Investigation on a novel integrated system of radiative cooling and solar photovoltaics

Daytime radiative cooling relies on a high reflectivity in the solar spectrum and a high emissivity in the atmospheric window spectrum. However, the reflected solar radiation, as a high-quality energy, is wasted. Based on the incident solar radiation primarily concentrated at a specific angle and the emitter's hemispherical heat exchange with space, it is possible to collect it. There has been no work to date that collects the substantial energy reflected by the emitter yet. Here, an idea of enhancing solar power generation during the daytime while ensuring day-and-night radiative cooling was proposed in this work. It is indicated that the emitter with only five layers can achieve a weighted average reflectivity of 95.22 % in the solar spectrum and a weighted average emissivity of 94.74 % in the atmospheric window spectrum. Outdoor experiments show that the average temperature reduction from 10:30 AM to 3:30 PM is 2.3 °C, which can further decrease to 8.4 °C from 3:30 PM to 8:00 PM. Under direct sunlight, the maximum output power density of the solar cell is 125.5 W/m2, which can be enhanced to 163.5 W/m2 by aligning the orientation of the solar cell with the emitter using a simple angle controller, representing a remarkable enhancement of 30.3 %. Finally, through simulations on a 5.4 × 4.4 × 3.4 m3 communication base station, it is determined that without convective losses, the chamber temperature reduction is 11.7 K, and the generated power can be as high as 169.4 W/m2 from the portion reflected by the emitter and 177.9 W/m2 from the portion directly from the sun. The results highlight the great potential for the commercial application of combining radiative cooling with a photovoltaic system.