
In a solar heating system there is a medium, usually water, which is heated by the sun. The water then transfers its heat to a water storing tank. An automatic regulation system controls the whole thing. Efficiency rates up to 60 % have been observed.
Direct transformation of sunlight to electricity is done in solar cells, or photovoltaic cells which is another name for the same thing. The photonenergy sets electrons loose from atoms. The electrons are then being led through a semi-conductor with an electrical field. The electricity is either used immediately, as in calculators, accumulated with batteries or transfered to the power lines.
Silicon in crystal form started the whole thing and has today the highest efficiency rate on 30 %. These results have only been achieved in laboratories however, a more common rate is about 20 %. The cheaper and less efficient cells with thin layers can compete as they demand much less material.
It is also possible to make electricity out of sunlight using so called thermal solar energy. It works as a conventional steam power plant with turbines and generators but the sun produces the steam, in this case.
Solar energy has today an extremely small part of the energy market, but can and will probably be one of the best energy sources. Especially when you consider that solar energy devices, when they’re up and running, don’t pollute and has no combustion.