Down to the electric wire

02/04/2024

Tom Harris examines the supply chain constraints facing the growing number of interconnector projects As 2024 began, Britain’s latest high-voltage direct current (HVDC) interconnector was switched on by National Grid. A record-breaking 760km long, Viking Link connects the Bicker Fen substation in Lincolnshire with the Revsing substation in Southern Jutland, Denmark. The project is the sixth of its type for National Grid, raising its operational portfolio to 7.8GW (gigawatts) of the UK’s now 9.8GW of interconnector capacity. While Viking Link broke records with the length of its onshore and subsea transmission span, it is only the first of a further 16GW of interconnector connection capacity in the pipeline for completion by 2035. Since Britain became a net exporter of electricity for the first time in 44 years in 2022, National Grid has projected net power exports to increase to 64TWh (terawatt-hours) in 2030, and up to 104TWh by 2050. Watts the demand? Interconnectors are high-voltage cables linking the grids of countries, regions and/or offshore assets, enabling electricity to be transmitted between them. They use HVDC technology rather than the more commonly used high-voltage alternating current (HVAC), which is used across Britain’s overhead line pylon network. Although its components are more expensive, HVDC is highly efficient for conducting electricity over long distances, particularly underground or underwater. Electrical losses from DC transmission range between 2 and 3% in comparison with 5-10% by AC. Break-even distances to financially justify HVDC installation in terms of the cost benefit from reduced energy loss compared with an HVAC alternative are 50-95km for underground cables, and 24-50km for submarine cables, far smaller than the 600-800km required to break even when constructing HVDC overhead lines. However, HVDC transmission does require expensive converter stations at either end of a transmission span to switch electricity supply back to the conventional AC format. As more countries seek to decarbonise their energy systems, there is a higher reliance on weather-dependent renewable energy generation to meet supply. Interconnectors allow for the importation of renewable energy from unaffected areas while managing the precise amount of power imported to aid grid stabilisation and management. A tangled supply chain Growth in HVDC interconnectors has put significant strain on the supply chains required to construct the cabling and the converter stations needed at each end of a transmission line. The European market for HVDC cabling and converter stations is dominated by a small pool of suppliers, because of the complexity of manufacturing parts and the high barriers to entry. Converter stations are typically provided by Siemens, GE Grid Solutions or ABB, while cabling is contracted to either ABB, Prysmian PowerLink, Nexans or NKT. On top of the backlog of component orders, the availability of specialist subsea cable installation vessels and support ships is also limited. The combination of these capacity constraints risks an increase to cable delivery lead times and programme costs for interconnectors in the pipeline and those requiring maintenance. This is all while the EU has set a minimum interconnection target of 15% by 2030. National Grid has previously suggested the need to broaden the supply chain beyond traditional European manufacturers – its 720km North Sea Link interconnector was built by Japanese supplier Hitachi Energy. The developer, which is also behind the proposed 3,800km Xlinks interconnector linking Morocco to the UK, aims to construct purpose-built cable factories to meet the volume of cable required. If the benefits of interconnectors to energy security and decarbonisation through the facilitation of renewable generation are to be realised, the HVDC supply chain must adapt or face ever-increasing costs and delay to programmes. Tom Harris is a graduate EIA infrastructure consultant at Temple Group