St Gallen weighs a cautious return to deep geothermal energy

Thirteen years after an earthquake stopped St Gallen’s geothermal experiment, the canton is preparing to look underground again. A new assessment has identified parts of eastern Switzerland as suitable for renewed exploration of deep geothermal energy, a technology that could supply locally produced heat while Switzerland seeks to expand renewable sources.

The canton commissioned a specialist consultancy to examine medium-depth and deep geothermal potential. Its 178-page final report describes the region as “geothermally attractive”. Among the locations mentioned are Buchs, Ebnat-Kappel and Widnau/Diepoldsau.

The timing reflects a wider shift in Swiss energy policy. The climate crisis and concerns about energy security have increased pressure to develop domestic renewable resources. Geothermal energy can provide heat throughout the year, unlike sources that depend on sunlight or wind conditions. The technology also carries a difficult local memory. St Gallen city’s earlier project ended after an earthquake, leaving behind a 4,400-metre borehole and deep public scepticism about drilling beneath settled areas.

The government’s new study does not announce a construction project. It lays out geological prospects and recommends testing them gradually before the canton commits to expensive deep wells.

More than 200 gigawatt-hours of annual heat could come from four promising sites. The study says that output would cover about one-fifth of the target in St Gallen’s cantonal energy strategy for renewable energy production. The estimate gives geothermal energy a measurable place in the canton’s transition plans, even though no site has yet been approved for drilling.

The geology offers several reasons for the optimism. Glacial channels formed during the last ice ages, including those around the Rhine Valley, reach approximately 300 to 600 metres below the surface and contain unconsolidated rock. The report also points to extensive fault and fracture zones that may be permeable and contain groundwater. Such structures can offer pathways for heated water and improve the chances of extracting usable energy.

The most favourable locations are those where drilling can intersect these underground zones. Buchs, Ebnat-Kappel and Widnau/Diepoldsau are among the places named in the assessment, though the available source does not identify a final shortlist or confirm that any one municipality will host a well.

The figures describe potential, not guaranteed production. Actual yields would depend on drilling results, water flows, temperatures and the ability to manage underground pressure safely.

The canton’s proposed first move is to drill less deeply and learn more. The report recommends testing a “shallow play” before attempting the most ambitious wells. In geothermal development, a play is an area believed to contain exploitable underground resources. The staged approach reflects two constraints identified by the study: drilling costs rise sharply with depth, and geological knowledge becomes less certain farther below the surface.

St Gallen has many boreholes, but most are geothermal probes reaching only 200 to 300 metres. They provide useful information about near-surface conditions, yet they do not map the deep formations that would determine whether a large geothermal system can operate. The former city project remains the major exception, reaching 4,400 metres before the earthquake ended the effort.

A shallow investigation could allow researchers and engineers to collect more local data, refine geological models and identify promising structures before the canton or private investors spend heavily on deep drilling. It could also give municipalities more information to discuss with residents.

The report’s sequencing matters because a new project would have to demonstrate more than geological promise. It would need a credible drilling plan, monitoring systems and clear thresholds for stopping work if underground activity became unsafe.

Any revival will have to confront the earthquake that ended St Gallen’s first attempt. The earlier project made the risks of deep geothermal drilling tangible for residents and policymakers. When the effort was halted, the canton lost momentum, and no major deep geothermal project followed in eastern Switzerland.

The pause extended beyond St Gallen. A legal framework was still being developed in Thurgau, while Geo-Energie Suisse’s project in Etzwilen remained on hold for years. The company is now advancing a geothermal project in Haute-Sorne, in the canton of Jura. Those developments provide a wider Swiss context for St Gallen’s deliberations, but they do not remove the need for local scrutiny.

Public confidence will depend on how the canton handles uncertainty. The new study identifies promising geological conditions, yet it does not guarantee that deep drilling will be commercially viable or free of seismic effects. Residents will also want clarity on who bears the cost of failed wells, how monitoring data will be published and which authorities can intervene.

For now, St Gallen has a technical roadmap rather than a final investment decision. The next stage is likely to involve more subsurface investigation, local consultation and a closer test of whether renewable heat can be developed without repeating the consequences of the earlier project.