Thermal energy storage for increasing self-consumption of grid connected photovoltaic systems: A case for Skjetlein High School, Norway

Abstract

Grid-connected photovoltaic systems installed in buildings have the option of exporting excess energy when the electricity generated is greater than the building’s energy demand. However, with no incentives and when purchasing electricity is higher than selling electricity, mechanisms for increasing self-consumption of the excess solar energy become important. The potential of thermal energy storage (TES) for increasing self-consumption in the cases of electrical photovoltaic installations has been investigated in this work. A model has been developed for the PV integrated with TES system and demonstrated with a case study. The TES was intended to enable the PV system to contribute to the supply of space heating.

Electricity consumption, PV generation and PV export, and space heat demand data for two years were used for the analysis. The existing system without TES and a system that includes TES were modeled using the TRNSYS program. A combination of the TRNSYS and the optimization program GenOpt was employed to determine the optimum size of the TES. The result of the case study with an installed PV capacity of 235 kWp showed that TES with a tank volume of 10 m³ and a thermostat temperature setpoint of 90 °C would be appropriate for the system. This resulted in an annual average increase of 26 % in self-consumption of the electrical PV production in the buildings compared to the existing case with no energy storage system. Thus, the annual heat demand delivered to the buildings by a boiler decreased by 5 %.