Before 1700 A.D. most of the power available to human society was limited to solar energy trapped by green plants which produced organic matter. It was the biological oxidation of this organic matter which fuelled the muscle power while combustion of organic matter provided energy for other purposes such as lighting, cooking, heating etc. The formation of fossil fuels (coal, oil and natural gas) is also due to photosynthesis carried on by plants which occurred? Millions of years ago. These were, however, not in general use before the beginning of Industrial Revolution. Energy requirements of man were modest and could be fulfilled by solar energy 'recently' fixed by green plants. The situation has now changed drastically.