Negative thermal-flux phenomenon and regional solar absorbing coating improvement strategy for the next-generation solar power tower

Solar power tower (SPT) is regarded as the most promising technology for applications in concentrating solar power. However, a significant decrease in the solar-thermal conversion efficiency of the tower receiver in the SPT system occurs at high operating temperatures due to the massive radiation heat loss caused. In this work, a detailed heat transfer model of the tower receiver was established, and the negative thermal-flux phenomenon was discovered in the tower receiver based on the verified simulation results. In this context, a novel improvement strategy for regional solar absorbing coating on the tower receiver was proposed to enhance the thermal performance of the tower receiver in the next-generation SPT system. Two kinds of novel tower receivers by changing conventional solar absorbing coating into the silver-based coating (novel receiver I) and black chrome-based coating (novel receiver II) at negative thermal-flux regions were proposed, investigated, and compared with the prototype tower receiver without changes. The overall thermal performance of three kinds of tower receivers was numerically analyzed under different solar irradiances, solar hours throughout the day, and seasons. The results demonstrated that both the novel tower receivers achieved breakthrough enhancements on the thermal performance compared with the prototype receiver, showing great potential for practical application. The negative thermal-flux regions accounted for almost a quarter of the entire receiver surface. The annual average radiation heat losses from negative thermal-flux regions in the novel receivers I and II were effectively reduced by 93.00 and 53.14%. Accordingly, the annual average heat gains and receiver efficiencies were significantly enhanced by 6.54 and 6.03%, respectively.