Greenlink Interconnector: UK-Ireland HVDC Submarine Cable

Overview

Greenlink is a high-voltage direct current (HVDC) submarine power cable interconnector linking the electricity grids of Ireland and Great Britain. The infrastructure connects County Wexford in the Republic of Ireland with Pembrokeshire in Wales, establishing a critical north-west European energy corridor. Commissioned in 2025, the facility is currently operational and serves as a key asset for cross-border power trading and grid stability between the two nations. The project is operated by Greenlink Interconnector Limited, which manages the day-to-day technical and commercial functions of the link.

The interconnector features a total length of 190 km, with approximately 160 km of the route running subsea across the Irish Sea. The system has an installed capacity of 500 MW, enabling significant bidirectional power flows. This capacity allows for the export of Irish renewable generation, particularly wind power, to the British market, while also providing import capabilities to balance domestic demand and enhance frequency control on both sides of the sea. The HVDC technology chosen for Greenlink is well-suited for long-distance submarine transmission, offering efficient power transfer with relatively low losses compared to alternating current (AC) alternatives over similar distances.

Ownership of the Greenlink asset is held by a consortium comprising Element Power and Partners Group. Element Power, a specialist in European power transmission infrastructure, and Partners Group, a global alternative asset manager, jointly invested in the project to develop this strategic energy link. The collaboration between these entities facilitated the financing and construction phases, leading to the 2025 commissioning date. The interconnector represents a significant investment in the integration of the Irish and British power systems, contributing to the broader decarbonization goals of the region by enabling greater utilization of variable renewable energy sources.

Technical Specifications

Greenlink operates as a high-voltage direct current (HVDC) submarine interconnector, utilizing a symmetrical monopole configuration to transmit electricity between Ireland and Wales. The system is designed with a nominal power rating of 500 MW, enabling efficient bulk power transfer across the Celtic Sea. The DC voltage level for the link is specified as ±320 kV, a standard for modern HVDC point-to-point connections that balances insulation requirements and conductor sizing. The total length of the submarine cable route spans 190 km, connecting the landfall sites in County Wexford and Pembrokeshire. This configuration allows for flexible power flow direction, optimizing the integration of variable renewable energy sources on both sides of the interconnector.

The symmetrical monopole design involves two conductors carrying equal and opposite currents, with the return path often utilizing the sea water or a dedicated return cable, depending on the specific engineering choices for the route. This setup minimizes electromagnetic interference and optimizes the use of cable cross-sections. The ±320 kV rating indicates that each pole operates at 320 kilovolts relative to the midpoint or ground reference, providing a total potential difference that drives the 500 MW power flow. The 190 km length represents the physical distance of the submarine section, which is a critical factor in determining cable losses and voltage drop characteristics. Greenlink Interconnector Limited manages the operational parameters to ensure stability and efficiency across this cross-border link, which became fully operational in 2025.

Route and Infrastructure

The Greenlink interconnector utilizes a 190 km high-voltage direct current (HVDC) submarine power cable to link the electricity grids of Ireland and Wales. The physical route connects County Wexford in Ireland with Pembrokeshire in Wales, facilitating cross-channel energy transmission between the two nations. The infrastructure design incorporates specific landfall points and onshore connections to integrate with existing national grid assets.

Landfall Points

The Irish end of the interconnector lands at Baginbun Beach in County Wexford. This location serves as the primary entry point for the submarine cable into the Irish landmass. On the Welsh side, the cable makes landfall at Freshwater West beach in Pembrokeshire. These specific coastal locations were selected to optimize the subsea route length and facilitate connection to the respective national grid infrastructures.

Grid Connections

In Ireland, the onshore cable from Baginbun Beach connects to EirGrid’s Great Island substation. This substation is a key node in the Irish transmission network, allowing the imported power to be distributed across the country. In Wales, the cable from Freshwater West connects to National Grid’s Pembroke substation. This connection integrates the interconnector into the British transmission system, enabling power flow between the two markets.

