UnlockTES – Unlocking High-Temperature BTES potential under Swiss groundwater constraints

Seasonal thermal energy storage is essential for decarbonising Switzerland's heating sector, which still accounts for around a third of national emissions. Borehole Thermal Energy Storage (BTES) is a particularly promising option thanks to its modularity, low surface impact, long lifetime and moderate cost. Operating these stores at high temperatures (up to 60–70 °C) increases their energy density. However, higher temperatures also increase the thermal impact on the surrounding ground and groundwater, and Swiss water-protection rules (notably the "3 K rule”) currently make such systems difficult and costly to permit. A further obstacle is that energy-system design and subsurface behaviour are usually assessed separately, even though they are closely linked.