Underground, submarine and superconducting cables: Technology advances
525 kV plastic cables, offshore grids and superconducting tape
What this tab covers The newest technologies in service or close to adoption, what each improves, and how the main options compare.Cables are moving to higher DC voltages and bigger ratings per circuit, offshore links are starting to join into networks, and superconducting cables are moving from short demonstrations to the first multi-kilometre city links. In 2025-2026 the binding limit is factory and ship capacity more than technology.
Latest advances
525 kV XLPE DC cable being deployed · 2025Extruded plastic-insulated DC cable at 525 kV; Germany's 700 km, 4 GW SuedLink uses it, with cable contracts worth more than EUR 1.8 billion awarded to NKT and Prysmian in 2020 (calculated from the two firms' announcements).2161722
Improves: About 2 GW per cable pair, roughly double a 320 kV pair, so fewer trenches per GW.
Long land-and-sea interconnectors in service · 2023Point-to-point DC links over hundreds of km, such as Viking Link (765 km).45
Improves: Joins national markets so surplus wind or hydro can be shared.
Multi-terminal offshore DC grids demonstration · 2025DC networks joining several offshore wind hubs and countries instead of single links.12
Improves: Fewer landfalls and shared capacity; the IET describes the technology as new.
High-temperature superconducting cables demonstration · 2021-2026Ceramic-tape conductors cooled by liquid nitrogen; Shenzhen 10 kV, 400 m demonstration (energised 2021) and Munich's planned 15 km, 110 kV SuperLink, whose test system NKT powered up in 2024.89
Improves: Very high power in a narrow duct with no ground warming or external magnetic field.
Bigger HVDC cable factories and ships being deployed · 2025LS Cable and System completed a fifth subsea cable plant at Donghae, South Korea, in July 2025, which it describes as Asia's largest HVDC cable factory and says raises its HVDC subsea output more than fourfold; affiliate LS Marine Solution is building a 10,000 tonne laying ship.2127
Improves: Eases the multi-year wait for DC cable.
Comparing the options
| Option | Efficiency | Cost | Capacity or distance | Maturity |
|---|---|---|---|---|
| 400 kV overhead line (baseline)1 | Not quantified here; air cooling allows thinner conductors | About £1,190 per MW-km over life | Several GW per route; no length limit for AC | mature |
| 400 kV underground AC cable17 | Extra insulation and sheath losses plus charging current | About £5,330 per MW-km, about 4.5 times overhead | Practical up to tens of km | mature |
| Subsea DC point-to-point link (2,000 MW)127 | About 2.6 to 3.1% per 1,000 km at full load (calculated) plus about 1% per converter | About £6,170 per MW-km, about 5 times overhead | Hundreds of km | mature |
| Multi-terminal offshore DC network12 | As DC links, plus more converters | About £12,500 per MW-km, about 11 times overhead | Several hubs and countries | demonstration |
| Superconducting cable89 | No conductor loss; continuous cooling needed (about 2 W per metre heat leak at Shenzhen) | No public figure; high system cost, including HTS tape, is described as the main barrier | Hundreds of metres to about 15 km so far | demonstration |
Conventional XLPE cables, AC and DC, are mature and bankable and are being scaled up in voltage. Underground AC suits short sensitive sections; DC wins over long distances and at sea because it has no continual charging current. Multi-terminal DC grids are described by the IET as a new technology and are the most expensive per MW-km. Superconducting cables solve a different problem, fitting large power into crowded city streets, and remain at demonstration scale. Across all options the IEA reports that real cable prices have nearly doubled since 2019 and DC cable procurement now takes more than five years, so delivery slots matter as much as technical merit.
Sources
- Electricity transmission technologies: costs and characteristics (summary flyer) Institution of Engineering and Technology (IET), with Mott MacDonald, 2025
- Electricity transmission costs and characteristics: final full report IET / Mott MacDonald, 2025
- National Grid announces commercial operations of Viking Link National Grid, 2023
- Laying of world record power cable between the UK and Denmark now complete National Grid Ventures, 2023
- HVDC transmission (presentation by L. Tang, HVDC 2013) US Department of Energy, 2013
- SuperLink superconducting cable system NKT, 2025
- Development and demonstration of concentric-type HTS power cable for distribution grid in Shenzhen urban area Frontiers in Energy Efficiency, 2023
- Germany starts construction on two more stages for 4 GW SuedLink HVDC cable S&P Global Commodity Insights, 2025
- NKT awarded over EUR 1bn order for the SuedLink high voltage DC project NKT, 2020
- Construction of 'Asia's Largest HVDC Cable Facility' Wraps Up offshoreWIND.biz, 2025
- Prysmian completes perfect hat trick with SuedLink Corridor in Germany Prysmian Group, 2020
- LS C&S quadruples HVDC cable capacity through addition of cable production plant Wire Association International (WAI), 2025