Abstract

Solar thermal, photovoltaic, and radiative cooling are the three main methods to harvest solar radiation and universe coldness for building energy conservation and carbon-emission reduction. In this regard, the hybrid solar photovoltaic/thermal (PV/T) system is especially favored because of its compact structure and high energy efficiency. However, most buildings have dynamic cooling and heating demands related to climate zones and seasonal fluctuations, which can compromise the year-round efficiency of single-mode devices (i.e. heating or cooling alone). Herein, a hybrid solar photovoltaic/thermal-radiative cooling system (PV/T-RC) was proposed for the dynamic thermal management of buildings by enabling the system to switch between heating and cooling modes according to seasonal weather changes while providing year-round renewable electricity for buildings. The PV/T-RC system consists of a PV/T module and an RC module that is distributed to the sunny and dark sides of the roof, respectively, to boost the heating, electricity, and cooling output. An inorganic geopolymer radiative cooling (IGRC) coating was synthesized to fabricate the RC module, which could achieve a solar reflectivity of 94.9% and broadband infrared thermal emissivity of 0.93. Theoretical analysis indicates that distributing the PV/T module and RC module on the south and north sides of the roof can effectively increase the year-round output of the heating/cooling energy and electricity. The field tests in Hong Kong showed that in the cooling mode, the RC module achieved a maximum daytime subambient cooling effect of 2.4 °C, which is 22.2 °C lower than that of the reference roof, and it reduced the indoor air temperature by 7.2 °C. While in the heating mode, the temperature of the PV/T module is 8.1 °C higher than that of the reference roof, increasing the indoor air temperature by 2.7 °C. The annual prediction results demonstrated that the PV/T-RC system can provide continuous heating, cooling, and electricity for buildings in regions with hot summers and cold winters.