3.0 Renewable energy sources
Renewable energy is a flow of energy, that is not exhausted by being used. The primary renewable energy source on earth is solar radiation. The total flow of solar energy through earth's natural system is some 10,000 times greater than the present flow of energy through man's machines. Even the one per cent of the solar influx that generates the great atmospheric pressure systems which drive the winds, and which in turn generates the waves, in some 180 times as large as man's rate of energy use. And though, on the average, the photosynthetic process is less than 0.2 per cent efficient, even photosynthetic production creates 10 times as much energy as man uses.
The flow of solar and solar derived energy forms is not independent from the activities of man. The radiation fluxes are modified by changing the reflectivity of earth surface, examples by urbanisation, agricultural practices, deforestation. Man's activity also change wind patterns and modify cloud coverage. Injection of pollution in to the environment, removal of forest cover as well as man made structural changes, influences both radiation, heat and water flows (Carlsmith et al 1990 and Fulkerson et al 1989).
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