Sunday, February 8, 2009

Solar Energy

Man has realized that solar energy is a reliable source of energy to meet his energy needs of the century. After all, he has already experienced it for the sun’s rays have been used as heat source for evaporating and distilling water, for salt production and for drying fruits, vegetables, fish and meet. And then, there is solar cooking and other such utilities.

The life of the sun is said to be about 5 billion years; naturally it’s a large and renewable resource. Besides, solar energy has few negative environmental impacts. However, its energy is diffused. Most applications of solar energy rely on systems consisting of collectors, storage and control. Control makes sure that the collection and storage systems operate safely and efficiently.

Solar energy is captured through ponds, collectors and cells. An artificial solar pond has dissolved salt at three levels – at 1.5ft, at 5ft and at much deeper level. It is at the third level with the densest, heaviest water where tapped heat is stored. However, the pond can retail only 10 to 20 percent of the energy. Solar collectors absorb solar energy and produce heat. They are used for space heating and cooling and for heating water. The solar collector is usually a simple blackened copper, aluminium or steel heat – absorber plate which readily absorbs sunlight, covered by a sheet of glass which does not transmit the longer wavelengths emitted by metal. A heat-transfer liquid circulates through a set of tubes and removes the heat from the plate. A typical space-heating system consists of a roof-mounted collector array whose tilt angle is equal to the latitude plus 15°, a heat-storage tank, pumps or a fan and a network of pipe or ducts for distribution of heat. It uses a liquid or air as the transfer medium. Solar cells directly convert sunlight into electricity. It consists of two layers of material, one of which is impregnated with an impurity such as boron or arsenic to make it negative and the other of which is similarly doped to make it positive. The elements silicon and germanium are used as semiconductors. One layer must be extremely thin for sunlight to penetrate. Pocket calculators work on solar cells. Small arrays of solar cells charge batteries and they power irrigation pumps and refrigerators where there is no commercial electricity.