Several nuclear reactors are out of action for repair but demand for electricity this winter is expected to be suppressed by lockdown © AFP/Getty Images

National Grid has warned for the second time in three weeks that supplies of electricity in Britain are going to be stretched as fewer-than-expected power generators will be available at peak times, while it is also forecasting low output from renewable sources such as wind.

The company issued a notice to the market late on Tuesday asking for more capacity to be made available the following day to increase the buffer between supply and demand, although it insisted there would still be “enough generation to meet demand”.

The group, which is in charge of Britain’s electricity system, had earlier issued a tweet warning that it was forecasting tight margins on Wednesday “owing to a number of factors including low renewable output and the availability of generators over periods of the day with higher demand”.

It is the second time in just under three weeks that National Grid has taken the unusual step of warning on tight supplies: the previous occasion was in mid-October, when a number of power generators including gas, coal and biomass plants became partially or wholly unavailable because of unexpected failures at the same time as wind speeds were low.

Blackouts are uncommon in Britain, although the growth of intermittent renewables such as wind and solar and the phase-out of polluting coal plants has presented National Grid with fresh challenges in balancing the system.

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Supporters of conventional technologies such as nuclear argue that Britain will still need to invest in more stable sources of supply to ensure the lights stay on as renewables’ share of generation grows. 

The company also in September issued a more severe notice to the market that is automatically triggered when the cushion between supply and demand falls below a certain point, although it was later retracted.

Tom Edwards, an analyst at the energy consultancy Cornwall Insight, said the latest issue seemed to be caused by lower-than-expected imports via interconnectors — subsea cables that are used to trade electricity with countries including France, Ireland, the Netherlands and Belgium.

National Grid said in a report last month that the margin between supply and demand this winter was expected to be lower than last year because of some power station outages and closures, although it still expected to remain well within the reliability standards prescribed by government.

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Several nuclear reactors have been out of action this year as they undergo repairs, including at Dungeness in Kent, although demand for electricity over the winter is expected to be suppressed by lockdown measures.

The coronavirus crisis has also provided a significant challenge to National Grid in trying to balance the system. During the first lockdown, it had to tackle strong supplies of renewable electricity at the same time as demand reached record lows.

Energy industry experts are hoping that the UK government will in a long-awaited white paper shortly shed light on how it expects to decarbonise the power sector further while ensuring there is sufficient supply.

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