Interdisciplinary Review of Medium-deep Aquifer Thermal Energy Storage in North Germany

High Temperature Aquifer Thermal Energy Storage (HT-ATES) has developed from a demonstration stage to a mature technology over the past decades. The specific storage capacity costs are lower by a factor of 20 compared to above-ground storage systems. Depending on geology, system configuration and temperature level, medium deep aquifers (approx. 400 m-1,000 m) enable seasonal heat storage from 1 GWh/a up to 100 GWh/a. Typical heat recovery factors are in between 60-80 %. However, only three systems have been built and reached normal operation in Europe. Moreover, although substantial parts of the subsurface in Germany, for example, are suitable for ATES systems, over 10 years have passed since the most recent project has been put into operation. Despite substantial advantages and a great potential of bridging the gap between constant production and seasonally varying demand, ATES is quite complex and conditional. Critical hydro-geological conditions (e.g. permeability, porosity, mineralisation) as well as relevant ordinances and regulations from the mining and local water authorities should be complied with. In addition, geothermal projects are not always supported by public acceptance as drilling boreholes today is a sensitive and emotional topic. This contribution deals with an interdisciplinary approach to evaluate all parameters (geology, legal classification, public acceptance, water chemistry, applications/revenue models and drilling technology) affecting a cost-effective operation of ATES systems in North Germany. One main objective is to identify possible locations for ATES in the North German Basin and to derive generalizable success factors. Preliminary results and an overview of the project supported by the Federal Ministry of Economic Affairs and Energy are presented. The project consortium consists of Leuphana University of Lüneburg and GeoDienste GmbH, supported by GeoEnergy Celle e.V