Concentrated solar power tower systems coupled locally with spectrally selective coatings for enhancement of solar-thermal conversion and economic performance

Tower receivers in next-generation concentrated solar power towers (SPTs) face an increasing challenge to suppress the massive radiation heat loss associated with an elevated operating temperature. Negative thermal-flux regions (NTRs) exist in tower receivers owing to the high but uneven temperature and solar concentration ratio on their surfaces. Spectrally selective coatings on NTRs are proposed in this study to reduce the radiation heat loss and thus improve the solar-thermal conversion efficiency of tower receivers. Four coatings, namely, black Cr, Ag film, and ideal coatings with cutoff wavelengths of 2.5 and 1.5 μm, are investigated to evaluate the compatibility and effectiveness of coatings with diverse spectral selectivities to improve NTR solar-thermal conversion performance. The Dunhuang 10 MWe SPT plant using a binary salt as the heat transfer fluid was selected for the study. A novel spectral heat transfer model of the tower receiver and an economic assessment model of the Dunhuang SPT plant were established and verified by the experimental results. These results showed that the spectral coatings locally coupled on NTRs were effective in regulating NTR radiation properties and reducing radiation heat loss, thus improving the thermal performance of the tower receiver. The tower receiver efficiencies with Ag and ideal coating (cutoff wavelength of 1.5 μm) were significantly improved by 6.92% and 12.03%, respectively, compared to that of a prototype receiver. The novel receiver based Dunhuang SPT plant harvested an annual power output improvement of 5.8% and levelized cost of energy reduction of 5.6%.