Photothermal testing before and after degradation of nickel-pigmented aluminium oxide selective absorber prepared by alternate and reverse periodic plating technique

The alternate and reverse periodic plating techniques were used to prepare the selective absorber samples. The glazed type-flat plate collector was used for photothermal testing. The calculated absorptivity of the selective absorbers (before degradation) falls in the range 92.0–97.0% and after degradation falls in the range 88.3–92.2%; while emissivity (before degradation) falls in the range 11.0–22.5% and after degradation falls in the range 11.6–23.4%. The maximum calculated net collective flux (before degradation) is in the range 590–699 W/m−2 and after degradation is in the range 566.4–664.1 W/m−2. The conversion efficiency (before degradation) is in the range 0.73–0.78 and after degradation falls in the range 0.70–0.74. Degradation testing carried out in air at different temperatures: 100 °C, 200 °C, 250 °C, and 300 °C. The degradation process leads to a decrease in the solar absorptivity and increase in the thermal emissivity of the films especially at 300 °C. Different parameters are discussed concerning the photothermal and the degradation testing.