Enhanced photovoltaic efficiency through radiative cooling augmented by a thermosyphon effect

A passive radiative cooling system that can produce cold water at night and act as an active cooling channel during the daytime is proposed to enhance the photovoltaic efficiency of a conventional PV module. At night, the PV module acts as a radiative cooling surface on which cold energy can be harnessed by passing water underneath the PV module. We show that a thermosyphon effect can circulate water in a closed-loop at night without any power consumption. On the other hand, the stored cold water can be fed through the water channel and cool the PV module during the daytime. A quasi-steady-state one-dimensional simulation code has been developed to analyze the annual performance of the proposed radiative-cooling-assisted PV module system. In this study, we have taken into account two parameters: the water mass (or water storage tank size), which ranges from 100 to 700 kg, and the insulation covering the storage tank, which ranges from no insulation to perfect insulation. By taking the total amount of water as the main design parameter of the proposed system, we show that it is beneficial to install a tank to hold more than 300 kg. Moreover, no insulation on the storage tank is found to be desirable for further enhancing the photovoltaic efficiency. It is also revealed that the efficiency enhancement is closely related to the climate conditions, in particular, the diurnal temperature range. Thorough analysis indicates that the proposed system is appropriate for hot, dry locations where the diurnal temperature range is relatively large. For example, the proposed system can enhance the net power output by 6.4% as compared to a conventional PV module in Phoenix. We think that the proposed radiative cooling system will be a great way to make conventional PV modules work more efficiently.