Tonn Nua (Maritime Area A) Grid Connection is the transmission infrastructure programme being delivered by EirGrid to export approximately 900 MW of generation from the Tonn Nua / Helvick Head offshore wind development into Ireland’s onshore transmission network. The scheme comprises two offshore...
EirGrid plans to commence a second phase of geophysical surveys for the Tonn Nua (Maritime Area A) grid connection as part of its 2026 survey campaign, scheduled between April and September 2026. These surveys will further investigate offshore cable route options and areas around planned offshore substation locations to refine the transmission design and ensure environmentally appropriate routing.
For 2026, EirGrid has scheduled geotechnical surveys in support of the Tonn Nua (Maritime Area A) grid connection, to be carried out during a survey campaign planned from April to September 2026. These geotechnical investigations will characterise seabed and sub‑seabed conditions along shortlisted export cable routes and at offshore substation sites to inform detailed engineering of the HVAC 220 kV transmission system.
EirGrid intends to begin unexploded ordnance (UXO) survey activities for the Tonn Nua (Maritime Area A) grid connection as part of its 2026 survey campaign, expected to run between April and September 2026. The UXO surveys will assess and, where necessary, clear potential munitions hazards along the proposed offshore cable corridors and around offshore substation locations prior to later construction stages.
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Tonn Nua Maritime Area A offshore grid connection, Tonn Nua offshore wind grid connection, Powering Up Offshore – South Coast Tonn Nua grid connection, Tonn Nua (Maritime Area A) HVAC 220 kV connection
From April 2026, EirGrid plans to continue its onshore and offshore survey campaigns for the Powering Up Offshore – South Coast Tonn Nua grid connection, focusing on Landfall Zones C in County Cork and F in County Wexford. This 2026 campaign, scheduled to run between April and September, will build on 2025 results to further assess landfall and cable route options and provide additional environmental and site data needed to select the best-performing transmission corridors.
By 2025, EirGrid had commenced Step 4 optioneering works for the Powering Up Offshore – South Coast / Tonn Nua grid connection, using the Step 3 Consultation & Engagement Report and other inputs to narrow down grid infrastructure zones and potential landfall areas. This Step 4 phase focuses on identifying the best performing landfall options and cable route options to connect the Tonn Nua offshore substations into new onshore substations and loop‑in points on the existing 220 kV network.
The Maritime Area Regulatory Authority (MARA) approved a Maritime Usage Licence (MUL) for EirGrid, authorising marine and coastal survey activities from Maritime Area A (Tonn Nua) along Ireland’s south coast. This permit enables EirGrid, as transmission system operator, to carry out extensive geophysical, environmental, metocean and intertidal landfall investigations to define export cable corridors and offshore substation locations for the Powering Up Offshore – South Coast / Tonn Nua (Maritime Area A) grid connection.
In 2025, the CRU issued its Phase 2 Offshore Wind – Grid‑related Information decision (CRU/2025/13), setting the framework for calculating onshore connection asset costs for Phase 2 offshore projects. EirGrid used this decision to determine that the onshore connection assets for the Tonn Nua grid connection, to be owned by ESB Networks, have a total regulated cost of €53.323 million, which forms the basis for the connection charging arrangements for the project.
In December 2025, the CRU published its PR6 Final Determination, establishing a new offshore regulatory framework and revenue allowances for EirGrid for 2026–2030. This decision underpins EirGrid’s ability to advance its offshore transmission programme, including the Powering Up Offshore – South Coast initiative and the Tonn Nua (Maritime Area A) grid connection, by providing regulatory certainty and performance incentives for delivering offshore grid infrastructure.
By late 2025, EirGrid had completed the first phase of marine and coastal surveys for the Tonn Nua (Maritime Area A) grid connection, including extensive offshore geophysical data acquisition. Over the 2025 campaign, approximately 3,770 kilometres of seabed were surveyed under EirGrid’s Offshore Marine Survey Framework to characterise potential export cable corridors and inform design of the offshore transmission infrastructure.
During 2025, EirGrid completed Phase 1 of its marine and coastal survey campaign for the Powering Up Offshore – South Coast Tonn Nua project, finalising environmental, metocean and intertidal landfall field surveys related to the grid connection. The 2025 campaign, involving over 40,000 man‑hours and coordination with fisheries, industry and local communities, provided early insights to guide cable routing, landfall selection and offshore substation siting, while long‑term MetOcean buoy measurements continue to support ongoing planning.
By December 2025, EirGrid had published its Step 3 Consultation & Engagement Report and commenced Step 4 optioneering activities for the Powering Up Offshore – South Coast project, focusing on the Tonn Nua (Maritime Area A) grid connection. These Step 4 works aim to narrow down grid infrastructure zones and landfall areas in Cork and Waterford/Wexford, using survey data and stakeholder input to refine the design of the offshore and onshore transmission assets required to connect the 900 MW Tonn Nua offshore wind capacity to the national grid.
On 22 October 2025, MARA issued a Supporting Entity Multi Party Guarantee Template specifically for the Tonn Nua MAC. This template sets out how multiple supporting entities can guarantee payment of MAC levies up to commercial operation or build completion, providing the financial assurance framework that will apply to both the wind farm developer and EirGrid for the Tonn Nua offshore grid connection infrastructure within the maritime area.
On 5 September 2025, the Maritime Area Regulatory Authority (MARA) published a draft Maritime Area Consent (MAC) for Tonn Nua together with related supporting documentation, including a draft Supporting Entity Guarantee template and a draft form of opinion on that guarantee. These draft instruments outline the technical, legal and financial requirements that will apply to MACs for both the Tonn Nua offshore wind array and EirGrid’s associated transmission and cable infrastructure within Maritime Area A.
