Solar Thermal

At the heart of a solar thermal system is the solar collector.

There are a number of different design concepts for solar collectors; the majority that are sold in Europe are of the flat-plate type.

The main components of this kind of flat-plate collector are a transparent front cover, collector housing and an absorber. The absorber, located inside the flat-plate collector housing, converts sun’s radiation into heat, while fluid circulating through the attached tubes carries the heat away where it can be used or stored.

Highly efficient absorbers are usually coated with dark selective coatings, i.e. black chrome, black nickel, or titanium nitride oxide, which reduce radiation heat losses. This makes it possible to absorb and transform a large part of the short-wave solar radiation into heat, and, simultaneously, the emission of the long-wave heat radiation from the absorber itself is significantly reduced. Usually, 95% of the irradiated solar radiation can be absorbed and converted into heat.

The heated fluid is pumped to a heat exchanger, which can be a coil in the storage vessel or an external heat exchanger where it gives off its heat and is then circulated back to the panel to be reheated.

As the collector can reach stagnation temperatures up to 200°C (i.e. when no water flows through), all the materials used must be able to resist such heat. Therefore, the absorber is usually made of metal materials such as copper.