Underground, submarine and superconducting cables: Unit economics
Why burying a line costs four to five times more
What this tab covers What it costs to move a unit of energy this way: capital and operating costs, tariffs, utilisation and how it compares with the alternatives.Over its life a buried 400 kV AC cable costs about 4.5 times as much per unit of capacity and distance as an overhead line, and a subsea DC link about five times. Spread over a well-used link, that is roughly £15 to £30 per MWh per 1,000 km (calculated).
Key costs
| Measure | Value | Note |
|---|---|---|
| 400 kV overhead line (baseline) | about 1,190 GBP per MW-km, lifetime1 | IET 2025, GB costs |
| 400 kV underground AC cable | about 5,330 GBP per MW-km, lifetime1 | about 4.5 times overhead |
| Subsea DC point-to-point link (2,000 MW) | about 6,170 GBP per MW-km, lifetime1 | about 5 times overhead |
| Long onshore DC underground cable (700 km, 2,000 MW) | about 2,270 GBP per MW-km, lifetime2 | converter cost spread over a long distance |
| Viking Link build cost | about 1,590 GBP per MW-km45 | calculated: £1.7 billion / (1,400 MW x 765 km), construction only |
| Example 15 km, 5,000 MW route | overhead about 90; buried cable about 400; new tunnel about 1,060 GBP million2 | lifetime cost, two 2,500 MW circuits (IET 2025) |
| Cost per MWh moved, underground AC cable | about 15 at full use, about 30 at 50% use GBP per MWh per 1,000 km12 | calculated, undiscounted: £5,330 over 40 years divided by 8,760 MWh per MW per year |
| Asset life | 40 years or more (IET); about 60 years (National Grid, GB underground cable) years23 | sources use different planning assumptions |
Where the money goes
| Item | Share or amount |
|---|---|
| Cable contracts within SuedLink | more than EUR 1.8 billion (2020 awards) of an estimated EUR 10 billion project (2025 estimate), roughly 18% (calculated)161722 |
| Converter stations | Large fixed cost per link, which is why long DC routes are cheaper per MW-km (about £2,270 for 700 km onshore against £6,170 for a subsea link)2 |
| Fault repair and lost output (offshore wind export cable) | About US$10 million to 30 million per incident6 |
Cables are used where overhead lines are not possible (at sea) or not acceptable (cities, protected landscapes). Their high per-km cost is therefore usually a small part of a consumer's bill, because they cover short sections or links that are heavily used. The alternative ways of moving the same energy, an overhead line or shipping fuel to generate locally, are cheaper per MW-km where feasible, but the comparison depends on route length, utilisation and permitting delay.
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
- Undergrounding high voltage electricity transmission lines: the technical issues (Issue 4) National Grid, 2015
- 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
- 80% of insurance claims in offshore wind are related to subsea cable failures DNV, 2024
- 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
- Prysmian completes perfect hat trick with SuedLink Corridor in Germany Prysmian Group, 2020