Reference, completed project

Geothermal potential of Non-Connected Areas (ZNI) in French overseas departments and territories

At the request of the General Directorate for Energy and the Climate (DGEC), on behalf of the Government and for the attention of Parliament, BRGM has drafted a report on the geothermal potential of Non-Connected Areas (ZNI) on the islands of Guadeloupe, Martinique, Reunion, Mayotte and Saint-Pierre-et-Miquelon.

14 October 2024

Bras de Benjoins thermal spring, Cirque de Cilaos, Reunion Island.

The need

The study was commissioned from BRGM by the DGEC. The objective is to address Article 107 of the act introduced to accelerate the production of renewable energies (drawn up by a Joint Committee): “The Government shall submit to Parliament a report on the geothermal potential of areas not connected to the grid (ZNI) in mainland France, particularly on Reunion Island.” In agreement with the DGEC, the scope of this study includes the volcanic islands of Guadeloupe, Martinique, Reunion and Mayotte. It also covers the specific case of the archipelago of Saint-Pierre-et-Miquelon, which is keen to study the possible use of geothermal energy for heat production.

The results

After outlining the different types of geothermal energy and the main goals of the Multiannual Energy Programmes (PPE) on each island, the study reviews the situation in terms of geothermal exploration and any existing operations. The main conclusions and recommendations show that:

Guadeloupe has the greatest geothermal potential. Bouillante has been producing geothermal electricity since 1986, but it is the only region to do so. The local power station has a production capacity of 15 MWe, soon to be increased to 25 MWe, and currently generates up to 110 GWh/year, around 6% of the island's annual electricity consumption. This makes the island one of the world's top 12 geothermal electricity producers.
None of the other ZNIs currently produce geothermal electricity, although extensive shallow geothermal exploration work has been carried out on the islands of Martinique and Reunion since the 1970s-1980s, and on Mayotte since 2005. In the case of Martinique and Mayotte, several sites have been suggested for deep exploratory boreholes. On Reunion Island, a number of areas of proven interest have been identified, with some still requiring further shallow exploration.
Although temperatures are high and fairly easy to assess on volcanic islands, it is difficult to predict reservoir permeability and borehole flow rates, and therefore equally difficult to establish exploitable geothermal potential.
Unlike Reunion Island and St-Pierre-et-Miquelon, the context in the French West Indies and Mayotte is not favourable to the development of shallow geothermal energy.

General view of the Bouillante high-temperature geothermal power plant in Guadeloupe

Using the results

The report from this study has been validated and approved by the DGEC and is due to be submitted to Parliament by the Government. In the case of Guadeloupe, the conclusions mention the ongoing substantial development of geothermal energy in the Bouillante region, with over 50 MWe of additional capacity by 2030-2035. This will already cover around 30% of the island's annual electricity needs, even without possible contributions from the Soufrière region. On the islands of Reunion, Martinique and Mayotte, it will be necessary to create more boreholes in addition to the five created since the 1970s, in order to validate (or not) the results of shallow exploration on the sites already selected.

In order to accelerate the development of geothermal energy in these ZNIs, the report recommends, as the main priority, to simplify administrative procedures for setting up projects and to better cover the financial risk of failing to find exploitable resources. It is also essential to take account at an early stage of the social, economic and environmental constraints, as well as natural and industrial risks, in order to ensure that geothermal energy projects are accepted by local populations and seen as contributing to the image of these regions as “unspoilt territories”. Alongside electricity production, it would be possible to develop other direct uses of the heat associated with geothermal systems of lower temperatures, which are also present in these regions.