ss of the lost radiation, the solar energy that reaches the surface of the Earth is 10,000 times the energy used by the people (Solar energy in McGraw-Hill Concise Encyclopedia of Science and Technology, 2004).
The radiation which is scattered when it collides with gas molecules is termed diffuse radiation, whereas the portion that directly reaches the Earth’s surface is termed direct radiation. Clouds play an important role in the scattering of radiation and hence reduce direct radiation by 80 – 90%. Global radiation is defined as the total radiation, including the diffuse and direct radiation that reaches the Earth’s surface (Solar energy in McGraw-Hill Concise Encyclopedia of Science and Technology, 2004).
Extensive research is being carried on the utilization of solar energy; and the chief aim is to develop technology and discover efficient ways to capture the low-density solar energy, and convert it to a form that would be useful. In addition, forms of energy, such as wind energy, biomass energy, hydro power and thermal energy that derive from solar energy, promise to generate clean forms of energy. At present, with the sole exception of hydropower, none of these forms of energy are being employed to any significant extent (Solar energy in McGraw-Hill Concise Encyclopedia of Science and Technology, 2004).
Sources of energy that do not get exhausted and can be replenished are known as renewable sources of energy. Most of the renewable energy systems that are in use rely either directly or indirectly on solar energy. The direct sources include tapping the heat and light of the sun, whereas the indirect sources are wave power, hydroelectric power, and wind turbines (Renewable energy in Illustrated Dictionary of Science, Andromeda, 1988).
With growing awareness, regarding the ill effects and the limitations of fossil fuels, which will eventually be totally consumed, there is a sustained effort to change over to a more eco – friendly economy that is