IN Brief:
- The 700MW Celtic Interconnector between Ireland and France is scheduled to commission in Q4 2028.
- Submarine cable installation remains on the critical path, with trenching now expected across substantially more of the route than originally planned.
- Ireland’s adequacy assessment remains tight through 2028, increasing scrutiny of further delays to new generation and interconnection.
Ireland’s energy minister is pressing EirGrid for greater clarity over delays to the Celtic Interconnector, as difficult submarine cable installation keeps the 700MW electricity link with France on a commissioning path towards the final quarter of 2028.
The revised timetable itself is not new: EirGrid already lists Q4 2028 as the expected commissioning period. Fresh scrutiny centres on why the programme has moved so far from earlier delivery assumptions, how much further schedule risk remains, and whether enough information has been provided to government as Ireland plans for a tight electricity adequacy position through the same period.
The €1.6bn interconnector will run for about 575km between east Cork and Brittany, including roughly 500km of submarine cable. It will become Ireland’s first direct electricity connection with continental Europe, using high-voltage direct current for the long-distance land and subsea sections before converter stations interface with the alternating-current transmission systems in Ireland and France.
Marine work has become the critical constraint. Current estimates indicate that trenching may be required across about 90% of the submarine route, compared with an earlier assumption of roughly equal use of trenching and faster jetting methods. That change increases the time required to bury and protect the cable and exposes the programme more heavily to vessel productivity, seabed conditions, equipment availability, and workable weather windows.
The latest installation schedule includes marine campaigns through 2028. EirGrid has reported continuing progress in French waters, but the remaining sequence leaves limited tolerance for disruption if trenching rates fall below plan or adverse weather reduces the usable offshore construction season.
Energy minister Darragh O’Brien has sought a fuller explanation from EirGrid about the changing programme and the information supplied to government. The concern extends beyond construction management because the Celtic Interconnector has become an input to Ireland’s wider security-of-supply planning.
EirGrid’s All-Island Resource Adequacy Assessment for 2026–2035 shows Ireland outside the reliability standard from 2026 to 2028 under both its base and secure assessments. The position improves as new capacity enters service, including Celtic from 2028, although the secure assessment remains tighter than the base case later in the study period.
That gives the commissioning date greater weight than a normal infrastructure milestone. An interconnector does not create domestic generation, but it provides access to additional electricity markets, creates another balancing route, and can reduce the amount of domestic generation required to cover every credible operating condition independently.
The link will also provide an export route when Ireland has surplus renewable output. As more wind and solar capacity connects, controlled cross-border transfer becomes increasingly valuable because production and demand do not always coincide within the national system. HVDC converters allow operators to set the direction and level of power transfer rather than leaving the flow primarily to network conditions.
Long submarine connections favour HVDC because alternating-current cables accumulate charging current over distance, reducing the proportion of cable capacity available for useful power transfer. Converter stations add substantial cost and complexity, but they make a 575km connection technically practical while giving the system operators controllable exchange between the two markets.
Celtic therefore depends on a complete chain of infrastructure operating together. Submarine and underground cables, converter stations, protection systems, controls, telecommunications, and the Irish and French grid connections all have to be commissioned as an integrated system before the interconnector can enter commercial service.
Substantial onshore work has already progressed. In Ireland, the route connects Knockraha substation with the converter station at Ballyadam before continuing underground to Claycastle Beach in Youghal. France has its own converter and grid works, while offshore installation joins the two national sections across the Celtic Sea.
The European Commission awarded €530.7m of Connecting Europe Facility support to the project in 2019, reflecting its wider role in European electricity-market integration. The connection is expected to strengthen Irish security of supply, increase competition between markets, and support greater renewable generation on both sides of the link.
Those benefits remain intact, but the construction sequence has become less forgiving. Additional trenching raises offshore working time without changing the finished interconnector’s capacity, so the engineering challenge is now dominated by execution rather than design ambition.
Further slippage would also arrive at an awkward point for Ireland’s capacity planning. EirGrid’s adequacy work already identifies delayed new generating capacity and the revised Celtic commissioning date among the reasons for increased stress through 2028. Temporary emergency generation can provide insurance against shortfalls, but it is not intended to meet permanent demand growth.
The immediate test is therefore whether the remaining marine campaigns can maintain the late-2028 programme. With EirGrid publicly committed to Q4 commissioning and government now asking harder questions about the route to that date, another material revision would carry consequences beyond the interconnector construction site.
