03 Mar 2021

Tunnel between Italy and Austria to provide sustainable geothermal heat

The drainage water from the Brenner Base Tunnel could supply Innsbruck city quarters with energy in the future, as being explored by researchers led Graz University of Technology.


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The drainage water from the Brenner Base Tunnel could supply Innsbruck city quarters with energy in the future, as being explored by researchers led Graz University of Technology.

After its completion in about ten years, the Brenner Base Tunnel is expected to relieve the traffic between Italy and Austria. The Brenner Basistunnel Gesellschaft (BBT SE) and the Innsbrucker Kommunalbetriebe want to generate a further benefit together with the Institute for Rock Mechanics and Tunneling of the Graz University of Technology and determine the geothermal potential of the tunnel, as institute director Thomas Marcher explains: “We are investigating whether and how the drainage water from the Brenner Base Tunnel can be used for climate-friendly heating and cooling of houses or even entire city districts in Innsbruck. ”

Trend-setting results within one year

Within a year, the researchers want to use simulation models for the Brenner Base Tunnel to make an initial estimate of the infrastructural measures that are needed to achieve the highest energy yield. Project coordinator Thomas Geisler from the Institute for Rock Mechanics and Tunneling gives examples: “We are testing possibilities of whether and how we can raise the temperature of the drainage water to a higher level. A conceivable variant are so-called absorber techniques (energy anchors or energy soles, note), which are installed on the inner wall of the tunnel and absorb the mountain heat. In addition, we want to clarify how a sensible economic distribution of the water can take place in the households and how the heat pumps and the heat exchangers have to be planned or adapted. ”


The results ultimately serve the BBT SE and the Innsbruck municipal operations as a basis for decision-making for further economic and technical implementation.

Tunnel inclination and third tube as cost advantages

In their planning, the researchers benefit from the unique selling points of the 64-kilometer-longest railway tunnel in the world: Due to its length and its incline towards Innsbruck, the tunnel water in the Brenner Base Tunnel automatically flows towards the city without additional pumping. In addition, there is an exploratory tunnel under the main tunnels, which is almost completed and through which the drainage water from the main tunnel will in future also be drained. In the exploratory tunnel, concepts for generating energy can thus be developed that do not hinder railway operations. The implementation is therefore associated with less effort and lower costs than was the case with comparable projects – in Stuttgart (Fasanenhof tunnel), Switzerland (Gotthard base tunnel) and in Jenbach (Unterinntaltrasse).

Research institutions work together on solutions

Nevertheless, the challenge remains great. In order to be able to identify the most efficient system, the researchers need to know the amount of water that will be available after completion of the Brenner Base Tunnel and its temperature. They are supported by teams from the AIT and the Federal Geological Institute as well as BOKU researchers from the Institute for Applied Geology and the Institute for Energy and Process Engineering. “We designed the project to be very interdisciplinary, especially since it requires expertise from the fields of hydrogeology, tunneling, process engineering and hydrochemistry for the best result,” says Geisler. The necessary data for the investigations come from Brenner Base Tunnel Society BBT SE and the Innsbruck municipal operations.

Pioneering work also for existing projects

Another important core aspect of the work aims at the transferability of the concept to other, also existing tunnels. In the course of the project, the research group will investigate which technologies can be used to supplement current tunnel construction projects and to retrofit already active tunnel systems in order to fully exploit their energetic potential. “The space available above ground is becoming increasingly scarce and the energy requirement increasing. Underground structures are natural sources of energy and heat. Not only from an ecological point of view, but also for reasons of space, it is only good and sensible to use this infrastructure more intensively for energy supply in the future, ”says Thomas Marcher hoping that it will serve as a role model for tunnel planners and operators around the world. With all the confidence that the heat will be used sustainably, the rock mechanic urges a prudent approach: “We have to intensively check how the heat extraction affects the thermophysical properties of the rock in the long term. Because what we all don’t want: a cooling of such a dimension that diminishes the energy generation in the long term. ”


At TU Graz, this research is anchored in the “ Fields of Expertise” Advanced Materials Science and Sustainable Systems, two of the university’s five strategic focus areas. The project is funded by the Federal Ministry for Climate Protection, Environment, Energy, Mobility, Innovation and Technology as part of the “ City of the Future ” program of the Austrian Research Association (FFG).

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