The Soultz-sous-Forêts site is the world's only operational pilot plant producing electricity via EGS technology (Enhanced Geothermal Systems) (NE France, 2005). © BRGM

Deep geothermal energy : the Soultz-sous-Forêts site has reached the sustainable production phase

Geothermal energy from deep fractured rocks could be one solution to the global challenge of meeting needs for non-polluting and renewable energy. This pilot operation, comprising an initial 1.5 MWe module developed at Soultz-sous-Forêts (Alsace) and in production since autumn 2010 (a world first), points to its feasibility.

The surface geothermal energy installations for this scientific pilot project that began some 20 years ago and is the only one of its kind in the world, have now been supplying power continuously to the grid for a year, following the introduction of the new feed-in tariff in July 2010.

A unique pilot in the world for deep geothermal energy

This pilot project, which draws on heat sources (up to 200°C) 4500 to 5000 m in depth, operates on a binary cycle principle (ORC: Organic Rankine Cycle): the hot fluid arriving at the wellhead circulates in a closed loop and passes through a heat exchanger, which transfers the calories to another organic fluid with higher-performance properties allowing it to drive a turbine.

Next objective: to determine the sustainability of Soultz-sous-Forêts operation

After contributing to scientific work on well stimulation with a view to developing the site, in parallel with its operation by the European Economic Interest Group (EEIG) on Heat Mining, BRGM is now conducting work financed by ADEME on the sustainability of the operation. The aim is to identify the circulation routes between the wells (by improving tracer tests and circulation modelling) and understand how they evolve during operations.


The surface installations at the pilot energy recovery plant at Soultz-sous-Forêts (Alsace). © GEIE Exploitation minière de la chaleur

Fundamental experimental scientific work

The work conducted at the Soultz site is supported by more fundamental experimental scientific work to understand the role of the interaction between the fluids transporting the calories and the rock environment, particularly in terms of changes in the permeability of the underground fracture network. A cell for examining thermo-hydro-mechanical and chemical couplings was specially built and put into operation at the ANTEA geo-mechanics laboratory in Orleans.

First fallout : new geothermal projects

Spin-offs from the technology now in operation at Soultz already include geothermal heat extraction projects for direct use in industry and combined heat and power projects.


“The aim of the Soultz project was to demonstrate the feasibility of the underground heat exchanger and show that the site is able to produce electrical power and to supp ly it continuously to the grid. It has now reached a decisive phase.”

Sylvie Gentier, project manager and research correspondent with the Geothermal Energy Division.

Sylvie Gentier “The aim of this deep geothermal energy extraction project using enhanced geothermal system (EGS) technology was to demonstrate the feasibility of the concept and show that the site is able to produce electrical power and supply it continuously to the grid.

Now we need to determine the operational lifetime of this type of installation and identify what problems can occur during operations. As soon as we can show that the site can operate permanently, other operations could be planned in other locations for power generation on a larger scale.

In parallel, thanks to improvements in the performance of heat exchangers and thermodynamic cycles, we have found that power can be generated at a temperature of less than 200°C. From the experience gained, we have good reason to expect the development of CH P (combined heat and power) systems that could also meet local demand for heat, particularly from industries. These more decentralised applications could be considered within the next 5 to 10 years.

Finally, understanding the subsurface environment at Soultz, where hot fluids circulate, allows us to work on reducing the geological risks, which are a critical issue in this type of operation, with a view to operating future sites from more closely targeted boreholes, which would also reduce the cost”.

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