Performance Enhancement of Solar Absorber Coatings by an Antireflective Nanostructured Layer

Inspired by a multi-layer coral-structured absorber coating developed by Nano Frontier Technology (NFT), we propose an antireflective nanostructured layer or “top layer” comprised of a large number of silica nanospheres (~120 nm in diameter) and an adhesive silica matrix (~8 nm in thickness) that can be applied to an existing solar absorber coating to improve its sunlight absorption and durability. For a coral structured coating, the top layer improved the sunlight absorption (solar-weighted absorptance) by more than 1% after ageing for 1000 h at 900°C, while the improvement was 0.4% when it was in its pristine condition. For a Pyromark 2500 coating, which is considered the gold standard in the concentrating solar power (CSP) industry, the improvement of adding the top layer was 0.8% in its pristine condition and 0.25% after ageing for 1000 h at 800°C. Based on the difference in morphology and material properties between the NFT and Pyromark coatings, our results indicate that the improvement from applying the top layer depends on the characteristics of the underlying material. The results are promising for the CSP industry, as they indicate that any solar absorber coating may be upgraded in performance without modifying their original composition, morphology and deposition method. Importantly, there is the potential to apply a top layer to an existing coated receiver to boost its optical performance.