Joint press release by Green Therma and GFZ Helmholtz Centre for Geosiences

Danish geothermal technology company Green Therma has successfully commissioned its new technology – a coaxial closed-loop system with vacuum insulation – for the first time anywhere in the world under real geothermal conditions at the research site of the GFZ Helmholtz Centre for Geosciences in Groß Schönebeck, north of Berlin.

The demonstration marks an important step from installation to operation. Making use of one single existing borehole, water is now circulating through the closed-loop system, vacuum integrity of Green Therma's DualVac™ insulation technology has been established, and geothermal heat is being brought from more than three kilometres underground to the surface at temperatures suitable for direct use. 

Deep geothermal heat has extensive potential as a stable, local source of renewable energy, but its deployment has traditionally been limited by the availability of suitable underground hot-water reservoirs.

Green Therma’s Heat4Ever™ system takes closed-loop geothermal technology one step further by delivering more heat to the surface at higher temperatures. This could significantly expand where geothermal heat can be produced – bringing it closer to cities and industrial sites without relying on underground hot-water reservoirs.

“The heat is already there, right beneath our feet. We need to get better at using this enormous natural resource and bringing it to where people and industries need it. What we have demonstrated at Groß Schönebeck shows that we can access deep geothermal heat and bring it to the surface at temperatures that can be used directly without heat pumps. We are turning the heat beneath our feet into a new source of baseload heat – available around the clock and with very little electricity use,” says Jørgen Peter Rasmussen, Founder and CEO of Green Therma.

Proven under real geothermal conditions

At the core of Heat4Ever™ is Green Therma's DualVac™ vacuum-insulated completion, designed to minimize temperature loss as heat travels from deep underground to the surface without the need to extract or reinject formation water: Cold water is being injected into the outer section of the coaxial tube and heats up on its way down before flowing back upwards through the inner section of the pipe. Thanks to the vacuum-isolation between inner and outer section, there is nearly no loss of the temperature gain on the way back up. As for the Groß Schönebeck test site, the rock temperature at a depth of more than 3,000 m is approximately 130 °C. Depending on the flow rate, the water injected into the pipe heats up to around 70–80 degrees during operation, which is the temperature it maintains at the wellhead for further use.

With the system now operating, continued testing at Groß Schönebeck will generate further data on long-term performance, stability, and heat-extraction potential under different operating conditions.

Science and industry working together

The project is being carried out in close collaboration with GFZ at its Groß Schönebeck geothermal research site north of Berlin. The research environment provides the infrastructure and scientific expertise to demonstrate new geothermal technologies under real subsurface conditions. 

“Groß Schönebeck provides a unique opportunity to investigate this technology under real-world subsurface and operating conditions. The successful installation and start of circulation mark an important milestone. The operational test will now generate valuable scientific data on long-term performance and help us evaluate the potential and integrity of closed-loop geothermal systems,” sais Prof. Dr Hannes Hofmann, Leader of the Helmholtz Young Investigator Group Advanced Reservoir Engineering at the GFZ Helmholtz Centre for Geosciences.

“Robust data from full-scale operations are essential to advancing geothermal technology. Groß Schönebeck helps bridge the gap between research and application, generating the insights needed to improve models and advance the next generation of closed-loop geothermal systems,” says Prof. Dr Ingo Sass, Head of the Geoenergy Section at the GFZ Helmholtz Centre for Geosciences.

From demonstration to full-scale heat production

Green Therma is already taking the technology to full scale with a project developed in partnership with Aalborg Forsyning in Denmark. The project will bring Heat4Ever™ from demonstration to commercial-scale operation, delivering geothermal heat directly into the local district heating network under a 30-year heat offtake agreement. Preparation is underway, and drilling will begin in early 2027.

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About Green Therma

Green Therma is a Danish geothermal technology company founded in 2023, developing Heat4Ever™, a deep closed-loop geothermal solution for district heating and industrial heat. Green Therma combines geothermal development with decades of experience in drilling, well design and completion from the energy industry. Headquartered in Denmark, the company has a presence in Germany, Norway and the United States.

Green Therma has just been nominated by the German-Danish Chamber of Commerce for the ‘German-Danish Newcomer of the Year 2026’ award. This prize recognises young and innovative companies that contribute to business relations between Denmark and Germany.

www.greentherma.com

Learn more about the Heat4Ever™ pilot project: www.greentherma.com/gfz

Media Contact:

Green Therma

Pernille Fredgaard Schiander
Head of Marketing & Communications
+45 2564 6141

GFZ Helmholtz Centre for Geosciences 

Dr. Uta Deffke
Deputy Press Officer | Communication and Media
+49 331 6264 1049
presse@gfz.de