Route Segments

Project History and Timeline

Greenlink’s development trajectory spans from initial subsea surveys in 2018 to full commercial operations in 2025. The project, operated by Greenlink Interconnector Limited, required extensive cross-border coordination between Ireland and Wales to establish a 190 km high-voltage direct current (HVDC) submarine link. Early phases focused on technical feasibility and environmental assessment, culminating in the 2018 subsea surveys that defined the cable route between County Wexford and Pembrokeshire.

Planning and Licensing

Stakeholder engagement intensified in 2019 with formal consultations aimed at securing local and regional support for the interconnector. These efforts informed the 2020 planning applications submitted to relevant authorities in both jurisdictions. The licensing process reached a critical milestone in 2021 when the UK marine licence was granted, clearing the way for construction in the Welsh section of the route. This period established the regulatory framework necessary for the project’s financial viability.

Construction and Commissioning

Financial close was achieved in 2022, triggering the official start of construction activities. This phase involved the manufacturing and laying of the HVDC submarine cables, as well as the development of onshore converter stations. By 2024, construction was completed and initial trials commenced to verify system performance under varying load conditions. The interconnector achieved full operational status in 2025, delivering its rated 500 MW capacity to the grid. The following table summarizes the key project milestones.

Why it matters

Greenlink represents a pivotal infrastructure development in the integration of the energy systems of the British Isles. As a 190 km long high-voltage direct current (HVDC) submarine power cable, it physically links County Wexford in Ireland with Pembrokeshire in Wales, creating a direct electrical bridge between two major national grids. The operational status of this interconnector, commissioned in 2025, marks a significant milestone for regional energy security and market efficiency. By connecting the EirGrid network in Ireland with the National Grid in Wales, Greenlink facilitates the seamless exchange of electricity across the Irish Sea, reducing reliance on domestic generation sources on either side of the water.

Strategic Capacity and Energy Security

The 500 MW capacity of Greenlink provides substantial flexibility for energy traders and system operators. This capacity allows for significant power flows during peak demand periods, helping to stabilize frequency and voltage across both networks. For Ireland, this connection offers a critical outlet for surplus renewable generation, particularly from wind farms in the east and south, while providing a backup source of power during periods of low wind or high domestic consumption. In Wales and the broader UK grid, Greenlink serves as a reliable import source, enhancing diversity in the generation mix and reducing the need for peaking plants. The HVDC technology employed is particularly suited for this submarine link, minimizing energy losses over the 190 km distance and allowing for precise control of power flow direction.

Regional Integration Context

Greenlink is one of the major interconnectors linking the British Isles, contributing to the broader strategy of creating a more cohesive European energy market. Its operation by Greenlink Interconnector Limited ensures specialized management of the cross-border asset, optimizing utilization rates and revenue sharing between the two jurisdictions. The interconnector supports the integration of variable renewable energy sources, which is crucial for meeting climate targets in both Ireland and the UK. By enabling the sharing of resources, Greenlink reduces the overall cost of system operation and enhances resilience against localized outages. This infrastructure underscores the strategic importance of cross-border cooperation in modern energy planning, demonstrating how physical connections can translate into economic and environmental benefits for both nations.

How does an HVDC interconnector like Greenlink work?

Greenlink operates as a high-voltage direct current (HVDC) submarine power cable, utilizing technology specifically optimized for long-distance subsea transmission. Unlike alternating current (AC) systems, which require synchronous rotation of generators on both ends and suffer from capacitive charging currents over long cable runs, HVDC allows for efficient power flow between asynchronous grids. The interconnector uses a symmetrical monopole configuration, a design choice that balances cost and reliability for the 190 km route between County Wexford and Pembrokeshire. This configuration employs two conductors operating at opposite polarities, specifically ±320 kV, with the return path often completed through the sea water itself or a dedicated return conductor, depending on the specific engineering design of the monopole system.

