Black surfaces are particularly good at absorbing shortwave radiation of light and then converting it into heat. This physical property is used in the so-called absorbers. These are made from plastic or metal in the form of panels, mats, or pipes with a black surface which, depending on the quality of the absorber, is voltaic or otherwise finished. Abosrbers are the active part of a solar system. Depending on the scenario and the level of the required temperature, a distinction is made between:
Absorber systems are not insulated or covered. The heat transfer medium flows directly through them. These are structually simple, affordable systems suitable for operating temperatures below 40° C. Their primary areas of application are heating swimming pool water and preheating service water.
Absorber mats, usually made from plastic, can be placed on flat or slightly inclined roofs, also retrospectively, with little construction work.
Collector systems with flat plate collectors contain an absorber (typically in metal) in a sealed housing fitted with a transparent cover and heat insulation on the rear side. The transparent covering reduces irradiation from the absorber to the environment, while the thermal insulation reduces heat losses on the rear side, enabling temperatures of over 150° C to be reached. Primary areas of use are in water heating and space heating. Flat plate collectors are available in various sizes from 1 to 10 m². Special designs (e.g. triangular) are also possible. They are integrated within the roof cladding in prefabricated modules or attached to the roof cladding and interconnected.
Evacuated tube collectors contain a metal absorber sealed in evacuated glass tubes. The vacuum ensures that heat losses are kept to a minimum, enabling temperatures of over 200° C to be reached. Areas of use are heating service water, space heating, and generating process heat, as well as solar cooling of buildings.