High-quality absorbers have a special surface finish which absorbs the maximum amount of sunshine (up to 96%) and which itself radiates only the minimum amount of heat.
Researchers at BUT have developed a new type of solar absorber (utility model) which employs a specially shaped surface. As stated by one of the inventors, RNDr. Libor Mrňa, Ph.D., this solar absorber with a shaped surface is based on the idea of absorbing incident radiation in appropriately shaped structures created on the absorbing surface. The increase in absorption uses the effect of multiple reflections on the collector profiles and the gradual absorption of sunshine in cavities made across the surface. This effect also eliminates the requirement for the perpendicular incidence of radiation on the collector, since oblique incidence of the sun’s rays reflects radiation into the cavity where it is absorbed.
In addition, the structured surface increases the heat-exchange area between the absorbing surface and the transferring liquid medium inside the collector. Cavities – profiles in the absorbing surface - are made using methods for cold forming sheet metal, and the whole surface is equipped with a suitable absorption layer to enhance the effect of multiple reflections.
Fig. 1: Diagram showing the solar absorber function (Author: RNDr. Libor Mrňa, PhD.)
Možné směry dopadu slunečního záření - Possible angles of incidence, Solární absorbér - Solar absorber,
Teplosměnné médium - Heat-exchange medium
The main advantage of the solar absorber with a shaped surface compared to current types of absorbers is their greater efficiency irrespective of the direction of solar radiation, the low production costs and long useful life of the material. Current solar absorbers require perpendicular incidence to achieve the maximum effect of absorption. In most cases, they also need to be assembled obliquely, which may be architecturally problematic and technically more difficult to realize.
The potential use of solar absorbers with a shaped surface is very wide; the best known application is transforming sunshine into heat when heating water or buildings.
