For Vienna to become climate-neutral and independent of fossil energy in the future, it needs sustainable energy sources. Deep geothermal energy plays a special role here. After all, using geothermal energy from great depths is an emission-free, clean and safe alternative for heating buildings. And thanks to a huge deposit of thermal water at a depth of several kilometers, the German capital has good prerequisites for this.
“By using deep geothermal energy for heating, we are consistently pursuing our Vienna Climate Roadmap and making our city CO2-neutral by 2040,” affirms City Councilor Peter Hanke at a press conference. “Thanks to the thermal water deposit directly under the city and the well-developed district heating network, we are also in a unique starting position in a European comparison to be able to supply households with climate-neutral heat,” said City Councilor Peter Hanke.
Treasure in the deep
This “treasure in the deep” is to be exploited in the future through the construction of the first deep geothermal plant for Vienna. Wien Energie is implementing this lighthouse project and expects an investment volume of around 80 million euros. The Ministry of Climate Protection is funding the project with around 8 million euros. The start of preliminary work for the construction of the plant is planned for 2023. In the future, the deep geothermal plant will generate climate-neutral district heating with up to 20 megawatts, but the exact thermal output can only be finally determined after successful exploratory drilling. To make the plant even more efficient, Wien Energie is also planning to combine it with a heat pump.
After thorough preparation and examination of all factors, it was decided to start implementing this project. An area on the edge of the Urban Lakeside Aspern was identified as the optimal location for the new plant, which Wien Energie is currently acquiring from Wien 3420 Aspern Development AG to subsequently obtain the necessary permits for the drilling and construction work. Provided that all related procedures proceed according to plan, preliminary drilling work can begin in 2023. Drilling operations will take place in 2024, and the deep geothermal plant is scheduled to be commissioned in 2026. This pilot plant is the first major milestone for the rapid further expansion of deep geothermal energy in Vienna. By 2030, Wien Energie plans to develop a total of up to four deep geothermal plants in Donaustadt and Simmering with a total capacity of up to 120 megawatts. The expansion of deep geothermal energy is to continue after 2030 so that district heating will be generated entirely from climate-neutral sources by 2040.
“We are giving the green light for the heat turnaround! The goal is to get out of gas – and tapping deep geothermal energy is an important step in this direction. With our first deep geothermal plant for Vienna, we want to be able to supply up to 20,000 households with green heat from the depths as early as 2026,” says Michael Strebl, CEO of Wien Energie.
Several boreholes at a depth of over 3,000 meters are required to tap the thermal water. Due to this depth, which is about a hundred times deeper than the deepest subway station in Vienna, and since the boreholes only have a diameter of about 30 cm, no effects such as vibrations at the earth’s surface are to be expected. Nevertheless, drilling at such depths is technically demanding.
An exploratory borehole is used to investigate the nature and availability of the thermal water at the chosen location. After the successful exploratory well, two further wells are drilled. A system called “hydrothermal doublet” will be used for the planned exploitation. To this end, drilling will first be carried out vertically at a depth of around one kilometer, after which the boreholes will run diagonally in opposite directions to a depth of around 3,000 to 3,500 meters. The thermal water is pumped to the surface via one of the boreholes. After heat extraction at the surface via heat exchangers, the thermal water is returned to the same thermal water reservoir via the second borehole, thus creating a closed renewable cycle. The extraction point and the return point of the thermal water are about 4 kilometers apart. The heat generated in the deep geothermal plant is then fed into the district heating network.
The use of deep geothermal energy in Vienna is only possible because the “Aderklaa Conglomerate”, a water-bearing rock layer, is located beneath the federal capital. As an important basis for the development of this deposit, Wien Energie, together with partners from science, research and industry, has carried out a comprehensive investigation of the geological conditions under the city in recent years in the research project “GeoTief Wien”.
The scientific results are based on an extensive seismic 3D exploration of the “Aderklaa Conglomerate”. However, the research team was also able to use Wien Energie’s deep drilling in Essling, which has been in place since 2012, for a successful production test in the Aderklaa Conglomerate. Now that the technical means for exploring and exploiting geothermal deposits have developed accordingly in recent years, the Wien Energie project team is confident that the new wells will be successful based on the knowledge gained in the meantime. As with the “GeoTief Wien” research project, Wien Energie is working together with OMV, which will be responsible for the geological planning of the boreholes based on its decades of experience and technical expertise.
CO2 savings and potential for Vienna
The thermal water deposit under the city is so large that up to 125,000 Viennese households could be supplied with district heating from deep geothermal energy by 2030. This corresponds to an annual CO2 saving of 325,000 tons. To achieve this goal, the construction of further deep geothermal plants in the city area is planned, which in total could cover up to 20 percent of the total district heating generation.
One of the advantages of deep geothermal energy is that it is a CO2-neutral energy source that is available locally and around the clock and is accordingly independent of (fossil) energy imports. Deep geothermal energy is a reliable and, by human standards, virtually inexhaustible resource that provides heat and electricity on a long-term basis and at stable prices. In addition, unlike other alternative energies, deep geothermal energy has a small land footprint and is correspondingly gentle on the landscape. The plant itself is completely emission-free in operation.
Geothermal energy uses the heat stored in the earth’s crust. This comes from the earth’s core, which is between 5,000 and 7,000 degrees hot, and from natural decay processes in the earth’s mantle. The heat stored in the earth and the constant exchange of heat with the earth’s crust are inexhaustible by human standards. For every 100 meters of depth, the temperature in Central Europe increases by about three degrees. While near-surface use of geothermal energy involves shallow depths of up to 300 meters, deep geothermal energy requires drilling at depths of several thousand meters to tap thermal water deposits. Due to its millions of years of isolation in the rock, the thermal water stored in the eastern region of Vienna has a high degree of mineralization (e.g. salt content) and is therefore not potable. The water is extracted utilizing boreholes which, after the heat has been extracted from the surface, return the thermal water to the original thermal water reservoir. This creates a closed regenerative cycle.