Colored absorbers for solar thermal collectors a numerical study for Lebanese buildings

Most flat plate thermal collectors have a black appearance which makes it difficult to building owners and architects to accept. The objective of this paper is to investigate the thermal impact of using different colors to coat the absorbers of solar thermal collectors integrated to the envelope of Lebanese buildings. The aim is to check the potential of alternative dark colors at the place of the black selective coating to produce the required energy, while gaining in aesthetical and technical integration. A selection of four dark colors is tested for different orientations and compared to a reference black collector. It has been shown that for grey and green absorbers, the loss of performance is not significant, and that increasing the collecting area by a factor of 2.2 these colored collectors can produce the same amount of the energy needed. This is a relatively acceptable ratio by considering that the area is largely available in the envelope, and that these collectors are multifunctional components, replacing some parts of the building envelope.