UK Electricity Interconnectors: Capacity and Pipeline

Great Britain is an island, but its electricity system is not isolated. A set of high-voltage cables under the sea and across the Irish border let it buy power from its neighbours when they are cheaper, and sell to them when they are not.

This page is the official NESO register of the connection contracts behind those links: what is built, what is contracted but not yet built, and how much each can carry in each direction.

What an interconnector actually is

An interconnector is a direct-current cable joining two alternating- current grids, with a converter station at each end. That design is the point rather than an engineering curiosity: two systems run by different operators cannot be wired together directly and stay stable, but converting to DC and back lets them exchange power while each keeps control of its own frequency.

It also means the flow is dispatched rather than emergent. Somebody decides how much to send and which way, usually through a market that settles the price on each side. Power moves toward the more expensive market, which is why the direction can reverse within a day.

The contract register

NESO publishes the contracted connection capability for each link. The figures below are that register, grouped by project status and by the transmission owner whose network the link connects into.

One caution about the status table before you read it: a staged project can appear under more than one status at once, so the counts are not additive. That is a property of how connection contracts are written, not a fault in the data.

Import and export are not the same number

The register quotes capability in each direction separately, and the two often differ for the same link.

Both are stated from the Great Britain grid’s point of view. Import capacity is what the link can feed into the GB transmission system; export capacity is what the GB system can supply to the link’s connection site. The asymmetry usually comes from the local network rather than the cable — the substation, the surrounding circuits and what else is connected nearby all constrain how much can be absorbed or supplied at that point.

Neither figure is a flow. Nothing on this page tells you what any link is doing at the moment, only what it is contracted to be able to do. For actual metered flow, that is on the live electricity page.

Why interconnectors matter to your bill

Wholesale electricity in Britain is priced by the most expensive plant needed to meet demand. Usually that is a gas station, so the gas price ends up setting the electricity price for everyone.

An interconnector adds a competitor to that final slot. If power can be bought from a neighbour for less than the marginal gas plant would charge, it displaces the gas plant and the price settles lower — for every unit sold in that period, not only the imported ones. That is the main route by which cross-border capacity reaches a household bill, though it arrives diluted and delayed: on a capped or fixed tariff, wholesale movements take months to show up, if they show up at all. The price cap page sets out how much of a bill is wholesale cost in the first place.

There is a security argument too. More links mean more independent sources of supply on a tight evening, which is worth something even in the hours when the price effect is small.

Contracted is not built

The register includes projects at every stage, from operating links to proposals that have a connection agreement and nothing else.

Subsea cables are among the slowest infrastructure there is: seabed surveys, consents on both sides of a border, cable manufacturing slots booked years ahead, converter stations at each landing point. Projects that hold a contract for years without moving are normal, and some are abandoned. Read the status column before treating anything here as future capacity, and read the grid connection queue alongside it for the same distinction applied to generation.

Is imported electricity clean?

It depends which link, and when. Electrons carry no label, so an import is best understood as a share of whatever the neighbouring system was generating at that moment rather than as output from a particular plant.

That makes the answer specific to each connection. A link to a hydro-dominated system delivers something close to that system’s mix; a link to a nuclear-heavy one, that mix; a link to a system burning coal or gas at the time, that. Great Britain’s published grid carbon intensity does account for imports, which is why the live figures move when a large link changes direction.

It is also why claims that Britain has “offshored its emissions” through interconnectors need checking against the direction of flow. The cables run both ways, and in windy conditions Britain is frequently the exporter.