Energization of Europe’s first and world’s second multi-terminal HVDC subsea link goes full steam ahead

August 29, 2024, by Melisa Čavčić

Denmark-headquartered power cable manufacturer and installation player NKT has wrapped its assignment on a 260-kilometer high-voltage direct current (HVDC) subsea link, which is envisioned to lend a helping hand in ensuring Shetland’s supply of clean, low-carbon power, enabling 600 MW of renewable generation as remote North Sea islands connect to Britain’s main grid in support of Scottish and UK net zero and energy security targets.

Once the turnkey project of connecting the Shetland Islands to the main grid in Scotland has been finalized in close collaboration with the country’s transmission system operator (TSO) SSEN Transmission, the 320 kV HVDC interconnector, known as the Shetland HVDC Link, has been fully energized, as a key contributor to the integration of renewable energy in Great Britain, according to NKT.

The Danish player, which sees interconnected power grids as essential elements of the green transition, explains that the Shetland HVDC Link allows 600 MW of renewable energy to flow from the Shetland Islands to the Scottish mainland. NKT’s work on the project entailed the installation of 253 km offshore and 10 km onshore power cables, unlocking the Islands’ renewable potential. This power cable project is said to have been completed on time, in line with budget, and with high consideration for the local environment and biodiversity.

Darren Fennell, Executive Vice President, Head of NKT’s high-voltage business in Karlskrona, Sweden, commented: “We are pleased to continue our collaboration with SSEN Transmission, utilizing our extensive HVDC technology expertise to support a low-carbon power supply for the Shetland Islands. With the completion of the Shetland HVDC Link, our contribution to the development of the power grid in Scotland and Great Britain continues.”

Since the power cables for the Shetland HVDC Link were manufactured at the NKT factory in Karlskrona, Sweden, said to run on 100% renewable electricity, this helped minimize the carbon footprint of the cable system. The company began work on a new cable extrusion tower at the facility in July 2024. The installation of the submarine power cable system was completed by NKT Victoria, which the Danish firm describes as one of the most energy-efficient cable-laying vessels in the industry.

“During the project, we took extra precautions to monitor and protect the local wildlife. This proves it’s possible to enable the green transition while safeguarding local wildlife during cable installation,” added Fennell.

Based on SSEN Transmission’s data, around 500,000 homes and businesses can be powered by homegrown clean energy from Shetland, following the completion of two major clean energy projects on the islands, which entail the energization of the 260 km subsea link to transport electricity between Shetland and the GB mainland, and construction of SSE Renewables’ Viking Wind Farm.

Huw Jones, Executive Director at BAM Nuttall, noted: “Not only have we contributed to a project which connects Shetland to the National Grid for the first time, we’ve also taken another step towards securing a greener, fossil fuel free future for the United Kingdom. We’re still at the early stages of that journey, but the entire team who have contributed towards delivering our work in Kergord can be incredibly proud of their achievements.”

The archipelago’s first link to the GB electricity grid resulted in investment amounting to £125 million (close to $165.2 million) in the Shetland supply chain. The MET Office claims that the Shetland Islands region is the windiest area of the UK, with an average annual wind speed of 14.6 knots. As a result, the Shetland projects alone are anticipated to produce enough clean energy to power hundreds of thousands of homes, with Viking expected to be Britain’s most productive onshore wind farm per annual electricity output.

Niklas Persson, Managing Director of Hitachi Energy’s Business Unit Grid Integration, remarked: “We’re proud of this landmark achievement for the UK and to collaborate once again with SSEN Transmission. As we collaborate to advance a sustainable energy future for all, we continue to set the benchmark for deploying innovative solutions at scale. Multi-terminal solutions are important building blocks for realizing the climate-neutral grid..”

Furthermore, the HVDC cable runs from a new converter station at Kergord in Shetland to a new switching station at Noss Head on the Scottish mainland, near Wick in Caithness. NKT deems this project “world-leading as a multi-terminal HVDC link – the first in Europe and only the second in the world (the other being in China),” opening the flow of energy to be split in different directions, in this instance being sent from the switching station to both the HVDC converter stations at Spittal in Caithness and Blackhillock in Moray.

The CLV NKT Victoria installed the subsea cable in three campaigns throughout 2022 and 2023, with the final section installed on the seabed last autumn. The final energization was completed in August 2024, connecting Shetland to the GB electricity transmission system. The work continues to connect Shetland’s existing electricity distribution network to the transmission network, linking Shetland’s homes and businesses to the GB grid for the first time via the new grid supply point constructed at Gremista.

The Kergord-Gremista 132 kV overhead lines and underground cable circuits, which are currently being installed, are scheduled for completion by the end of 2025. Afterward, they will connect the HVDC link to the new Gremista grid supply point.

Rob McDonald, Managing Director of SSEN Transmission, underlined: “The Shetland HVDC Link project is a hugely important investment in the journey of Shetland, Scotland and the UK as a whole towards a clean energy future – linking Shetland to the GB electricity grid for the first time. We can all take huge pride in the fact that it has been delivered ahead of time, on budget, and above all safely.

“It is a truly world-leading project here in the north of Scotland, as the very first multi-terminal HVDC link in Europe, and only the second on the planet. Delivering a project of this size and scale sets a new standard for what we can achieve. It has required innovation, collaboration, and resilience – qualities that will be crucial as we press forward with our Pathway to 2030 investment programme.”