Deep geothermal energy research in the Alps

Simply converting the disused railway tunnel in the Saint-Gotthard Massif into an underground research facility delivered major insights into how deep geothermal energy can be accessed safely. And when the first experiments were conducted in the Bedretto Underground Lab, so many research groups from Switzerland and abroad showed interest that a veritable traffic jam developed. To increase capacity, a second underground lab has been under construction since 2022 – also with generous support from the Werner Siemens Foundation.

In principle, deep geothermal energy production is fairly simple: first, two holes are drilled deep into the earth’s crust where the rock is hot – at a depth of five kilometres, temperatures range between 150 and 200 degrees Celsius. Then, in a second step, water is pumped into the first borehole, where it begins seeping through fine cracks in the rock until it reaches the second borehole. On its way, the water gets so hot that it exits the hole in the form of steam. This steam is then channelled into a turbine and used to produce electricity. A major drawback, however, is that hard rock like granite is nearly impermeable by nature, which is why geologists provide some outside assistance: they apply extreme pressure to fracture the rock. This procedure requires painstaking care, as it can otherwise trigger earthquakes, as happened fifteen years ago in Basel.

In their current work, the researchers in the Bedretto Underground Lab are seeking the best way to generate fissures in the granite. A promising procedure has already been tested: a multi-step stimulation in which fissures are provoked section by section, staggered over time. This project, called “Destress”, was carried out in 2021. “It’s a major breakthrough for deep geothermal energy research,” says Marian Hertrich, geophysicist at ETH Zurich and manager of the Bedretto Underground Lab.

The researchers in the team led by project initiator Domenico Giardini are also testing an alternative method of energy storage in heat reservoirs. Rather than drilling down 5000 metres to produce electricity immediately, they want to determine whether a moderate depth of 1500 metres would be sufficient for heating the water during the summer months when electricity is available in great supply. During the cold winter months, power could then be generated from the heat stored in the reservoirs. Heat reservoirs have two major advantages over deep geothermal energy production. First, dangerous earthquakes are much less likely to be triggered at more moderate depths. Second, costs are lower – partly due to savings on infrastructure expenses, but also because the electric power needed to pump the water through the rock layers is practically free in summer.