The National Grid ESO’s ‘Pathway to 2030, Holistic Network Design’, launched in 2022, sets out a blueprint for the electricity transmission network infrastructure required to connect very large amounts of offshore wind, helping to achieve the UK and Scottish government’s 2030 offshore wind targets of 50 GW and 11 GW, respectively.

For the north of Scotland, this will entail very significant investment in electricity transmission infrastructure, including the following:

  • two 2 GW subsea high-voltage direct current (HVDC) links from Peterhead to England: Eastern Green Link 2 (EGL2), connecting to Drax for 2029; and EGL4 connecting to South Humber. Both links will be taken forward as joint ventures with National Grid Electricity Transmission (NGET);
  • a 2 GW subsea HVDC link from Spittal in Caithness, connecting to Peterhead;
  • a 1.8 GW subsea HVDC link from the Western Isles, connecting to the north of Scotland mainland;
  • 400 kV onshore reinforcements: between Beauly, Blackhillock, New Deer and Peterhead; between Beauly, Loch Buidhe and Spittal; and between Kintore, Tealing and Westfield; and
  • an upgrade of the existing Beauly to Denny line to enable 400 kV operation on both circuits.

“Alongside and co-ordinated” with these ‘Pathway to 2030’ investments, a new HVDC switching station at Peterhead, ‘Project Aquila’, is being developed by SSEN Transmission to accelerate the development of offshore wind.

By integrating HVDC systems through multi-terminal and multi-vendor interoperability (for the first time outside China), this will help reduce the number of HVDC converter stations required for HVDC links, reducing costs and minimising community and environmental impacts.

Project Aquila is one of the UK government’s four successful first tranche ‘pathfinder’ projects being progressed under the BEIS-led Offshore Transmission Network Review Early Opportunities workstream. The other three confirmed pathfinder projects are: Equinor’s proposal for shared transmission infrastructure between the Sheringham Shoal and Dudgeon extensions projects in East Anglia; Orsted’s proposal for Gigastack, a hydrogen electrolyser utilising power from the existing Hornsea 2 offshore wind farm in Yorkshire; and Orsted’s Boudicca proposal, to co-locate a 200 MW onshore battery to the grid connection of the Hornsea 3 offshore wind farm in East Anglia.

A spokesperson for SSEN Transmission said that Project Aquila also “forms part of the scope for Ofgem’s accelerating onshore electricity transmission investment framework, with Ofgem expected to make a decision before the end of the year on which projects are to be taken forward through this new regulatory framework.”

The Peterhead site, where the planned Aquila HVDC switching station would be sited, is the location of the 1180 MW Peterhead power station. It first became operational in 1982 and in the 2000s underwent a major repowering project to convert it into an efficient and flexible gas-fuelled combined cycle power station. Further redevelopment opportunities, for a decarbonised power station at Peterhead (Peterhead Carbon Capture, or Peterhead 2), are currently being explored.

Europe’s first multi-terminal (but not multi-vendor) HVDC installation, the Shetland (Kergord)-Caithness (Spittal)-Moray (Blackhillock) link, employing Hitachi Energy’s HVDC Light technology, is already under construction in Scotland, due for completion in 2024.

This article first appeared in Modern Power Systems magazine.