Keywords :
Seasonal Storage, Renewable Energy Integration, Massive Energy Storage, Heat Pump, Organic Rankine Cycle
Abstract :
[en] Many countries are progressing towards energy systems largely based on renewable resources. To enable this
transition, it is essential to develop new solutions for reliable and flexible energy storage and distribution.
Flooded abandoned mines offer high potential to host local energy communities, more than 9000 such sites
exist in Europe alone, given the opportunity to act as large-scale thermal storage systems and providing services
that support grid stability. Within the framework of the European WeForming project, this study investigates the
economic analysis of a flooded mine in southern Belgium as a multi-service demonstrator for heating and
electricity dispatch. The mine infrastructure enables daily, weekly and seasonal thermal storage using several
flooded caverns: 6000 m³ at 45–55 °C, 10000 m³ at 25–40 °C, and 120000 m³ at 15–25 °C. In addition, a 350000
m³ volume at 8–10 °C serves as a cold sink. A yearly simulation model developed in Python is presented
alongside the construction progress of the demonstrator, which is expected to be fully operational by mid-2026.
On the demand side, the system is designed to provide services to the electricity grid, participate in the day-
ahead market, supply process heat at 120 °C to an industrial consumer, and deliver low-temperature heat to a
district heating network (DHN). The results demonstrate the strong techno-economic potential of the concept,
with a Levelized Cost of Energy (LCOE) of 310.85 €/MWh for the whole system, decreasing significantly when
only the CB subsystem is considered (209.21 €/MWh), and even further when grid taxes are excluded, reaching
values around 108.72 €/MWh. The discounted payback period is about 23.8 years for the entire system but falls
to 6.21 and 3.51 years for the CB, depending on the inclusion of taxes. These results are based on real
performance and cost data, underlining the relevance of flooded mines as multi-service assets and motivating
further research and deployment.
