What Is an Interconnector, and Why Are Countries Building More of Them?

The basic idea

An interconnector is a transmission link — usually a subsea or underground HVDC cable — that connects two separate national power grids, letting electricity flow between them. The UK alone has interconnectors to France, the Netherlands, Belgium, Norway, and Denmark, with more under construction.

Why it's worth the enormous cost

Electricity prices vary constantly between countries based on local generation mix, weather, and demand. An interconnector lets a country import cheaper power when its neighbor has a surplus (windy day in Denmark, say) and export surplus power the other direction when roles reverse — smoothing out price volatility and reducing the amount of expensive backup generation or storage either country needs to build purely for its own emergencies.

Why renewables specifically make this more valuable

Wind and solar output varies by weather system, and weather systems don't respect borders — but they also aren't perfectly correlated across a few hundred kilometers. A calm day in one country can coincide with a windy day in a neighboring one. Interconnectors let a renewable-heavy grid lean on a neighbor's surplus instead of firing up a fossil backup plant, which is a big part of why interconnector buildout has accelerated alongside renewable buildout, not independently of it.

The engineering reason it's HVDC, not HVAC

Long subsea cables use direct current (HVDC) rather than alternating current, because an AC cable of that length generates enormous reactive power losses from the cable's own capacitance — a problem that gets worse, not better, with distance. HVDC avoids that loss mechanism entirely, at the cost of needing expensive converter stations at each end to transform AC (from each country's domestic grid) to DC for the crossing and back to AC on arrival.

The takeaway

An interconnector is really a long-distance arbitrage and resilience tool as much as it's a piece of infrastructure — it turns weather differences between neighboring countries into a shared asset instead of two separate problems, which is exactly why Europe keeps building more of them as renewable penetration rises.