Nestled in the foothills of the Bavarian Alps, the town of Geretsried in southern Germany has become a focal point in the global shift toward renewable energy. While the world’s attention often turns to wind turbines and solar panels, a quieter but no less powerful force is at work deep beneath the surface, geothermal energy. In Geretsried, what was once an abandoned gas exploration site is now the centre of a pioneering geothermal project that could set a precedent for clean energy innovation across Europe and beyond.
A town with underground potential
Geretsried is not a large town, but it sits above one of the most promising geothermal reservoirs in Central Europe. In the 1980s, this region was originally surveyed by the oil and gas industry, which drilled several deep wells in the hope of finding commercially viable hydrocarbon reserves. While that effort yielded little success, it left behind an unexpected legacy, a wealth of subsurface data that geothermal engineers could later use to assess the heat and water resources available for energy generation.
The geological formation beneath Geretsried belongs to a sedimentary region stretching across much of southern Germany and into Austria and Switzerland. This basin is particularly well-suited to deep geothermal projects as it contains porous and permeable rock layers that allow hot water to circulate at depths of more than 4000 metres, where temperatures can exceed 140°C.
The evolution of the Geretsried Project
The Geretsried geothermal project, now being developed by Eavor Technologies, represents a cutting-edge approach to harnessing geothermal heat. After earlier attempts by previous developers to tap into hydrothermal resources encountered technical difficulties, Eavor took over the site with a different concept in mind, closed-loop geothermal.
Unlike traditional hydrothermal plants that rely on natural reservoirs of water and permeability, Eavor’s system, called the Eavor-Loop, functions more like a giant underground radiator. It consists of a closed system of horizontal and vertical wells connected to form a continuous loop. A working fluid circulates through this loop, picking up heat from the surrounding rock and transferring it to the surface, without bringing any subsurface fluids or gases into contact with the environment.
This technology sidesteps many of the risks and limitations that have historically constrained geothermal development such as induced seismicity, groundwater contamination and reliance on specific geological conditions. For Geretsried, it’s a second chance, this time with the benefit of data, technology and experience.
Engineering challenges and solutions
Drilling to depths of over 4500 metres presents enormous technical challenges, especially in a looped system that requires precision horizontal drilling, often through hard rock. The boreholes must remain stable under high temperatures and pressures, and they must be accurately aligned to meet at specific junction points underground.
Eavor has applied advanced directional drilling techniques, some of which are adapted from the oil and gas industry, to ensure the integrity of the boreholes. State-of-the-art telemetry systems monitor bit trajectory in real time, allowing for precise steering. In addition, the loop is designed to be self-sustaining. Once initiated, the thermosiphon effect, driven by temperature differences between the downhole and surface, keeps the fluid circulating without requiring pumps, reducing operational costs and complexity. Heat exchangers at the surface capture the thermal energy, which can be used directly for district heating or converted into electricity using binary cycle technology.
If the Eavor-Loop in Geretsried proves successful, it could serve as a model for replication across similar geologies worldwide. Closed-loop geothermal systems are modular and scalable, allowing them to be tailored for both urban and rural settings, from small heating plants to industrial-scale electricity generation.
As of 2025, the Geretsried project is moving into its construction phase with plans to begin full-scale operation. Once operational, it is expected to deliver up to 64 megawatts of thermal energy, enough to supply tens of thousands of homes with carbon-free heat. Moreover, it will do so with minimal environmental footprint and without fracking, water extraction or greenhouse gas emissions.
Geretsried offers more than just a case study. It shows how geology, drilling technology, thermodynamics and environmental stewardship can be made to work together. This is the kind of multidisciplinary thinking that will help tackle the energy challenges of this century.
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