Optical Overheating Protection
With all solar thermal collector systems there is a potential risk that the solar collector may reach an equilibrium or stagnation temperature higher than the maximum safe operating temperature. Various measures are taken for optical overheating protection. Stagnation temperatures are encountered under conditions of high radiation while no heat transfer fluid is flowing through the collector, for example during power failures, component failures, servicing, energy storage capacity limitations, or periods when little hot water is extracted from the system. More generally, stagnation conditions can be considered to be any situation under which the solar collector cannot adequately dispatch the absorbed solar heat to the heat transfer fluid. Besides any damaging effects to the system, high stagnation temperatures also place constraints on collector materials. These materials must retain their important properties during and after exposure to the high stagnation temperatures. This imp ...
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Solar Thermal Collector
A solar thermal collector collects heat by Absorption (optics), absorbing sunlight. The term "solar collector" commonly refers to a device for solar hot water panel, solar hot water heating, but may refer to large power generating installations such as solar parabolic troughs and Solar power tower, solar towers or non-water heating devices such as solar cookers or solar air heaters. Solar thermal collectors are either non-concentrating or concentrating. In non-concentrating collectors, the aperture area (i.e., the area that receives the solar radiation) is roughly the same as the absorber area (i.e., the area absorbing the radiation). A common example of such a system is a metal plate that is painted a dark color to maximize the absorption of sunlight. The energy is then collected by cooling the plate with a working fluid, often water or glycol running in pipes attached to the plate. Concentrating collectors have a much larger aperture than the absorber area. The aperture is ty ...
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