Field investigation of a hybrid photovoltaic-photothermic-radiative cooling system

Radiative cooling (RC) is a passive and green cooling technique dissipating heat to outer space, which is a natural heat sink. Yet most available radiative coolers are encountered with the challenges of low power density and daytime operating ability. In the meantime, solar photovoltaic/thermal (PV/T) collectors cannot work at night. To overcome this limitation, the present work proposed, designed and manufactured a practical-scale photovoltaic-photothermic-radiative cooling (PV-PT-RC) collector. The hybrid PV-PT-RC collector is capable of generating electricity and heat during the day and providing cooling energy at night. Subsequently, to study the performance of the collector, we developed an outdoor experimental system and performed experiments at various operation modes. As results suggest, the average electrical efficiency of the collector around noon was 10.3% and showed thermal efficiency at zero-reduced temperature of 55.3% in a diurnal collector mode test. The net RC powers of the collector in a clear night and overcast night reached 72.0 and 30.8 W/m2, respectively. Multi-day daily system mode tests were performed, and the results suggest that the overall electrical/thermal efficiency of the PV-PT-RC system was ranged from 40.4% to 56.9%. The overall cooling energy gain of 2.90 MJ was obtained by the system at a typical clear night. The tri-functional collector is expected to provide indispensable electricity, heat as well as cooling energy in building and agriculture fields.