Solar collectors

The central element of a solar thermal system is the collector. This consists of an absorber, a cover (usually made of glass) and a frame with thermal insulation.

Figure 4: Design of a flat plate collector (Source: http://de.wikipedia.org/w/index.php?title=Datei:Sonnenlichtkollektor.png&filetimestamp=20040725145740)

The absorber has the function of absorbing solar energy and converting it into heat. The performance and efficiency depend on the properties of the absorber.
In flat-plate collectors, the absorber consists of metal strips or a full-surface metal sheet, which are selectively coated. The so-called selective coating ensures that the absorber effectively absorbs certain wavelengths, i.e. short-wave solar radiation, and on the other hand that long-wave thermal radiation in the infrared range is emitted again to the lowest possible extent.

The degree of absorption indicates how much solar radiation is absorbed, the degree of emission indicates the proportion of thermal radiation that is emitted again.

Up to 95% of solar radiation can be absorbed by selectively coated absorbers, while only up to about 5% of thermal radiation is emitted (emissivity).

The most common materials for the absorber are copper and aluminium. Aluminium has only been increasingly used again since the price of copper rose. The problem with the use of aluminium is that “mixed installations” occur between copper pipes and aluminium sheet and undesirable chemical reactions can occur. In these cases, special heat transfer media must be used.

Disclaimer: Powered by Erasmus+, ACTeco, ASBN and d.sign Gruber & Partner