Techno-economic parametric study of a low-temperature district heating network coupled with underground mine thermal energy storage

This study presents a techno-economic analysis of a low-temperature district heating system coupled with underground mine thermal energy storage (UTES) in Martelange, Belgium. The system integrates photovoltaic panels, a geothermal heat pump, and a large water-filled mine reservoir to store seasonal thermal energy. Dynamic simulations in Modelica evaluate the impact of storage volume, storage cost, PV capacity, and battery size on key performance indicators such as COP, seasonal COP, self-consumption, self-sufficiency, storage efficiency, and cost of energy (COE). Results show that larger storage volumes increase renewable energy self-consumption but reduce seasonal performance due to higher thermal losses. Economically, storage investment cost dominates COE, while increasing PV or battery capacity improves self-sufficiency but does not always reduce costs. The analysis highlights a trade-off between flexibility, energy autonomy, and cost, demonstrating that intermediate storage sizes with moderate investment achieve the optimal balance for efficient and economically viable renewable heating systems.