Irish offshore wind grid takes shape after 70,000-hour survey

Ireland has completed a major stage in planning the transmission infrastructure needed to bring offshore wind power ashore, with grid operator EirGrid concluding a marine and coastal survey campaign involving almost 70,000 hours of work across 2,337 kilometres of sea.

The investigations will inform engineering, environmental and planning assessments for the Powering Up Offshore – South Coast programme, which aims to connect the planned 900MW Tonn Nua offshore wind farm and potentially other projects to Ireland’s national electricity grid.

Tonn Nua is the first area being progressed under the government’s South Coast Designated Maritime Area Plan, which identifies four areas for potential offshore wind development.

The project, off County Waterford, was awarded to Helvick Head Offshore Wind DAC, a joint venture between ESB and Ørsted, following Ireland’s second offshore wind auction in November 2025. It has a target capacity of 900MW.

“The surveys provide vital information that will help us better understand the marine and coastal environment,” said Adam Cronin, EirGrid’s Head of Offshore – South Coast.

Substations and cable routes take shape

EirGrid’s plans include two offshore substation platforms, subsea transmission cables linking them to landfall locations, new onshore substations and connections into the existing transmission network.

Underground cables would carry electricity from the coastal landfalls to the new substations, with further connections to the national grid using underground cables or overhead lines.

Determining where this infrastructure can be built requires detailed knowledge of seabed conditions, coastal geology, marine ecology and environmental constraints. Geophysical, geotechnical and environmental investigations help engineers assess the feasibility of different routes and construction locations before preferred options are selected.

EirGrid is currently at Step 4 of its six-stage project development process, which focuses on identifying where infrastructure should be put.

A public consultation launched on 15 September is seeking feedback on emerging options, including offshore substation zones, cable corridors, landfall locations and onshore transmission routes in Cork and Wexford. It is scheduled to close on 8 December 2026.

“We are encouraging people to take part in the current consultation and review the emerging options being presented,” said Cronin.

Major procurement package launched

Alongside the surveys, EirGrid is preparing engineering packages worth hundreds of millions of euros needed to deliver the new transmission system.

The scope includes the design, fabrication, installation and commissioning of offshore substations, associated high-voltage equipment, onshore compensation compound works and related engineering.

EirGrid chief executive Cathal Marley described the package as ‘a critical step towards a cleaner energy future’ and encouraged supply-chain companies to engage with the operator.

The works could create opportunities across offshore engineering, high-voltage equipment, marine installation, cable systems and port services.

The government aims to develop at least 5GW of offshore wind.

Minister of State Timmy Dooley has said Ireland is ‘moving towards a planned, long-term offshore sector’ government, industry, agencies and communities all involved.

The immediate task is to use the survey results and consultation responses to refine potential locations and routes before progressing towards planning.

The next steps are to turn the technical evidence into defined infrastructure proposals, secure approvals and move towards construction of the substations and cable connections that will bring offshore electricity ashore.