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Solar collector - structure and functionA collector is a "catcher and collector". He collects the "collection". A solar collector therefore captures the sun and collects its energy. But a solar collector is not picky.
Namely, he collects a whole spectrum of frequencies of the sun's rays, in order to convert these into long-wave Stralung. This long-wave radiation is the heat.
Function of a solar collector
First of all, it lets the rays hit the absorber through a transparent surface (glass). Depending on the surface structure, it converts the wavelength of the radiation. So that the longer waves, the heat, does not escape again, the collector is insulated on all other sides. The glass, which does not pass through so much longer wavelengths, also impedes the "collection" from escaping from the collector. Ideally, there is a vacuum between the glass surface and the absorber. This almost completely eliminates heat loss. The medium-carrying pipelines absorb the heat and transport it to their intended use.
What types of absorbers are there?
The cheapest absorbers are installed in flat plate collectors. Small copper wires pass through the collector in front of a black surface. As the solar medium passes through the pipes, it is warmed up in this way by the heat of the flat surface. Flat plate collectors have a large surface area. The rays do not necessarily impinge perpendicularly. The efficiency is but at a perpendicular to the sun
lying surface best. Flat collectors are available in the version with or without vacuum.
Tube absorbers have a tube as absorber. This can be directly flowed through or give off its heat via a heat exchanger at the top of the collector.
Through the tube, a vacuum can be kept very good. Therefore, tube absorbers are often used in vacuum tube collectors. The evacuated tube collectors have parabolic bent metal sheets on the underside, which reflect the sun's rays onto the absorber, depending on the angle of incidence. The efficiency increases greatly.
If no liquid medium, but a gaseous medium for heating or heat removal from the collector is used, one speaks of air absorbers. That these are not operated with a vacuum is self-evident. Air absorbers are often used for premises with high altitude. They can be integrated into the façade with skilful architecture. This solution is extremely rare.
Function of collectors
Concentrating collectors direct the radiation onto an absorber tube via a large parabolic mirror. This technique is used in industrial applications for the operation of steam processes and the like. In this way, electricity for several tens of thousands of households is already being produced in sunny regions. This type of collector is fundamentally different in structure from the photovoltaic and can therefore not be compared with it.
What color do solar panels have?
If we wear a black shirt and stand in the sun, we know that in this way solar energy can be well absorbed. One speaks of absorption. Therefore, the first solar panels were rather black. However, the heat is released again. This emission can be optimized. The more modern solar panels shimmer therefore rather bluish. These coatings have the advantage that they - similar to the black coating - absorb the radiation well, but also have a lower emission of heat. The power density of the collectors thereby increases.