The Celtic Interconnector project marks a significant milestone in European energy cooperation, with two massive 230-ton transformers arriving at La Martyre in Finistère, France on May 28, 2025. This groundbreaking infrastructure will soon enable electricity exchanges between France and Ireland, strengthening the European energy grid and supporting renewable energy development across the continent.
Strategic energy connection between France and Ireland
The Celtic Interconnector represents a crucial link in Europe’s energy strategy, creating the first direct electricity connection between France and Ireland. The project centers around an ambitious technical solution that will allow both countries to share up to 700 megawatts of power – enough to supply approximately 450,000 households.
At the La Martyre site in Finistère, dozens of workers are busy installing two enormous transformers that recently arrived from Austria. These sophisticated units, along with two additional transformers expected soon, will perform the essential task of converting energy from direct current to alternating current. This conversion process is fundamental to connecting the Irish electrical network with the French and broader European grid.
Bertrand Hévin, responsible for stakeholder consultation for the Celtic Interconnector project at RTE (France’s transmission system operator), explains: “This interconnection will allow the European network to benefit from Ireland’s extensive wind energy and renewable development plans.”
The strategic benefits of this connection extend in both directions:
- France and Europe gain access to Ireland’s growing clean energy capacity
- Ireland secures its electrical supply with connection to the continental grid
- Both regions enhance energy resilience during peak demand periods
- The connection facilitates greater integration of renewable sources
- Energy prices may stabilize through increased market competition
Technical challenges of a 575-kilometer submarine connection
Creating an energy highway beneath the Celtic Sea presents remarkable engineering challenges. The Celtic Interconnector requires laying 575 kilometers of specialized cables, with approximately 500 kilometers running along the seabed between the two countries.
Construction at the La Martyre conversion station began less than two years ago, with completion expected by summer 2026. The civil engineering operations in Ireland have already concluded, while French land-based work stands at approximately 50% completion. The entire project, including the critical submarine component, aims for completion by late 2026.
The marine cable installation process, scheduled to begin later in 2025, involves specialized vessels and underwater technology. “Ships will lay the cables using submersible robots that guide precise placement on the seabed,” details Bertrand Hévin from RTE.
The installation method varies depending on seabed composition:
| Seabed Type | Installation Method | Protection Approach |
|---|---|---|
| Sedimentary | Trenching | Buried within seafloor |
| Rocky | Surface laying | Covered with rock protection |
This careful approach ensures environmental protection while maintaining compatibility with fishing activities in the deployment zones. The rock protection method specifically allows trawlers to continue operating in areas where cables cross rocky terrain.
Timeline and implementation schedule
The project follows a carefully orchestrated timeline, with several key phases overlapping to ensure efficient completion:
- Converter station construction (2023-2026)
- Land cable installation in Ireland (completed)
- Land cable installation in France (50% complete)
- Marine survey operations (completed)
- Submarine cable laying (starting 2025)
- System testing and commissioning (late 2026)
With final works projected to conclude in late 2026, the Celtic Interconnector should become operational in early 2027, opening a new chapter in European energy integration.
Expanding Europe’s energy integration network
The Celtic Interconnector doesn’t exist in isolation but forms part of a broader European strategy to create a more integrated and resilient energy network. Similar interconnection projects are currently advancing between France and several neighboring countries, including Spain, Italy, and the United Kingdom.
These connections reflect Europe’s commitment to energy transition, allowing regions with different energy production profiles to complement each other. For instance, during peak wind production in Ireland, excess power can flow to Continental Europe, while during shortfalls, Ireland can draw on French nuclear capacity or other European sources.
The European Union has recognized the Celtic Interconnector as a Project of Common Interest, highlighting its strategic importance for energy security and climate objectives. This designation has helped secure financing and coordinate the complex international aspects of the project.
By strengthening connections between previously isolated or weakly connected networks, Europe moves closer to a truly integrated energy market. This infrastructure supports the ambitious renewable energy targets established under the European Green Deal while providing practical mechanisms for countries to support each other during energy challenges.
When operational in 2027, the Celtic Interconnector will symbolize concrete progress toward a more connected, sustainable European energy future—one submarine cable at a time.
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