An analytical study on optimal spectral characters of solar absorbing coating and thermal performance potential of solar power tower

The solar power tower (SPT) is one of the dominant applications of concentrating solar power technology. The tower receiver, as the core component of the SPT system, is responsible for solar absorption and conversion by virtue of the solar absorbing coating (SAC) deposited on the receiver surface. The SAC exerts a crucial role in the activity of the solar-thermal conversion process. However, the high nonuniformity of the solar flux and temperature distributions on the tower receiver, especially in the next-generation SPT systems, challenges the rationality of the SAC in terms of spectral selectivity characters. To explore the optimal spectral characters and tradeoff of radiation properties of the SAC, a spectral heat transfer model of the tower receiver is established and verified. The universal rules of the optimal cutoff wavelength of the ideal SAC varied with concentration ratios and temperatures are revealed. In addition, Dunhuang 10 MW SPT plant is selected to investigate the tradeoff mechanism between the solar absorptance and thermal emittance of the ideal SAC in practice and to evaluate its thermal performance potential. Furthermore, the impacts of solar irradiance, inlet temperature, and mass flow rate on the tower receiver are also studied. The results show that the optimal cutoff wavelength and spectral characters of the ideal SAC varied dramatically with the concentration ratio and surface temperature, revealing that the design principle for the advanced SAC used in the next-generation SPT should focus more on the thermal emittance other than the solar absorptance. The thermal efficiency of the Dunhuang tower receiver with the ideal SAC coating reaches 0.84, which is improved by 21.7 and 6.3% compared to the conventional tower receivers covered with black Pyromark paint and TaSi₂ multilayer coating.