Experimental study on a direct water heating PV-T technology

This paper details a field study and a theoretical model of a PhotoVoltaic-Thermal (PV-T) system consisting of a solar PV panel with a thermally insulated water reservoir underneath. Unlike conventional PV-T systems, water is in direct contact with the glass solar PV panel. Thus, metallic tubular heat exchangers are omitted in this design. During operation, the PV-T panel is tilted, and cold water is pumped into the reservoir from the side closest to the ground. This achieves an active cooling of the PV panel maintaining an optimal electrical efficiency. Generated electricity is used to operate pumps and run the control system, while excess electricity is stored in a battery to be utilised as desired. The system and the inlet water absorb solar thermal energy and as a result they increase in temperature. In our field study, we explore the viability of this system as a self-powered, off-grid, solar collector and find that it can provide enough hot water of approximately 80 degrees C for a household of four in areas where average daily solar irradiance is >4.5 kWh/m(2). We varied (1) the exposure angle, (2) PV panel type and (3) reservoir depth and found that in the limited ranges covered by our experiments the optimised configuration is with (1) an exposure angle of 14.7 degrees, (2) a bifacial mono-crystalline solar PV panel and (3) a reservoir depth of 12 mm (given a fixed inlet water flow rate). The theoretical model of the device that is built, tracks energy losses with time and outputs the average reservoir temperature at each five-minute time-step. We validated this model with the obtained data during the field study. Then, this model is used to perform a sensitivity analysis on the parameters in testing and beyond (such as primarily insulation types and thicknesses), to provide a direction for further development and improvement.