Janne Hirvonen

High Latitude Solar Heating Using Photovoltaic Panels, Air-Source Heat Pumps and Borehole Thermal Energy Storage

A solar community of 100 passive houses was designed for high latitude Finnish conditions. Typical solar thermal energy generation was replaced by solar electric system which was used to operate heat pumps. Short-term waterbased thermal storage tanks were charged with an air-to-water heat pump and then discharged to a seasonal thermal storage system in the form of borehole thermal energy storage (BTES). With total PV capacities of 240 to 600 kW, 78 to 97% of space heating and domestic hot water was provided by renewable energy from the local heating grid. Utilizing a water-to-water heat pump between low and high temperature water tanks increased the efficiency of the air-source heat pump. Varying the flow rate of borehole storage provided very minimal benefit.