German national project High temperature mine thermal energy storage pilot plant
The aim of the German HEATSTORE sub-project is to create a technically and fully functional high temperature mine thermal energy storage (HT-MTES) pilot plant (see fig. 1) for the energetic reuse of an abandoned coal mine, with the emphasis on an extended operating and monitoring phase during the project lifetime of three years. The generated data can be exploited for the implementation and dissemination of future deep geothermal storage systems. The conceptual idea is based on the storage of seasonal unutilized surplus heat during the summer from solar thermal collectors within the mine layout and to use the stored heat during the winter for heating purposes of the institute buildings of the “Fraunhofer Institut für Energieinfrastruktur und Geothermie” (IEG).
Mine thermal energy storage
The concept of this pilot plant aims at the reutilization of an abandoned coal mine, which is directly located under the premises of the IEG in Bochum, as a high temperature mine thermal energy storage. This area also includes the drilling and test facility site of the IEG, on which the Bo.REX (Bochum Research and Exploration Drilling Rig) is currently located. This leads the way of a very cost effective exploration of the flooded colliery in a depth of approx. 75 m below ground. The injection and production well with the IEG drilling rig. Currently, the groundwater level resides at a depth of approximately 21 m below ground. Overall, the colliery produced 37,043 tons of coal. Based on a calculation with a coal density of 1.35 g/cm3, we can assume a void volume of approx. 27,439 m3. This volume does not include any drifts and shafts, which need to be analyzed based on the mine layout. Considering the effect of mine subsidence, the remaining void volume will most likely be in the range of approx. 10%. Utilizing a Δt of 50 K within the mine water, a heat capacity of approx. 165 MWh, which resembles the yearly heat demand of the IEG compound, could be stored within dedicated drifts and former mining areas of the colliery for the heating season. Based on this first evaluation, the yearly IEG heat demand could be substituted by emission free solar thermal energy. After the two year pilot phase is concluded, the integration of the MTES into the district heating network of the “unique Wärme GmbH” could be tackled, as two CHP plants (9 MWth) were put in operation in July 2018 in a very close proximity of approx. 350 m to the IEG pilot plant.
Overall, the realization of the mine thermal energy storage can be allocated with a TRL of 8 and a CRI of 2, which is based on the following key facts:
- Cost effective drilling (IEG owned drilling rig and equipment).
- Colliery located below IEG premises.
- Heat source: Concentrated Solar Thermal plant and Combined Heat & Power plants in close vicinity for future integration
- Heat sink: IEG buildings
During the upcoming project phase, the implementation of three exploration wells into the existing mine layout of the colliery is foreseen. An approval by the water authority of Bochum for these three wells has been received. Pump and tracer tests will determine possible storage capacities.