Spectrally selective solar absorbers in different non-black colours

Silicon paints were prepared from yellow, ochre, dark ochre, green and blue pigments. To improve the solar absorptance, as, of these coatings, an existing black paint was admixed in different ratios. The optical properties of the mixed paints thus formed are expressed in terms of the Kubelka–Munk absorption and scattering coefficients in the spectral region 400–17000 nm. The scattering coefficient obtained for all paints was essentially equal. In the visible region the absorption coefficient follows the spectral characteristics of each respective colour. In the infrared absorption at ∼9000 nm and above 12000 nm are seen in all cases which result in a thickness-dependent increase of the thermal emittance, eT, of the coating. The metric chroma (Cab*) and lightness (L*) in CIELAB colour space were calculated for wide-angle observer in average daylight conditions. A range of non-black spectrally selective solar absorber surfaces with as>0.8 and eT<0.3 have been prepared with L*<45 and Cab*<10.