Efficiency over Subsea Distance

The selection of HVDC technology is critical for the 190 km span of the Greenlink cable. In AC submarine cables, the capacitance of the cable acts like a long line of capacitors, drawing reactive power and causing significant voltage drops and losses over distances exceeding roughly 50–80 km. For a 190 km run, an AC system would require expensive intermediate converter stations or synchronous condensers to manage these losses. HVDC transmission eliminates the capacitive charging current issue, allowing the 500 MW of power to flow with significantly lower losses per kilometer. This efficiency makes HVDC the standard for interconnectors of this length, ensuring that the majority of the 500 MW capacity reaches the destination grid effectively.

Converter Stations at Great Island and Pembroke

The conversion between AC and DC occurs at the terminal converter stations located at Great Island in County Wexford and Pembroke in Pembrokeshire. These stations house large power electronics, typically based on Line Commutated Converters (LCC) or Voltage Source Converters (VSC), which transform the AC power from the Irish and Welsh grids into DC for transmission and back again. The Great Island station draws power from the Irish grid, converting it to ±320 kV DC, while the Pembroke station receives the DC power and converts it back to AC for distribution in Wales. These stations are critical control points, allowing for precise regulation of power flow direction and magnitude, enabling Greenlink to balance energy supplies between the two nations efficiently.

What are the key challenges in building submarine power cables?

The construction of the Greenlink interconnector presented significant engineering and logistical hurdles, primarily due to the complexity of linking two distinct national grids across the Celtic Sea. As a 190 km long high-voltage direct current (HVDC) submarine power cable, the project required precise coordination between Ireland and Wales, specifically connecting County Wexford in Ireland to Pembrokeshire in Wales. The scale of the 500 MW capacity link demanded rigorous preliminary work to ensure the stability and efficiency of the transmission line.

Marine Surveys and Licensing

A critical phase in overcoming these challenges involved extensive subsea surveys. In 2018, detailed marine surveys were conducted to map the seabed and assess environmental conditions along the cable route. These surveys were essential for determining the optimal path for the HVDC cable and identifying potential geological or ecological obstacles. The data gathered during this period informed the technical specifications and installation strategies for the project.

Simultaneously, the project faced complex regulatory requirements. Securing marine licences in both UK and Irish waters was a mandatory step to authorize the construction and operation of the interconnector. This dual-jurisdictional approval process required Greenlink Interconnector Limited to navigate distinct legal and environmental frameworks in each country. The need for harmonized marine licences ensured that the project met the operational status requirements for both nations, facilitating the seamless flow of electricity across the border.

Offshore Construction Coordination

The physical construction phase began in May 2022, marking a major milestone in the project's timeline. Offshore construction for a submarine power cable of this magnitude requires meticulous coordination among various stakeholders, including cable laying vessels, tugboats, and onshore terminal stations. The start of construction in May 2022 followed the completion of the licensing and survey phases, allowing for the systematic deployment of the HVDC cable across the 190 km route.

Coordinating these offshore operations involved managing weather conditions, marine traffic, and the precise placement of the cable to minimize tension and potential damage. The successful execution of these construction activities was crucial for the timely commissioning of the Greenlink interconnector in 2025. The project's ability to overcome these engineering and logistical challenges demonstrates the growing sophistication of cross-border energy infrastructure in Europe.

See also

• Moneypoint Power Station: Transition from Coal to Oil and Grid Stabilization
• Wind power in Ireland
• Power System Simulator for Engineering (PSS/E)
• Flywheel frequency regulation
• Availability-based tariff: pricing mechanism for Indian power grid stability

References

1. "Greenlink" on English Wikipedia
2. Greenlink Interconnector - National Grid ESO
3. Greenlink - RTE (Réseau de Transport d'Électricité)
4. Greenlink - ENTSO-E Interconnector Database
5. Greenlink - National Grid Transmission