Aerial view of the facilities at the Bouillante geothermal plant (Bouillante, Guadeloupe, 2011).
© BRGM
Faced with particularly acute challenges in terms of climate change and energy needs, the French Overseas Territories have remarkable and specific assets, enabling each of them to plan its specific transition path. For many of them, subsurface heat is among the assets that will enable them to achieve the government's objective of energy independence by 2050.
Following the adoption of Act No. 2023-175 on the acceleration of renewable energy production, the government asked for information on the current state of geothermal potential in the "Non-Connected Areas" of Guadeloupe, Martinique, Réunion, Mayotte and Saint-Pierre-et-Miquelon.
Non-Connected Areas (ZNI - Zones Non Interconnectées) are French territories that are not connected to the electricity grid in mainland France. These areas include Corsica and a number of overseas island territories, including those covered by this study.
Led by BRGM, one of the main bodies involved in the development of geothermal energy in these regions, this work has now been completed. The newly-published report takes stock of geothermal exploration and existing operations in these territories and, above all, sets out development prospects and recommendations in this field.
Guadeloupe: a showcase of a geothermal energy experiment that has already been successful, but is still in the making
The island of Guadeloupe not only has the only existing geothermal electricity generating facilities in the French Overseas Territories at the Bouillante site, but also considerable additional geothermal potential, particularly at this site. Its power station, commissioned in 1986 by EDF, currently has a production capacity of 15 MWe - soon to be increased to 25 MWe - and currently generates up to 110 GWh/year at a competitive rate. This already accounts for 5% to 6% of the island's annual electricity consumption.
The future of geothermal energy here is very promising, with more than 50 MWe expected to be added over the next decade. This will enable the island to meet almost 30% of its annual electricity needs. In addition, other areas around La Soufrière could be of interest from a geothermal perspective.
Martinique, Réunion and Mayotte: untapped potential
The islands of Martinique, Mayotte and Réunion also offer undoubtedly significant potential, which merits greater efforts to characterise them, in particular through exploratory drilling. For the first two, several deep drilling sites have already been proposed; on Réunion, despite a history of exploration dating back to the 1980s, the areas of obvious interest have yet to be confirmed.
It is high time to make up for the lack of deep boreholes to confirm the results of our exploration work. Deep geothermal energy involves a degree of uncertainty: although the subsurface temperature is unquestionably favourable in the case of volcanic islands, the permeability of reservoirs and borehole water flow rates, and hence the usable geothermal potential, are difficult to predict. In order to enable more drilling, the report recommends, as a priority, simplifying administrative procedures for setting up projects and improving coverage of the inevitable financial risk involved. It is also essential to take all the societal, economic and environmental constraints into account at an early stage when planning geothermal energy projects and to predict and mitigate the natural and industrial risks.
Geothermal energy can be used for many purposes
There are many possible uses for geothermal resources: they can be harnessed to produce electricity when the temperature is very high – in which case they have the advantage of being a basic source of energy – but they can also be used more directly, in particular as an energy source for cooling, thermal spas, drying, etc., depending on needs. The government's ambition to have the French Overseas Territories lead the way in the energy transition through the development of renewable energy sources puts BRGM's expertise back on centre stage, in conjunction with all the partners and stakeholders involved.
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