“Forward wholesale electricity prices are higher than last year,” the ESO says in its annual winter outlook report published this morning.
“In addition, tight margin days are likely to see significant price spikes in the balancing mechanism.”
The country’s few remaining coal-fired power stations are also likely to run more frequently than last year, it added, due to the prices they can earn to fill in gaps in supply.
The ESO warned in July that Britain should prepare for constrained power supplies over winter, with nuclear power plants shutting down and demand bouncing back from the pandemic.
At the time, it forecast a winter margin – the difference between supply and peak demand – of 4.3GW, or 7.3pc.
In its full winter outlook published this morning, its base case is now for a margin of 3.9GW or 6.6pc – with a range of between 4.2pc and 8pc.
A key factor leading to the cut in forecast for the winter is understood to have been a fire at a converter station in Sellindge, Kent, on September 15.
The blaze knocked out the IFA interconnector bringing in about 2GW of power from France. About half of that is expected to be back online this month, but the rest not until late March 2022.
The 6.6pc forecast margin for this winter is the lowest forecast since 2016, when it was roughly the same, but higher than 2015. It remains well within the Government’s reliability standards for the system.
The ESO’s modelling is likely to be heavily scrutinised amid ongoing chaos in energy markets due to a global crunch in gas supplies.
Wholesale gas prices have risen more than six-fold on normal, leading to a more than four-fold increase in wholesale electricity prices as so much electricity is generated in gas-fired turbines.
The price cap on energy bills has already risen £139 to £1,277 and experts predict it could rise by another almost £400 in April.