The High Temperature-Mine Thermal Energy Storage (HT-MTES) Project in Bochum, Germany

ABSTRACT The aim of the German HEATSTORE sub-project has been the development of a mine thermal energy storage (MTES) pilot plant for the energetic reuse of an abandoned small colliery below the premises of the Fraunhofer IEG in Bochum, Germany. In the summer 2020 three wells have been drilled into existing open mine voids from the IEG drilling site. During the winter of 2020/2021, a first MTES test operation has been carried out. The underground temperature has been recorded before, throughout and after a test operation by Distributed Temperature Sensing (DTS) as well as groundwater temperature and pressure loggers, which had been installed into the MTES wells. In spring 2021, a local district heat network (DHN) has been built up at the case study site. In summer 2021, a Concentrated Solar Power plant (CSP) as the future renewable heat source has been successfully erected at the demo site and was connected to the MTES via a common heat exchanger. INTRODUCTION The fundamental transformation of energy supply systems in Germany by 2050 represents an immense technological and economic challenge. The German government is focusing on the increased use of renewable energies and also the efficient use of energy. Based on this strategy, thermal energy storage systems represent an important foundation for the increased use of renewable energies. The transition to a sustainable energy supply requires the provision of large electrical as well as thermal storage capacities. The potential of volatile renewable energy sources can only be fully exploited through flexible management of the electricity and heat supply networks and a wide range of different storage technologies. The aim of this research project was to establish a pilot plant for seasonal heat storage within the former and no longer accessible IEG small colliery, which is located under the drilling site of the Fraunhofer Institute for Energy Infrastructures and Geothermal Energy (IEG) in Bochum, Germany. For this purpose, a numerical model of the former IEG small colliery was created within the HEATSTORE project and calibrated and validated by drilling three wells (MP1, MO1 and MI1) inside the mine workings of the IEG small colliery down to a depth of 64 meters. Within the scope of the project the wells were coupled with an above-ground solar thermal system.