Palm trees in Grande Comore island, Comoros
In late 2023 and again in the summer of 2024, Steam Srl (STEAM) completed two assignments to de-risk the Mount Karthala Geothermal Project in the Comoros. Commissioned by the Bureau Géologique des Comores (BGC) and supported by the United Nations Development Programme (UNDP) Comoros and UNDP Rome Centre for Climate Action and Energy Transition, the project has the potential to become the first geothermal power plant in the Comoros, and to make the Comoros the third African nation with an operational geothermal power plant.
STEAM’s work confirmed the viability of the potential geothermal resource and then further confirmed the presence of sufficient groundwater near the drilling site to support both deep exploration activities and serve the island as a secure water source for the future. The project findings are expected to help unlock new investment for the Mount Karthala project, which has been in development since 2008.
Geothermal development in island nations: A strategic advantage
The Mount Karthala project is a significant development in the context of geothermal energy for island nations. Islands like the Comoros face unique energy challenges due to their reliance on imported fuels, which makes energy both expensive and vulnerable to supply chain disruptions. Geothermal energy offers a sustainable, locally sourced alternative that enhances both energy security and economic stability.
For the Comoros, developing its local geothermal energy resources could be transformative. Located in the Mozambique Channel, the country relies heavily on diesel generators and biomass for electricity and heating. With its volcanic activity, particularly around Mount Karthala, the Comoros holds significant untapped geothermal potential. The successful identification of groundwater resources as a drilling aid brings the country one step closer to realizing this potential, aligning with broader global goals of the energy transition such as the UN SDG 7 (Affordable and Clean Energy), and reducing carbon footprints.
The history of geothermal in the Comoros
The Comoros islands began their geothermal journey in 2008, when experts from Kenya Electricity Generating Company (KenGen) carried out geoscientific studies that confirmed the area’s geothermal potential. Six years later, the Bureau Géologique des Comores (BGC) conducted studies with the support of several consultants and service providers. The results indicated that the area has the potential to generate more than 45 MW of geothermal power.
Following the study, the Comoros secured commitments from Geothermal Risk Mitigation Facility (GRMF), the Global Environment Facility (GEF) and other donors and financiers to proceed with the exploratory drilling, paving the way for a financial close thanks to a business plan that outlined a clear path to profitability.
One of the greatest hurdles to making a convincing argument that the Mount Karthala project is viable rests in the ability to support exploratory drilling using ground water, with expected expected water supply needs of 3,000 liters per minute for 60 days. Although the Grande Comore Island is characterized by abundant rainfall of between 1,500 and 2,000mm/year, up to 4,000 mm/year in the Mount Karthala area, the infiltration rate is estimated around 95%, meaning much of the precipitation flows into the underground and not into the sea.
However, most of the country’s wells are near the shore, making it unfeasible to pipe water up to the drilling area. Consequently, it was necessary to investigate the hydrogeological setting of the inner zones of the volcanic units of Mount Karthala to provide the necessary water supply.
De-risking the reservoir model and the hydrological model
STEAM’s involvement in the Comoros project, together with its partner GEL Energy, was divided into two strategic phases. In the first phase, working in collaboration with UNDP Comoros and local stakeholders, STEAM’s team reviewed the existing resource assessments and project plan, and then developed a detailed roadmap for moving the project forward to the exploratory phase. In this phase, STEAM collaborated with Geothermal Engineering Ltd, the experts in project development and funding behind the successful United Downs geothermal project implemented in Cornwall (UK).
In the second phase, STEAM geologist Lorenzo Favaro worked with Viridien Group and Phoenix Geophysics to execute a two-week capacity building agenda and hydrogeological study. This phase confirmed the validity and integrity of the field testing instruments through a class and field training exercises for the BGC team.
Once adept in the use of the instruments, the project team executed an integrated magneto-telluric (MT) survey, which comprised an expanded field of 24 MT additional sites, extending the 3D resistivity model towards the northern area of the island. The expanded testing area aimed to expand the original model built by BGC in 2015, shifting the focus to the shallower layers on the northern side of the volcano in order to confirm the feasibility of shallow water wells, between 250 and 300m, foreseen in earlier studies.
The results of Phase 2 confirmed that it is reasonable to expect a water table depth of approximately 230-300 m g.l. in accordance with the original projections, though it also indicated that some wells would need to go deeper.
Expert insight from STEAM’s Senior Geologist
Lorenzo Favaro, STEAM’s Senior Geologist and lead for the project, emphasized the importance of a comprehensive approach in geothermal project development: “Acquiring new data in tropical forests and inaccessible areas was a unique and trying experience, with many hours of walking, even at night. But all data—geological, logistical, and environmental—contribute to de-risking a geothermal project.”
“A multidisciplinary company like STEAM, with our long and diverse experience, has the capability to work with all project stakeholders to build the complete datasets required to move past the surface exploration phase. Without this step, the deep exploration and subsequent design and construction phases of a geothermal plant are futile.”
