There are different ways in which the sun’s power can be used. Solar thermal energy is obtained by converting solar heat into useful heat, for warming shower water or heating, for example.
Photovoltaics is where solar radiation is converted into electrical energy. In order to do so, individual solar cells are combined to create solar modules. Solar cells consist of a semi-conductor material (generally silicon) in which light irradiation is separated into negative (electrons) and positive charge carriers.
An electric field created by selected imbalances in the semi-conductor separates the charge carriers. The result is a lack of electrons on one side and a surplus of them on the other. This electrical tension can be collected with a metal contact on the upper and lower sides.
In 1839, the French physicist, Alexandre Becquerel, discovered the photovoltaic effect, by which pairs of electrical charge carriers are separated when hit by sunlight. In 1884, the American Charles Fritts described the electromotive force in illuminated selenium and constructed the first solar cell. Its effectiveness was, however, minimal.
The scientific explanation for the fact that light can be converted directly into electricity was provided by Albert Einstein in 1905. His essay on the law of the “photoelectric effect” supplied the foundation for modern photovoltaics. In the end it was a coincidence which led to the modern solar cell.
Calvin Fuller and Gerald Pearson were actually developing the transistor and created the solar cell almost as a by-product of an experiment. Together with their colleague Darryl Chapin, the researchers presented their silicon-based "Solar Energy Converting Apparatus" in 1953. The breakthrough had been made.
As early as 1958, the first satellite fitted with a photovoltaic energy device was floating through space. Today, energy supplied by photovoltaic modules is standard for spacecraft. At first, photovoltaics remained an expensive form of technology used only for special applications. But then the oil crisis in 1973 and the Chernobyl reactor catastrophe in 1986 spurred on the search for new, regenerative sources of energy.
The conversion of sunlight into electricity and warmth experienced a real boom and, finally, became affordable for private households. Today, thin-film solar cells are being produced. They are particularly cost-effective as only very little silicon is required to make them. The cells are vapour deposited onto a medium such as glass and can then be installed easily on facades for instance.