Technical lessons learned from the usage of geothermal mine water for heat supply and economic scenarios to predict feasibility

The thermal utilisation of abandoned mines can be a valuable renewable energy resource for space heating. However, comparatively few mine water geothermal projects have been realised. In this work, key enablers for the economical success of mine water heating systems are investigated based on the analysis of a seven-year-old system in the city of Bad Ems, Germany. Testing various potential carbon price evolutions, this work aims to identify the necessary market conditions for the financial feasibility of the mine water heating system and to draw general conclusions for other sites. Bad Ems benefits from a comparatively high discharge temperature of 25 ∘ C , but the system is negatively affected by mineral precipitation and heat losses. Despite these drawbacks, the system substantially reduced operating costs and carbon emissions compared to the previously installed gas heating system. This study finds that financial savings are expected to increase significantly after the opening of the European Emissions Trading System in 2027. As a result, the analysis predicts an amortisation period of between 14 and 22 years, comparable to an air heat pump. An improved design could further decrease amortisation periods by four years. For a more ambitious amortisation period of ten to 15 years, this study suggests that an average carbon price between 85 and 265 EUR per ton would be necessary. Based on these results, public subsidies and low prices for electricity remain critical for the realisation of mine water heating systems in an improved economic environment. • Technical analysis of a mine water heating system reveals optimisation potential. • Heat loss in heating network and mineralisation at heat exchangers most critical. • System saves money and carbon emissions compared to previous gas heating. • Amortisation periods vary between 14 to 22 years depending on carbon and energy prices. • Subsidies needed to cover high investment costs in an improved economic environment.