Solar energy is due to the fusion of hydrogen nuclei, as proton-proton cycle, which means, for this star, transformation, every second, about 4 million tons of its mass in energy (at this rate it can ensure a duration of about 100 billion years before it is exhausted the reserve of hydrogen). For Earth, the Sun represents a source of energy, 1 779 × 1 011 MW, which man uses directly or indirectly. The wind and other weather event, as well as the development of plant and animal life, are taking advantage of natural solar energy. In an artificial way, the man makes useful solar energy through the capture of solar radiation and its conversion to electricity using photovoltaic cells, which may be used in broadcasting, radio systems, pumping for irrigation, etc.. One of the largest projects of interest is the solar power satellite consists of a set of batteries and solar geosincrònica placed in orbit. Solar energy converted into electricity is transmitted to Earth via a microwave beam that captured antenna is converted into electricity. A direct use of solar energy at low temperatures (60-120 ° C) is carried out with solar plans that can be used for industrial and domestic heating in greenhouses, the desalination of sea water, etc. . At medium temperatures (150-300 ° C), solar energy can replace traditional fuels in power plants and processes (solar power). Through the concentration of solar collectors with parabolic can be reached at temperatures above 3000 ° C in the solar ovens useful in chemical treatments that require a source of clean energy. Encyclopèdia.cat.