Potential of source-side thermal energy storages in geothermal and solar thermal supplied heat pump systems

Until today the German building stock is still mainly supplied by fossil fuels to provide heating and domestic hot water. Supply solutions are needed to establish a high share of renewable energies in existing buildings and thus contribute to the overall transition of the heating sector. The combination of geothermal and solar thermal energy in electric driven heat pump systems have proven to be an efficient solution for existing buildings despite the higher supply temperatures on the demand side compared to new buildings. This work examines the potential of an additional source-side thermal energy storage on the economic and efficient operation of integrated heat pump systems supplied by solar and geothermal sources. The aim is to investigate whether this system configuration is suitable for achieving an increase in the system efficiency compared to an equal system that is not equipped with an additional source-side storage and to quantify the additional costs that are incurred for the application. The system is modeled in the simulation environment of Polysun, where parameter studies are conducted for different storage sizes and number of collectors under consideration of real measured data from an existing building with moderate level of refurbishment. The results in our recent simulation set up show that geothermal and solar thermal supplied heat pump systems are slightly benefitting only in a few cases from an application of an additional source-side storage regarding the overall system-efficiency. Further studies are necessary to optimize and investigate the control behavior of the system and to further quantify the potential of source-side thermal energy storages in geo- and solar thermal supplied heat pump systems.