(Bloomberg) --

The UK exported more electricity than it imported in the second quarter of the year for the first time in more than a decade, helping make up a shortfall in France where extended nuclear outages are pushing up prices.

The volume both of electricity and gas leaving the UK jumped nearly 600% in the three months to June this year compared to the previous year, according to UK government data. Britain became a net exporter of power after generation rose by 8.2% at the same time as domestic demand fell by 5.5%, the data show. The last time the balance tipped was in 2010.

The UK has increasingly been needed to provide power to countries like France, where Electricite de France SA’s fleet of 56 nuclear reactors is running at less than half capacity due to a litany of outages and maintenance needs. French prices are among the highest in Europe and power flows along huge cables to wherever costs are highest. 

As winter approaches, it’s unclear whether such high volumes of exports can be sustained. There’s likely to be rising demand within the UK as it gets dark and cold, meaning some flows out of the country may have to be curtailed when supplies get tight. 

There may be 10 hours when power supplies are insufficient to meet demand this winter and the grid operator could need to shut off some users, according to a study by consultants Lane Clark & Peacock. Limited power imports from France and Norway through sub-sea interconnectors could compound Britain’s squeeze.

“Unfortunately, we can’t both take power from each other in the winter,” said Phil Hewitt, director at energy consultancy EnAppSys Ltd, referring to the links between the UK and France. “There is a contradiction, so there will be closed interconnectors.”

That could leave neighboring countries searching for imports from elsewhere or being forced to cut back demand at short notice. The French government has said it expects to ask households and businesses to reduce consumption over winter to avoid rolling power cuts.

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