Directionally selective dielectric structures for solar radiation control

Abstract Windows represent a primary approach for direct indoor use of solar energy in terms of lighting and heating if differentiated radiation control ensures continuous visual and thermal comfort. Total internal reflection is a well known phenomenon that can fulfil directionally selective tasks covering most of the solar spectrum without absorption. Promising designs of dielectric structures are presented together with performance results from two-dimensional ray-tracing. Dynamic solar control systems based on rotatable slats can be modified in two ways. The first design complements state of the art prismatic structures in order to provide partial transparency of the material itself. A new approach rearranges the reflective segments in a way that enables total internal retro-reflection. The spacing between adjacent slats for unobstructed view can be increased for selected solar profile angles. For stationary solar control, cylindrical shells have been devised that can totally reflect a broad range of incoming rays. The new design removes the constraint on total reflectance aperture angle exhibited by prismatic geometry. Seasonal solar control on vertical southern facades can be achieved with a structure that reflects light only from high elevation angles and is partly transparent in other directions.