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Solar power






The Sun's energy manifests itself as thermal, photoelectric and photochemical effects. Men have tried to use solar energy since earliest times, but no means existed to generate useful power from the Sun's heat until steam and hot-air engines were invented.

Crude devices for heating water by solar energy date back many years, and production of salt by solar evaporation of sea water is probably the most ancient of man's sun-activated processes. Photo­electricity has been known for almost a century, and millions of selenium photocells have been used as light meters and in similar application.

Most fundamental of all thermal solar processes is the simple fact that, when sunlight falls upon a surface of any kind, the surface becomes warmer than the surrounding air. The extentrise of the surface temperature depends upon many factors. The most important of which are the angle between the surface and the sun's rays, the absorptivityof the surface and precautionstaken to prevent the surface from losing the absorbed heat.

The angle effect is caused by the fact that the Sun's rays travel in straight lines. When a surface is perpendicular to the rays, their intensity is at its maximum; the surface being horizontal, the radiation intensity drops off and reaches its minimum.

The most effective way to minimize the loss of energy from the heated surface is to Cover it with one or more sheets of a glass-like material. This material is transparent to the Sun's rays but opaqueto the longer wave length emitted by the warmed surface. The air space between the surface and the glass is an effective prevention of heat loss by convection.

A flat plate of blackened metal covered with one or more transparent sheets of glass or plastic is known to be the simplest collector of solar energy. Once collected, heat can be used in a variety of ways. Here are some of the potential and actual applications.

Space heating is probably the most important, since nearly one-third of our energy supply is used for this purpose. Water heating can be achieved by portable solar heaters, which are able to give as much as 400 litres of boiling water on a sunny day.

The distillation of sea's water is another process to be accomplished by variations of the simple plate collector. The production of temperatures low enough for air conditioning and domestic refrigeration is a very important potential use of solar energy which is only now beginning to receive the attention it deserves.


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