Metal/insulator composite selective absorbers

The optical properties of metal/insulator composite films have been examined, and their utilization as solar selective absorbers studied both theoretically and experimentally. Calculations have been made on the solar selective performance of graded composite films, demonstrating the performance and limitations to be expected for the general class of composite film absorbers. Design guidelines for the fabrication of optimum selective absorbers have been developed and subsequently implemented in the construction of selective absorbers using two promising composite materials, Ni/Al₂O₃ and Pt/Al₂O₃. Measurements of reflectance, solar absorptivity α, thermal emissivity ε and high temperature durability have been made. The results show values of α≥0.94 for both Ni and Pt composite films. Values of α/ε 1 ̌3 at 150°C were obtained for both composite materials when deposited on Cu substrates. A selectively absorbing film has been produced which shows no change in performance parameters after extended heating at 600°C in air.