Experimental study on a hybrid photo-thermal and radiative cooling collector using black acrylic paint as the panel coating

Radiative cooling is treated as a promising clean alternative for cooling energy harvesting by dissipating heat to the sky mainly at night in a passive manner. Yet the cooling flux of a stand-alone radiative cooling system is far below a conventional vapor compression refrigeration system, which hinders its wider application. If the nocturnal radiative cooling process acts as an auxiliary function of the solar collector, the aforementioned limitation of radiative cooling technique can be addressed. Therefore, a dual-functional collector which can offer heat in daytime and cooling energy in nighttime was proposed in this study. This hybrid photo-thermal and radiative cooling collector used the cheap and accessible black acrylic paint as the panel coating. A photo-thermal and radiative cooling prototype was manufactured and investigated experimentally in heating and cooling modes. Results showed that the thermal efficiency at zero-reduced temperature and cooling efficiency at zero-dimensionless temperature difference were 63.0% and 58.3%, respectively under clear sky condition. Besides, the collector achieved a net radiative cooling flux of 55.1 W/m2 in a clear night. Moreover, the hybrid system gathered a daily heat of 8.64 MJ during a consecutive 8 h, and a nightly cooling energy of 0.99 MJ in a consecutive 11.5 h.