Following the award of a Maritime Usage Licence by MARA, EirGrid commenced Phase 1 marine and coastal surveys for the Powering Up Offshore – South Coast Tonn Nua grid connection in July 2025. This campaign initiated extensive offshore geophysical investigations across potential export cable route corridor options from Maritime Area A (Tonn Nua) as part of defining transmission routes and offshore substation locations.
In July 2025, alongside geophysical work, EirGrid began a broader Phase 1 marine and coastal survey programme for the Tonn Nua (Maritime Area A) grid connection, including environmental and metocean investigations and non-intrusive intertidal landfall studies. The programme also involved deploying two MetOcean buoys to collect long‑term data on waves, water quality, wind and sunlight to inform offshore planning and environmental assessment for the transmission infrastructure.
On 24 June 2025, EirGrid issued Version 2 of the ORESS Tonn Nua Grid Connection Information Pack for the Tonn Nua (Maritime Area A) grid connection, setting out the Offshore Generator Transmission Use of System (OG-TUoS) charge applicable to the project. The document specifies that, in line with the CRU’s Phase 2 Offshore Wind – Grid Connection Charging Policy, Tonn Nua will pay a fixed OG-TUoS of €13.9550 per kW per month for a 30‑year period, with payments commencing once the grid delivery milestone is achieved and an Interim Operational Notification has been issued. This establishes the regulated revenue regime for the TSO‑owned offshore transmission assets serving the 900 MW Tonn Nua development.
On 24 June 2025, EirGrid’s updated ORESS Tonn Nua Grid Connection Information Pack confirmed that the total cost of the onshore connection assets for the Tonn Nua (Maritime Area A) grid connection, which will be owned by ESB Networks, is €53.323 million. The pack details a staged payment schedule for the Tonn Nua offshore wind farm developer, including a non‑refundable first stage payment of €9 million prior to execution of the Connection Agreement, followed by four further payments linked to the Consents Issue Date, and requires the developer to provide a Connection Charge Bond of €15.9969 million as security for the connection charge. These arrangements define how the onshore grid connection infrastructure for Tonn Nua will be funded and recovered from the project.
On 24 June 2025, EirGrid published Version 2 of the ORESS Tonn Nua Grid Connection Information Pack, updating the indicative HVAC connection design for the 900 MW Tonn Nua grid connection and adding confirmed charging information. The pack specifies the 900 MW split via new 220 kV connecting stations in Cork and Wexford, a firm connection method looping into existing 220 kV circuits at Aghada–Knockraha and Great Island–Lodgewood/Great Island–Kellis, total onshore connection asset costs of €53.323 million, a monthly Offshore Generator Transmission Use of System (OG‑TUoS) charge of €13.9550/kW over 30 years, staged connection-charge payments, and a target Grid Delivery Date of 1 July 2033.
On 2 April 2025, EirGrid issued Version 1 of the ORESS Tonn Nua Grid Connection Information Pack to all prospective ORESS Tonn Nua bidders, outlining the indicative HVAC grid connection method for the 900 MW Tonn Nua project, including a 450 MW export to the Cork area and 450 MW to the Waterford/Wexford area via new 220 kV infrastructure and offshore/onshore cables. The document made clear that the connection design and associated terms were indicative, for information purposes only, and subject to change during the later connection offer process.
In 2025, under its Offshore Marine Survey Framework for the Powering Up Offshore – South Coast / Tonn Nua grid connection, EirGrid engaged Fugro as lead contractor, supported by TechWorks Marine and Green Rebel, to deliver the first phase of marine and coastal surveys along Ireland’s south coast. The contracted campaign covers geophysical, environmental and metocean investigations across potential export cable route corridor options from Maritime Area A (Tonn Nua), as well as intertidal landfall studies, providing essential data to shape the design and routing of the transmission infrastructure that will bring 900 MW of offshore wind power ashore.
In 2024, the Commission for Regulation of Utilities (CRU) issued Direction CRU/2024/124, which sets out conditions for EirGrid to issue a grid connection offer for the Tonn Nua offshore wind facility. The direction requires the ORESS Tonn Nua auction winner to submit an ORESS Tonn Nua Notice of Award to EirGrid within three calendar months of receiving it, creating a formal regulatory linkage between the support scheme outcome and the transmission connection offer for the Tonn Nua grid connection.
In November 2024, EirGrid completed its Step 3 "Emerging Best Performing Options" work for the Powering Up Offshore – South Coast / Tonn Nua grid connection, publishing a report that evaluated and short‑listed landfall zones and grid connection zones for bringing approximately 900 MW from Maritime Area A (Tonn Nua) into the onshore 220 kV network. This engineering and optioneering phase refined cable route corridor options and potential substation locations in Cork and Waterford/Wexford for further assessment in Step 4.
EirGrid conducted a Step 3 public consultation for its Powering Up Offshore – South Coast programme focused on the Tonn Nua (Maritime Area A) grid connection, inviting feedback on emerging best-performing landfall zones and grid connection options. The consultation outcomes were documented in a Step 3 Emerging Best Performing Options Report and a Step 3 Engagement and Consultation Report dated November 2024, which inform subsequent optioneering of grid infrastructure zones and landfall areas.
On 30 October 2024, Ireland’s Department of Climate, Energy and the Environment (DECC) published the ORESS Tonn Nua auction Terms and Conditions. These terms govern the Offshore Renewable Electricity Support Scheme (ORESS) competition for Tonn Nua and establish the requirement that the successful bidder submit an ORESS Tonn Nua Notice of Award to EirGrid within three months in order to receive a grid connection offer for the Tonn Nua offshore wind facility and associated transmission connection.
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