Abstract :
The architectural integration of thermal solar collectors into buildings is often limited by their black color and the
visibility of tubes and corrugations of the absorber sheets. A certain freedom in color choice would be desirable, but the
colored appearance should not cause excessive energy losses. Multilayered interference filters on the collector glazing
can produce a colored reflection, hiding the corrugated metal sheet, while transmitting the non-reflected radiation
entirely to the absorber. We investigate the potential of quarterwave stacks by simulation of their optical behavior,
yielding the visible reflectance RVIS, the solar transmittance Tsol, a figure of merit M = RVIS/Rsol, and the CIE color
coordinates. The necessary number of individual layers in the multilayer stack as well as the choice of refractive indices
and thus of thin film materials are discussed. Finally, examples for realistic multilayer designs are proposed.
2005 Elsevier Ltd. All rights reserved
