Deep geothermal energy: Harnessing Vienna's subterranean treasure

In ancient times, the Etruscans and Romans harnessed the earth’s warmth for bathing and, later, to heat their floors. Today, this same heat source provides the volcanic island of Iceland with clean, sustainable power. Buried beneath layers of ancient rock, this vast but underutilized resource is known as geothermal energy, and it is now set to play a pivotal role in our journey to a climate-neutral future.

Geothermal energy makes use of the earth’s subterranean heat, sourcing it either directly from the hot rock or from heated underground reservoirs. In Iceland, this heat is just beneath the surface, where it’s easy to access. Elsewhere, deposits are found at great depths, presenting a more complex challenge. 

This is the case in the Vienna Basin, where thermal waters reside in the Aderklaa Conglomerate, a rock layer that dates back 20 million years. Located over 3,000 meters below the surface, the reservoir is over one hundred times deeper than Vienna's deepest subway station.

"This vast thermal reservoir spans several hundred square kilometers and reaches temperatures of over 100 degrees Celsius in places. It has the potential to deliver CO2-neutral heat to large parts of Vienna,” explains Bernhard Novotny, who leads geothermal energy projects at OMV.

‘deeep’ unlocks the potential of Vienna's underground heat

The reservoir was identified thanks to 'GeoTief Wien', a research initiative led by Wien Energie with support from OMV. Between 2016 and 2022, the project team collected comprehensive data on the geothermal capacity of this natural heat source.

The study made it clear that it would require significant infrastructure and expertise to extract the energy from so far underground. To meet the challenge, OMV and Wien Energie have teamed up to form ‘deeep,’ a joint venture that leverages the strengths of both companies.
 

“We bring over 80 years of experience, as well as our expertise in the fields of geology, geophysics, and deep drilling,” explains Bernhard Novotny. Wien Energie operates one of the largest district heating networks in Europe and already supplies around 440,000 private and 7,800 commercial customers with district heating. “We want to be CO2-neutral by 2040, and geothermal energy will play an important role in this,” says Peter Keglovic, project manager for deep geothermal energy at Wien Energie.

Deep geothermal energy explained

Deep drilling brings its technological challenges, but the fundamental process of harnessing geothermal energy is quite straightforward: “Wells are drilled deep into the earth’s surface to reach the reservoir. The hot water is then pumped up to a geothermal plant at the surface. From the plant, the heat is transferred directly to the district heating network. Once the water cools, it's cycled back into the underground reservoir, where it's naturally reheated by the Earth's geothermal energy," explains Bernhard Novotny.

Great potential at great depths 

Set to be constructed in Aspern, northeast Vienna, the Hydros Seestadt geothermal plant will be the 'deeep' joint venture's inaugural project. The plant will generate up to 20 megawatts of heat annually in combination with heat pumps starting from 2027.
 
This capacity will be enough to supply around 20,000 households. The long-term strategy is to establish multiple plants capable of producing up to 200 megawatts in total – enough to supply climate-neutral heat to 200,000 homes. "Vienna wants to be climate-neutral by 2040 and geothermal energy will play a major role in achieving this goal," says Peter Keglovic.

Balancing the benefits and challenges of geothermal energy

Geothermal energy boasts numerous advantages: it's a carbon-neutral and renewable energy source that operates in a continuous cycle, offering a consistent, local supply that reduces reliance on imports.

However, the localized nature of geothermal energy also comes with a drawback, as the heat cannot be transported over large distances. "Still, we are able transport it several kilometers using geothermal ‘highways’," explains Bernhard Novotny.

The positives of geothermal energy far outweigh its limitations according to Novotny: "It’s an extremely valuable resource, and key to helping us transition to climate neutrality, as well as increasing our energy independence." 

The discovery of thermal water in the Aderklaa Conglomerate, beneath a city with over a million inhabitants and already equipped with a well-developed district heating network, is extraordinarily fortunate. It's a subterranean asset that is just waiting for the proper expertise and infrastructure to unlock its full potential.

Watch the whole discussion in our OMV podcast "Rethinking Resources":