Preliminary thermal analysis of a combined photovoltaic-photothermic-nocturnal radiative cooling system

A novel combined photovoltaic-photothermic-nocturnal radiative cooling (PV-PT-RC) system was proposed to achieve multifunctional and all-weather operation. The proposed system collects electricity and heat energy at daytime through PV and PT conversions and cooling energy at nighttime through RC. A quasi-steady-state mathematical model that considers the spectral radiant distribution was established. A sensitivity analysis of the model to key inputs was carried out as well. An experimental apparatus was used to test the daily solar heating and nocturnal RC performance of the system, as well as verify the correctness of the mathematical model. The equilibrium temperature of the collecting plate showed root-mean-square deviation results of 2.8% and 1.8% in daily and nocturnal operation modes respectively, thereby validating the mathematical model. Simulation studies were performed to investigate the cooling performance of the PV-PT-RC system using the validated model. Results showed that insulation thickness and ambient temperature positively affects cooling performance, whereas wind velocity and precipitable water vapor amount negatively affects cooling performance. The RC performances of the PV-PT-RC system in different Chinese cities were investigated. The system exhibited optimal cooling performance during winter in northwestern China and the weakest cooling performance during summer in southeastern China.