Solar energy

Solar energy, power derived from the sun. Because the earth's supplies of coal, petroleum, and other fossil fuels will eventually be exhausted, while the sun's energy will not, several methods of using solar energy have been developed. One is the solar furnace, basically a huge parabolic mirror that focuses the sun's heat onto a small area. Temperatures of more than 7,232°F (4,000°C) may be produced by this method. The heat can be used to raise steam and generate electricity, or for scientific research. In the Soviet Union a solar power station has been built with a system of 1,300 moving mirrors covering an area of 5 acres (about 2 hectares). It produces 2 1/2 million kilowatt-hours of electricity annually.

Solar energy is used increasingly for domestic heating. Heat is collected by exposing a large, darkened metal plate, covered with 1 or more layers of glass, to the sun. Water or air is passed through tubes attached to the plate and either circulated through the building or stored. Hot water is stored in insulated tanks. Hot air is passed through a tank full of rocks, which hold the heat until it is required to warm up air for circulation around the house.

Sunlight can also be converted directly into electricity in a solar cell, and there is research into the possibility of using sunlight to produce chemical energy by the same sort of reaction as photosynthesis in plants.

See also: Radiation.