Reactively sputtered coatings on architectural glazing for coloured active solar thermal façades

Covering a standard solar thermal collector with a coloured glazing, which is opaque to the human eye but highly transparent to solar energy, permits a perfect architectural integration of solar panels into glazed building façades. The colours are based on interference in the thin-film coating on the reverse side of the glass. Coloured thin-film filters with optimised energetic performance and angular stability in their coloured reflection were deposited by reactive magnetron sputtering. For substrates up to 100 mm in diameter the geometric configuration of the deposition chamber and the process parameters were optimised. The optical properties of the coatings were determined by spectroscopic ellipsometry and spectrophotometry. Furthermore, by means of a window test bench, the CIELAB colour coordinates of real-size glasses were determined as a function of the viewing angle. It was also demonstrated that the colour of solar collector glazing can be matched to colours of commercial windows. In comparison to uncoated glass panels, the presented coloured samples for solar thermal panels have an energy loss of only 2.8–4.5% at normal solar incidence. This difference reduces for higher angles of incidence. Thus, taking into account the angular distribution of solar radiation, the energetic losses are even lower.