solar energy

Energy derived from the light and heat from the Sun. The amount of energy falling on just 1 sq km/0.4 sq mi is about 4,000 megawatts, enough to heat and light a small town. Solar heaters usually consist of concave mirrors or reflective parabolic surfaces that concentrate the Sun's rays onto a black (heat-absorbing) panel containing pipes through which air or water is circulated, either by thermal convection or by a pump. The heat energy of the air or water is converted into electrical energy via a turbine and a generator. Hot water for industrial and domestic use can be produced by circulating water through panels, the water absorbing heat from the Sun as it passes through the panels.

Solar energy may also be harnessed indirectly using solar cells (photovoltaic cells) made of panels of semiconductor material (usually silicon), which generate electricity when illuminated by sunlight. Although it is difficult to generate a high output from solar energy compared to sources such as nuclear or fossil fuels, it is a major non-polluting and renewable energy source used as far north as Scandinavia as well as in the southwestern USA and in Mediterranean countries.