PHOTOTHERMAL CONVERSION OF SOLAR-ENERGY BY GOLD CERMET COATINGS - APPLICABILITY OF THE BRUGGEMAN EFFECTIVE MEDIUM THEORY

Efficient photothermal conversion of solar energy requires high absorption at wavelengths λ≲2 μm and low absorption at λ≳2 μm. This absorptance profile can be achieved by coatings consisting of ultrafine metal particles in an insulating matrix. I compare available optical data for concentrated gold cermet films with calculations based on the non-self-consistent Maxwell Garnett theory and on the self-consistent Bruggeman theory. The latter is found to be superior for MgO+25 vol% Au and for Al 2O3+18 vol% Au, whereas no firm conclusions can be drawn for MgF2+Au.