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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 early times, but no means existed to generate useful power from the Sun’s heat until steam and hot air engines were invented. Grude devices for heating water by solar energy date back many years, and production of salt by solar evaporation of seawater is probably the most ancient of man’s sun-activated processes. Photo-electricity has been known for almost a century, and millions of selenium photocells have been used as light meters and in similar applications.
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 extent rise of the surface temperature depends upon many factors. The most of which are the angle between the surface and the sun’s rays, the absorptivity of the surface and precautions taken 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 opaque to the longer wavelength emitted by the warmed surface. The air space between the surface and the glass is an effective prevention of heat loss by convection. (by A.Kovalenko)
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What is the most ancient of man’s sun-activated processes?
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When does the surface become warmer than the surrounding air?
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Men have tried to use solar energy since______
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The ____is caused by the fact that the Sun’s rays travel in straight lines
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The air space between the surface and the glass is an effective prevention of_______
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