The Celtic Interconnector is a planned 700MW high-voltage submarine power cable that will link the southern coast of Ireland and the northwest coast of France. (Credit: © Siemens Energy)
France and Ireland sign key agreements for the project. (Credit: European Commission)
Nexans plans to utilise its Aurora Cable Laying Vessel for laying cables for the project. (Credit: © COPYRIGHT NEXANS 2018)

Celtic Interconnector is a planned 700MW high-voltage subsea power cable that will connect the southern coast of Ireland and the north of France.

The High Voltage Direct Current (HVDC) connector will travel 575km from East Cork to the northwest coast of Brittany, enabling transmission of enough electricity to power 450,000 homes.

The project is being developed and co-funded by Ireland’s state-owned electric power transmission operator company EirGrid and its French counterpart Réseau de Transport d’Électricité (RTE).

Celtic Interconnector has also received significant funding from the European Union (EU).

The project is estimated to cost around €1.6bn and reach operational status by 2026. Once complete, it will become Ireland’s first interconnection with mainland Europe.

Project Development

The Celtic Interconnector is expected to facilitate the development of an integrated energy system for the European energy market and expedite energy transition.

EirGrid took a six-step approach to develop the project.

Since 2012, RTE and EirGrid undertook technical and environmental studies to confirm the technical feasibility of a DC submarine and land circuit between France and Ireland.

It was recognised as a project of common interest (PCI) by the EU in October 2013. The recognition allowed the Celtic Interconnector to benefit from improved regulatory conditions and EU financial assistance from the Connecting Europe Facility (CEF).

In January 2018, EirGrid submitted an application for a Foreshore License to the Department of Housing, Planning and Local Government in Ireland to evaluate the subsea cable route and landfall options.

In 2019, the company launched consultations to shortlist landfall locations and zones for a convertor station. In the same year, the European Commission also agreed to provide €530m funding for the Celtic Interconnector.

This was followed by an online consultation on the project in the UK in 2020 as part of PCI process.

In July 2021, EirGrid submitted a planning application to Ireland’s national independent planning body An Bord Pleanála for the Irish on-shore element of the interconnector.

In May 2022, the project received approval from An Bord Pleanála, subject to certain approvals. It was followed by Foreshore Licence in Ireland in August 2022 and marine licence in September 2022.

In November 2022, EirGrid and RTE signed key technical and financial agreements for the Celtic Interconnector thus advancing the project development to Stage 6.

This stage, which involves Construction, Energisation and Benefit Sharing, is scheduled to take place from 2022 to 2026.

Additionally, agreements were signed for €800m financing from the European Investment Bank, Danske Bank, Barclays and BNP.

Design details

The Celtic Interconnector will link the commune of La Martyre in Brittany, France, to the village of Knockraha in County Cork, Ireland.

Around 500km of the 575km-long electricity highway will run through the Celtic Sea.

The key components of the Celtic Interconnector infrastructure will include the converter stations; the Alternating Current (AC) Land Circuit (underground cable); the Direct Current (DC) Land Circuit (underground cable); the landfall points; and the subsea cable.

Although the French and Irish electricity systems use High Voltage Alternative Current (HVAC) technology, the electricity will be transferred across the connection using High Voltage Direct Current (HVDC) technology, an industry standard for long distances.

The convertor stations at the two terminal points will again convert HVDC to HVAC and feed it to the respective networks.

The interconnection will utilise HVDC 320kV technology. The overall route will include around 500km of subsea cable; a 40km underground route in Brittany, France; and a 35km underground route in Cork County, Ireland.

A 10km long 400kV HVAC connection to the Irish grid will also be built as part of the project.

The project will also include a fibre optic link along the route for operational control, communication and telemetry purposes.

Route details

The interconnector will have two substations- Knockraha in Ireland and in La Martyre in France.

In Ireland, the onshore infrastructure of the project will include a 220kV AC underground connection between the Knockraha substation and a new proposed converter station and an underground DC connection to the landfall point on the Irish coast to connect with the subsea link.

The 500km long subsea connection will pass to the west of the Isles of Scilly to connect link the Ceinture Dorée (Gold Belt) coast in Brittany.

The preferred route for the cable was identified following detailed physical marine surveys to minimise environmental and maritime impact. The submarine cable will be either buried underground or will be laid on the seabed with a protective covering.

After the subsea cable makes landfall, an underground cable will connect it to the converter station.

In France, the onshore infrastructure for the interconnector will include an underground DC connection between the French coast and the converter station and a 400kV AC underground connection to the La Martyre substation.

Contractors involved

In November 2022, Siemens Energy secured a ‘mid three-digit million-euro range’ contract to deliver the HVDC transmission technology for the Celtic Interconnector. The contract works will include building converter stations in Ireland and France.

French cable manufacturer Nexans received the contract to design and install the 575km subsea cable for the project.

Nexans’ facilities in Halden (Norway) and Charleroi (Belgium) will manufacture the subsea and underground cables, respectively. The company will utilise its Aurora Cable Laying Vessel for laying subsea cables.

EirGrid Group and RTE contracted Wood for subsea engineering services for the Celtic Interconnector project. This included marine engineering studies for the design of a subsea power cable system, and technical project management services.