Spectral optimization of solar selective absorbing coating for parabolic trough receiver

Abstract

Solar selective absorbing coatings that absorb solar irradiation and emit infrared radiation have a significant impact on the thermal efficiency of the receivers. The spectrum parameters heat transfer model and the non-ideal coating curve model are established. The cutoff wavelength of coatings is comprehensively optimized, and the effect of the optical properties of the coating on overall performance is analyzed. Results show that the optimal cutoff wavelength rises with the solar irradiation flux but decreases with increased absorber temperature. Sensitivity analysis results of the coating optical properties indicates that the thermal efficiency significantly decreases with increasing slope width. The change range of the thermal efficiency at the temperature of 200 °C is ±0.1%, resulting from a ±1 μm variation in slope width, whereas the range at 600 °C is ±6.5%. Spectral absorptivity analysis shows that the coating absorptivity has nearly same positive influence on thermal efficiency under different temperatures and irradiation fluxes, whereas emissivity analysis reveals an evidently different negative effect on the receiver performance. Finally, the annual optimal cutoff wavelength decreases with increasing temperature but increases with solar irradiation. The optimal cutoff wavelength decreases from 2.23 μm at 200 °C to 0.78 μm at 600 °C in Phoenix.