The Geothermica consortium G2C (Galleries2Calories), which includes American and European partners, is investigating the use of mine water in local abandoned underground coal mine workings to cool a large computing facility south of Edinburgh. The heated water will then be stored in and transported several kilometers through interconnected mine workings where its heat can be extracted via heat pump technology for direct heating. This concept is known as a Geobattery. If successful, the project could provide a circular economy blueprint for utilizing legacy mines in the UK, the US, and worldwide as recycled thermal energy storage networks. Abandoned flooded coal and shale mine networks stretch throughout the central belt of Scotland, the Appalachian region of the US, and elsewhere. Most abandoned mines are flooded with water that has almost no seasonal variation in temperature, making them ideal heat sources for heat pumps. The interconnected mine workings minimize the need for drilling, typically the most expensive part of any geothermal energy project involving heat pumps. However, the storage of waste industrial heat in mine workings is challenging both technically and commercially, due to the complexity and uncertainty of the interconnected and often collapsed mine workings. Additionally, dynamic geomechanical, geochemical, and biological processes arise from operation of the Geobattery, as it imposes thermal and hydrological changes to the system. A sophisticated coupled-process modeling approach can be used to predict short- and long-term performance of the Geobattery, help in design selection, and evaluate risks. Modeling efforts began by developing models of the natural state of the system, and calibrating them against newly deployed monitoring data from the site in Scotland. Groups at LBNL and INL are using deterministic and stochastic methods, respectively, with the goal to assess the pros and cons of each approach before embarking on modeling the response of the system to Geobattery operation. An overarching goal of this research is to increase knowledge and decrease the risk for future mine-water geothermal energy storage and extraction projects.

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