French geothermal energy: breaking down the barriers to high value-added energy

Still marginal in France, where it represents only 5% of heat production[1], it is nevertheless a key vector of the energy transition. While it has already established itself in certain geographical areas with conclusive results, other suitable areas remain unexploited, even though expert and recognized mastery of the technology is ready to be deployed. France must take advantage of its achievements in this area and seize more firmly the opportunity offered by its geological heritage to strengthen its energy sovereignty and accelerate its decarbonization. Analysis with Caroline Guion, head of the Geothermal division of heat networks at ENGIE Solutions.

A dormant energy source in territories to be conquered

Geothermal energy has already proven itself in areas with known potential, which already offer solid references in this area. The core activity has developed in Île-de-France thanks to the Dogger[2] and in the Aquitaine Basin where deep geothermal energy heats more than a million people.

Concrete facilities managed by ENGIE Solutions provide characteristic and successful examples of the use of this renewable energy. In the Paris Basin, we can notably mention the geothermal power plant at Champs-sur-Marne (Seine-et-Marne), which supplies 82% of the GéoMarne urban heating network. In Aquitaine, in Bordeaux, the Grand Parc Energies and Plaine de Garonne Energies heating networks, among others, offer an energy mix based primarily on geothermal energy at 86% and 80%. Geothermal energy has indeed provided a response to the decarbonization ambitions of these areas by providing virtuous heat to homes, public and tertiary buildings, and industrial sites.

However, deep geothermal energy is still underexploited in certain favorable areas whose probable geothermal resources must be exploited. These include Bresse, on the edge of Switzerland, and Hainaut, in the Hauts-de-France region, which offer a favorable geological context.

Questions and preconceived ideas persist regarding the impact of investigation campaigns in areas where the technology has not yet been installed, particularly regarding seismic risk control or the effects of drilling on groundwater. Implementing a scrupulous methodology and surrounding oneself with the best experts in the various fields involved therefore appear to be key elements in overcoming these presumptions weighing on geothermal energy, removing obstacles and increasing its acceptability.

Optimal supervision based on multiple expertise

The proven methods applied to geothermal energy, which are based on the audit of a large panel of experts and on R&D partnerships with major research institutes, demonstrate that nothing is left to chance during the operations carried out.

It is in fact through a "step-by-step" methodology that we proceed, with the help of continuous supervision during investigations which continues during operation. This real-time monitoring makes it possible to reduce risks and prevent the occurrence of incidents by accurately assessing the hazard.

The expertise mobilized demonstrates these precautions taken in this area and the rigor placed on environmental diagnosis. A whole panel of experts examines the projects for a 360° audit. Ecologists, acousticians, civil engineering experts carry out a thorough and exhaustive environmental impact study while modeling and drilling specialists, financial experts, geological insurers, academics and geophysical study firms are on hand to conduct a techno-economic study on each project. The assurance of the feasibility and environmental viability of the project must therefore be demonstrated to be validated by SAF-Environnement[3], the EIB[4], insurers and the relevant government services.

Let's add that each project requires a tailor-made implementation based on the territory concerned. While part of the methodology is replicable, the geological resource is always unique. This therefore requires essential adaptation to the specific characteristics of each area, as was the case for the Toulouse Metropolis, which relied on deep geothermal energy to expand its heating and cooling network after a detailed analysis of existing local and regional data supported by a seismic acquisition. Deep geothermal energy is also expected to soon cover 32% of the heating needs of the network in Aix-en-Provence, a pioneering city in this field. Choosing an energy mix combining geothermal and biomass will ensure a 59% reduction in pollutants compared to a 100% biomass project. We can also mention the towns of Bois-d'Arcy, Fontenay-le-Fleury and Saint-Cyr-l'École, in the Yvelines, which have also been pioneers with the filing of a geothermal research permit for their three municipalities to assess the geothermal potential of the subsoil, never before explored so far west of Paris, for the creation of a future heat network.

It also seems essential to demonstrate the greatest transparency towards communities and citizens on these projects. It is only by circulating information, data collected by studies and by organizing times for exchanges with the public, over time and with sincerity and the greatest openness, that we, the stakeholders in the sector, will be able to enrich the projects in the general interest and demystify preconceived ideas about geothermal installations.

Finally, one of the great strengths of these projects also lies in their ability to fuel fundamental research. As such, preliminary investigations are never carried out "for nothing" since they contribute to a better understanding of the French subsoil. Beyond the research programs implemented for each project, ENGIE Solutions is more broadly involved in collaborative R&D programs on geothermal energy. For example, a partnership was signed at the end of 2024 with Stadwerke München, a district heating operator in Munich. The objective of this cooperation, focused on deep geothermal operations and deep reservoir heat storage, is to benefit from mutual industrial feedback on similar geological basins in Paris and Munich. The SAPHEA project, for its part, brings together a consortium of French, Italian, German, and Austrian experts to create a European platform dedicated to the development of geothermal energy.

While these initiatives, specific to project leaders, constitute an initial lever to support geothermal energy, their effectiveness remains conditional on a change in the regulatory framework.

Towards a strengthening of regulatory competition as a lever

National aid for geothermal energy is mainly provided by ADEME and the geothermal guarantee fund[5], but its impact is limited by the lack of specific support in areas with potential. Regulatory complexity lengthens processing times and slows down the sector. It is therefore essential to simplify regulations and increase the human resources dedicated to processing applications. Finally, better consultation with field experts would make it possible to align theory and practice to achieve the objective of doubling geothermal projects by 2030.

In any case, the overhaul of the guarantee funds must be better aligned with the needs of operators and give impetus to the deployment of geothermal energy in favourable areas that remain to be explored. The core of the recommendations of a flash mission on the consequences of deep geothermal energy[6] focuses on strengthening the acceptability of geothermal energy and its regional deployment. The observation is unequivocal: geothermal energy is an "energy source that is still too little known to the general public or, unfortunately, well known to its detriment"[7].

Tribune by Caroline Guion, head of the Geothermal division of heat networks at ENGIE Solutions (LinkedIn).

[1] Ministry of Ecological Transition and Territorial Cohesion, Key figures for renewable energies, 2024 edition, www.statistics.developpement-durable.gouv.fr.

[2] The Dogger is the main aquifer exploited in the Paris region, located between 1.500 and 2.000m deep. It is the most exploited aquifer in Europe.

[3] Subsidiary of the Caisse des Dépôts et Consignations responsible for implementing and managing the Geological and Geothermal Risk Guarantee Funds by the public authorities.

[4] European Investment Bank.

[5] Administered by SAF-Environnement.

[6] Flash mission carried out in March 2024 by the parliamentary committee on sustainable development and regional planning.

[7] Quotes from MP Vincent Thiébaut, co-rapporteur of the flash mission. Summary available on www.assemblee-nationale.fr.