Effect of sand soiling on the performance of high-temperature solar absorber coatings

Concentrating solar power (CSP) is a renewable energy technology that converts concentrated sunlight into thermal energy. Central-receiver (solar-tower) systems are a CSP configuration whose efficiency and longevity depend on the performance of solar absorber coatings. These coatings degrade due to various factors, including soiling from sandstorms in desert environments that reduce their solar absorptance. This study investigates the impact of severe artificial soiling on the optical degradation of two types of coatings: Pyromark 2500 and a hierarchical coral-structured coating. To achieve this, the coatings were exposed to 50 mg of China sand dust, a standard sand deposited on the coating as a contaminant. Their absorptance, chemical composition and morphological changes were analysed before and after 400 h of ageing at 800 and 900 °C. The results indicate that the extent of the sand coverage influences absorptance degradation, which is more pronounced in the coral-structured coatings as the sand particles fill the gap between macro-scale protrusions, reducing the light-trapping performance induced by multiple reflections. Furthermore, the effect of temperature on absorptance degradation is less significant at 900 °C due to the likely structural changes in sand dust at higher temperatures. This work elucidates the impact of sand soiling on the performance of both conventional and advanced solar absorber coatings. • Sand dust impacts light-trapping efficiency in solar absorber coatings. • Sand soiling reduces solar absorptance in CSP coatings by up to 10%. • Coral-structured coatings degrade more with sand coverage than Pyromark 2500. • Solar absorptance increases initially at 900 °C due to sand structural changes.