A £600m cable connecting the UK and Belgium’s energy systems is about to be switched on, becoming the first of a new generation of interconnectors that will deepen the UK’s ties to mainland Europe just as it prepares to leave the EU.

The Nemo link is in the final stages of testing and from early 2019 is expected to transmit power over an 80-mile route along the seabed between Richborough in Kent and Zeebrugge, becoming the first new electricity interconnector to the continent since 2011 and the first to Belgium.

Although built with the expectation of the UK mostly importing electricity, in the short-term, Nemo will provide a boost to Belgium.

Six of the country’s seven nuclear plants are offline this winter because of repairs and safety checks, raising fears of blackouts. That means UK power stations will initially be largely exporting via Nemo when it becomes fully operational in early 2019.

The business secretary, Greg Clark, lauded the project for continuing “close cooperation across borders with our European partners”.

Facebook Twitter Pinterest A DC hall in a converter station in Zeebrugge, which converts electricity between AC and DC, to send power across the Nemo link interconnector. Photograph: Pieter Clicteur/National Grid

The UK has four electricity interconnectors, one to France, one to the Netherlands, one to Ireland and one to Northern Ireland, with the French and Dutch ones largely importing power.



However, the UK’s rapidly changing energy mix, relatively high power prices and government support – which are backed in Theresa May’s Brexit deal – has set the scene for a rapid expansion in interconnectors.



“As we’re going through the energy transformation, we’ve got a lot of changes in generation. Interconnectors are increasingly important,” said John Pettigrew, the chief executive of National Grid, which has built Nemo with its Belgian counterpart Elia.

Such schemes are considered vital for managing the intermittent nature of renewables, which are growing fast.



“There are going to be periods going forward where there is surplus renewable energy, too much wind or too much solar. Therefore being able to take it from a local area and move it around Europe is good for carbon emissions,” Pettigrew said.

Interconnectors boost energy security, he said, citing the role they had played during the “beast from the east” cold snap last winter. The company calculates the cable to Belgium will save UK consumers £80m-100m a year.



Nemo is one of four links being built by National Grid, including a 720km one to tap Norway’s hydro power, and a 760km one – the world’s longest – to harness Denmark’s windfarms.



Another company is completing an extra link to France through the Channel Tunnel, expected to go into commercial operation about a year after Nemo. Other firms are eyeing cables to countries as far away as Germany.



The idea has even been mooted of bringing geothermal power from Iceland. However, Pettigrew said the distance would be a “real technical challenge” and Icelandic energy firms have told the Guardian the prospect currently looks unlikely.



The government expects imports via interconnectors to increase from 6% now to 20% by 2025. Unlike new nuclear plants such as Hinkley Point C, which is expected to take around decade to complete, they can be built relatively quickly: work started on Nemo in 2015.

The project was on time and on budget, despite encountering more than 1,000 objects on the seabed during the laying of the interconnector, including an 18th century cannon, unexploded bombs and parts of British, German and US second world war planes. “It was a difficult job offshore,” said Tim Schyvens, Nemo’s chief engineer.

This year the cable was pulled onshore in Belgium, buried beneath a beach and run a few miles underground to a station that converts electricity from direct current (DC) to alternating current (AC) so the Belgian electricity grid can use it.

Inside the station, Schyvens points out where the interconnector emerges from the ground, an unremarkable-looking 14cm-diameter black cable that can transmit enough power for a million homes.

This facility and an almost identical one in Kent together account for about half the project’s cost, and a glimpse inside the facility’s heart, the 23-metre high converter hall, give an idea why: it is filled to the rafters with thousands of transistors that convert the electricity.



Links such as this are also being driven by other countries’ energy revolutions. The French president, Emmanuel Macron, said last week that France would reduce nuclear from 75% of power supplies to 50% by 2035, by building more renewables and interconnectors.



Looming over all the UK projects is the shadow of Brexit. Pettigrew maintains the trading of electricity with EU countries will still work and consumers will see no difference in their energy bills. “In all the scenarios we are considering, including hard Brexit, there is no reason the energy can’t flow,” he said.



However, the executive did admit trading could become less efficient if the UK leaves the EU’s internal energy market as part of a no-deal Brexit, with traders potentially needing to use two systems rather than one. He said contingencies had been made for such an outcome.