Design And Optimization Of Nanoparticle-Pigmented Solar Selective Absorber Coatings For High-Temperature Concentrating Solar Thermal Systems

We present a systematic approach for the design and optimization of nanoparticle-pigmented solar selective absorbers for operation at 750 degrees C. Using the scattering and absorption cross-sections calculated by Lorenz-Mie scattering theory as input, we employ a four-flux radiative transfer method to investigate the solar selectivity mechanism and optimize the optical-to-thermal conversion efficiency (eta(therm)) as a function of the metallic nanoparticle material, the nanoparticle diameter, the volume fraction, and the coating thickness. Among the nanoparticle material candidates in this study, C54-TiSi2 is the best option with an optimized eta(therm) = 87.0% for a solar concentration ratio of C = 100 and eta(therm) = 94.4% for C = 1000 at 750 degrees C. NiSi is also a promising candidate comparable to TiSi2 in thermal efficiency. Experimentally, an un-optimized 200 nm-diameter TiSi2 nanoparticle-silicone solar selective coating has already achieved eta(therm) = 89.8% for C = 1000 at 750 degrees C. This performance is consistent with the theoretical model and close to the thermal efficiency of the commercial Pyromark 2500 coatings (90.1%). We also demonstrate that Ni/NiSi core-shell structures embedded in the SiO1.5 matrix is thermally stable at 750 degrees C for 1000 h in air. These results indicate that silicide cermet coatings are promising to achieve high optical performance and high temperature thermal stability simultaneously. Published by AIP Publishing.