The Sun is the main source of energy for the Earth. This energy is supplied mainly in the form of electromagnetic radiation.
Radiation from the Sun is absorbed by oceans, landmasses and the atmosphere and transformed into heat. The water cycle is also maintained by the Sun. The warming of the air causes water to evaporate and rise to higher layers of the atmosphere. Here clouds are formed which then release their water as rain; the heat from the Sun then causes the water to evaporate again, and so
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The plant world uses the energy from the Sun for photosynthesis. The Sun, as the supplier of energy, together with chlorophyll, as the catalyst, produces fuels such as wood, and indirectly fossil fuels such as coal and oil.
A direct use of the Sun's energy is possible today using photovoltaic cells. These are thin sheets of semiconductors (electric conduction capacity increases with temperature) such as silicone, which transform the radiation from the Sun into electricity. The photovoltaic cell reacts to certain frequencies of light by releasing charged particles. The electrons converge in a certain part of the cell, thus creating a light-induced voltage. This is increased when numerous small photovoltaic cells are linked in a large system referred to as solar panels. However, this type of energy generation is still very expensive for high-energy demands. They can be used for isolated households that are not connected to the national grid. It is important to take advantage of the seasonal variations in the amount of sunlight by storing surplus energy produced in the summer for the colder period. This is accomplished by simple ground or water storage systems (heating) or by more complicated methods where certain salts are used for temporary storage.
A greater degree of efficiency is achieved by solar energy plants that have one or more concave mirrors. Here the radiation from the Sun is reflected and collected in a receiver. The collected energy is amplified and the temperature rises to several hundred degrees Celsius. To ensure that the greatest possible amount of radiation is caught, the solar collector rotates to follow the position of the Sun.
Solar cells are widely used in watches and calculators, but also in space. Experiments with solar powered cars are still being carried out. The global market for solar technology is expanding rapidly as new applications are constantly being developed.
