The implementation of renewable energies and their increasing integration into the power supply of Germany is currently a primary task of the country’s energy policy. However, the problem of energy storage itself has not yet been solved. Besides new energy storage technologies like wind energy-based hydrogen production or new batteries or even conventional Pumped Hydro Storage (PHS) facilities, the Underground Pumped Hydro Storage (UPHS) concept represents another possibility for energy storage. Due to the coal mining history of the Ruhr area in Germany, the last mine in the Ruhr area, Prosper- Haniel, will stop its black coal mining in 2018. 200 years of mining activities will then become history in this region. In general, this mining infrastructure may feasibly be used for energy storage concepts. Thus, the mine Prosper-Haniel has been analyzed for becoming a follow-up facility as an underground pumpedhydro electrical storage project. The developed concept is based on newly introduced storage tunnels deep in the earth which can hold approximately 600,000 m3. The conditions make it a suitable location for storing large amounts of energy for short periods of time, which contributes to the balance of the regional energy grid. Despite the potential of this existing network of tunnels, the future post-mining underground water levels will compromise its use, and therefore alternative options to create a new storage structure have been proposed. There is also an enormous energy potential since the vertical hydraulic head could be up to 600m inside the existing shafts and their surrounding infrastructure. This head is sufficient to operate the pumped hydro storage with small to medium volumes of water. Facilities of this type have not yet been developed or realized, therefore an assessment of feasibility and economic viability needs to be carried out. The new storage ring structure (underground reservoir), which consists of drilling 15.5 km of new tunnels, takes advantage of existing shaft infrastructure. It offers about 835 MWh for each production cycle (4h) in the system with a total power capacity of 200 MW. The ongoing research describes the most relevant aspects for developing the project, considering construction, geotechnical, geological, and energy market restrictions. For the evaluation of feasibility and the identification of requirements, an interdisciplinary research group has been formed. This group consists of expert researchers from the areas of hydraulic engineering, geology, geotechnical engineering, energy economics and social science. Such a group works in close cooperation with the coal mine owner RAG AG. Besides the RAG AG, there are further departments of the University of Duisburg-Essen, departments of the Ruhr-University of Bochum, the mining consultancy DMT GmbH and the social research institute RISP involved. The main results concern the technical and economic feasibility of using the existing mine infrastructure for the potential development of an underground pumped-hydro storage facility. The assessment of the Prosper-Haniel mine is a pilot study which could be used for future assessments of intended underground pumped-storage facilities in post mining situations. For further information please visit: www.upsw.de