Performance evaluation and durability studies of W/WAlSiN/SiON/SiO2 based spectrally selective solar absorber coating for high-temperature applications: A comprehensive study on thermal and solar accelerated ageing

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We report a solar selective coating of W/WAlSiN/SiON/SiO2 fabricated using a Four-Cathode Reactive Unbalanced Direct Current (DC) magnetron sputtering system with high thermal stability, good durability and resistance to outdoor testing conditions. The coating also exhibits superior mechanical properties (Hardness ∼12 GPa). In addition, thermal shock tests at high temperatures and solar accelerated ageing measurements are investigated in-depth to analyze the performance of the solar absorber coating. The thermal shock tests of the samples at various temperatures in the range of 500–600 °C depict the excellent thermophysical resistance of the as-deposited samples. To test the thermal durability of the solar absorber coating, we applied 200 cycles of solar accelerated ageing on the samples using a solar accelerated ageing facility with concentrated flux density varying from 50 to 250 kW/m2. These cycles have been defined to replicate real high solar flux and temperature on the front side of the samples along with high cooling and heating rates, reproducing the abrupt variations of solar irradiation due to cloudy weather and subsequent thermal shocks for a given receiver. Overall, the durability tests of the solar absorber carried out under various conditions indicate a minimal change in the optical properties (Δα = 0.002 and Δε = 0), thus, making it a potential candidate for high-temperature solar thermal applications.