Experimental investigation of a distributed photovoltaic heating system based on building envelope thermal storage

Low-carbon heating in farmhouses can be achieved using photovoltaic (PV) heating. However, the severe mismatch between the PV energy supply and the building thermal load requires expensive energy storage devices and control systems. In this study, a controller-less PV heating system utilizing the building envelope for thermal storage was evaluated on a farmhouse in northern China. The building envelope simultaneously functions as the heating terminal and is composed of insulation boards, electric heating wires, and the thermal storage wall. PV electricity is fed to be absorbed by the electric heating wire to produce heat. The thermal storage wall absorbs the heat generated by the heating wire before releasing it into the room through convection and radiation. Long-term monitoring reveals that the black bulb temperature of the farmhouse was above 16 degrees C for more than 60 % of the time throughout the heating season. The building envelope acting as a thermal reserve improved system supply and demand matching by 77 % and the indoor temperature fluctuation was reduced by about 47 %. The thermal storage wall can provide 58 % of the heating energy when there is no PV power supply. The payback period of the heating system is only 6.5 years, verifying the good rate of return of the system. This study proposes a lower cost energy storage solution for PV heating than previous studies, and engages the building envelope into the building energy system.