Angle-dependent spectrophotometry of Sol-Gel deposited multilayered oxide coatings on solar collector glasses

Multilayered thin oxide films have been deposited on solar collector glazing by sol-gel dip coating in a dust-free environment provided by a laminar flux chapel. A superior film quality and a satisfying film homogeneity have been achieved for the produced coatings which are nearly completely free of visible point defects. The thicknesses of the individual layers are determined by a numerical analysis of angle-dependent spectral transmittance data. The visible reflectance RVIS, and the CIE color coordinates for the multilayer stacks have been inferred from spectral reflectance data as functions of the angle of reflection. The angle-dependent solar transmission Tsol has been measured directly by a solar simulator in combination with a thermopile detector. The energy efficiency of the visible reflection M = RVIS/(100% Tsol) can thus be determined as a function of the incident angle. The produced coatings combine a bright colored reflection with an acceptable solar transmittance, and are thus well suited for the application in colored glazed thermal solar collectors. This novel type of colored glazing opens up new perspectives for the architectural integration of thermal solar collectors, e.g. as solar active glass facades.