MD-BTES construction and integration into a district heating grid: Insights and targets of SKEWS and PUSH-IT projects

Heat storage in crystalline basement rocks is a promising technology because it can provide a reliable source of heat and help to increase the efficiency of energy systems, and reduce greenhouse gas emissions. BTES systems work by circulating water in multiple borehole heat exchangers (BHE). However, BTES systems can be expensive to install, as they are sub-surface installations which require the drilling of medium-deep boreholes into often complex, sometimes fractured, heterogeneous lithologies.  Therefore, the geological uncertainties must be integrated from the early planning stage on.

This contribution focuses on the insights gained in the SKEWS (Seasonal Crystalline Borehole Thermal Energy Storage) project (research project SKEWS, project administrator Jülich, funding code 03EE4030A) and how these will be developed and rolled out in the Horizon Europe PUSH-IT project into follow-up sites at the European scale. The SKEWS project implements the world’s first demo site for Medium-Deep Borehole thermal energy storage in crystalline rocks, with three 750 m deep boreholes separated from an 8.6 m distance, drilled at campus Lichtwiese from the Technical University of Darmstadt, Germany.

From the drilling campaign carried out in the summer and autumn 2022, new insights have been gained into the implementation of BTES in such an urban environment. These insights go from the drilling technologies and verticality to the installation of the BHE. This knowledge and know-how will then be developed during the test phase and with the integration and surface connection of the BHE field with a section of the district heating grid.

Borehole heat exchanger installation, with insights on the experience gained on the optimal design, drilling, and completion, will be detailed. The planning and first results of the reservoir test phase and monitoring through optic fibre will be presented, as well as perspectives on targeted digital twin geological static and dynamic modelling of the reservoir and the district heating grid in a co-simulation workflow.

Such outputs will allow quantitative estimation of the technical and economic potential of the MD-BTES systems in existing or future district heating grids.