Potential for Seasonal Electricity Storage in Borehole Thermal Energy Stores with Heat Pumps

Abstract: In Sweden, there is a substantial increase in renewable power generation that affects the elec-tricity market. At the residential, PV diffusion spreads in the last years due to price drop, while use of heat pump is consolidated. This thesis aims to evaluate the technological potential and economic value of seasonal storage of electricity in a thermal medium using boreholes and heat pump for a multi-family house in Sweden in a context of high renewable market. An existing GSHP-PV system model is implemented in TRNSYS with the addition of an in-line heater on the boreholes circuit. Its function is to heat the borehole field during PV peaks or low electricity price. The performance of the system is evaluated in terms of renewable and consumption impact with Self-Consumption, Solar Fraction and Seasonal Performance Factor, while Total Life Cycle Cost defines the economic feasibility of the system. In order to estimate several price scenario, an electricity market model is developed and applied to forecast the hourly electricity price in future in Sweden with high wind and solar penetra-tion. The results suggest that the configuration studied does not benefit from seasonal storage of elec-tricity. Since the increase of electric demand due to the borehole heater, self-consumption is generally improved despite solar fraction depends greatly from the only use of PV over produc-tion or grid prices. Seasonal peak shift and SPF improvement are not demonstrated, although there is an increase of TLCC. This leaves the system without storage the most profitable, despite the use of electric boilers or heat pumps at the borehole heater.