Solar heat has been used since times immemorial for drying of foodstuff like grains and fish, and for extracting salt from seawater near seacoast. Solar thermal energy refers to the utilization of solar energy by capturing the available solar radiation and transferring it as heat perform various useful activities, like, heating, cooling, drying, water purification, industrial process heat and power generation. The first deliberate attempt to make the Sun do some work for humans is reported from about 2,000 years ago. Like many useful inventions it was the result of a war. It is said that in 212 BCE, when the Romans attack Greeks, The Greeks scientist Archimedes was able to set fire to the Roman ships at Syracuse by focussing sunlight reflected from mirrors set in circullar arc. This idea remains domants for 1800 years. But in the 17th, 18th, 19th, ceturies several scientists in Europe made attempts to melt metals by focussing Sunlight by means of large convex lenses and concave mirrors. All metal including silver, gold, copper, and even platinum having a melting point at 1769 degree celcious were melted in this fashion. These were mostly scientific experiments, exception being a solar furnace built by famous steel make Bessemer. His furnace had diameter of 3 metres in which he melted copper and zinc in 1868.
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