Performance assessment of subsurface seasonal thermal energy storage coupled with a geothermal-powered district heating network: an example from the German Molasse Basin

High-Temperature Aquifer Thermal Energy Storage (HT-ATES) can provide flexibility to the heat provision systems as required by the transient fluctuation in the thermal energy demand. Such multicomponent-system concepts are currently experiencing increasing attention in the German Molasse Basin (southern Germany), where, HT-ATES can compose an essential element of the energy systems, contributing towards the transition to decarbonized heat supply. In this work, we highlight an example from the greater area of Munich to analyze the efficient integration of seasonal high-temperature heat storage in the highly utilized Lower Cretaceous and Upper Jurassic geothermal reservoir (North Alpine Foreland Basin) into a local District Heating Network (DHN). The favorable geographic location in the greater area of Munich holds the advantage of large amounts of available excess energy and suitable subsurface conditions for HT-ATES concept development, combined with large DHNs to utilize the surplus energy. The case study network operates within a range of 72 °C up to 94 °C in dependency to the atmospheric temperature. It is equipped with a geothermal plant comprising its prime heat source element, while it is further supported by a supplementary conventional fossil-fuel powered heat provision unit to cover peaks in demand and redundancies.

Our energy system analysis aims at extending the investigated network by numerically integrating the HT-ATES in the form of a seasonal heat provision component to cover peak loads, and thus partly replace the fossil-fueled heat generator. To this end, we initially elaborate on the efficient design and operation of the multicomponent energy system with focus on the integration of the HT-ATES into the heat supply scheme. Subsequently, the co-simulation approach that captures the interaction between the different subsystem elements is in focus. The HT-ATES system is simulated with the MOOSE-based GOLEM numerical code, and describes the thermal-hydraulic processes triggered by the storage of high-temperature fluids with 110 °C into the Lower Cretaceous and Upper Jurassic geothermal reservoir. In parallel, the DHN is modelled with the TRNSYS-TUD software environment and, apart from the thermal-hydraulic parameters of the analyzed DHN, it additionally provides the transient accumulated load curve. The coupling of the two systems requires the exchange of both the operating mass fluxes and fluid temperature between the two modelled systems.