High temperature stable solar selective coatings by cathodic arc PVD for heat collecting elements

• Cr/CrTiAlN-G/TiAlN/AlSiN/AlSiO solar selective coating for SS heat collecting tubes.
• The achieved absorptivity and thermal emissivity values are: 0.959 and 0.09.
• High temperature stability up to 500 °C.
• Highly reproducible and promising for commercial exploitation.

A functionally multilayered Cr/CrTiAlN-G/TiAlN/AlSiN/AlSiO coating configuration, suitable for enhancing solar selectivity of stainless steel substrates used in concentrated solar power (CSP) systems, has been formulated using cathodic arc physical vapor deposition (CAPVD) technique. The sequence of functional layers was decided based on their refractive index values and their relative thickness was optimized to achieve maximum solar selectivity. The optimized coating exhibits encouraging values of solar absorptivity (α) – 0.95 and thermal emissivity (ε) – 0.09 to 0.14 up to 600 °C. Further, the solar selectivity factor (α/ε) for the coating is found to be comparable with the best selective coatings currently available for elevated temperature operation. The coatings were also studied for their long term stability and found to be stable up to 500 °C, although considerable change in optical properties was observed on increasing the temperature to 600 °C. The noted properties make the present coating a promising candidate as a high temperature solar selective coating on stainless steel substrates.