National Grid Electricity System Operator (ESO) has predicted a tightening of capacity margins this winter due to plant closures and outages, with the gap between supply and demand expected to fall to 4.8GW during an average cold spell.

The forecast was released this morning (15 October) after the ESO issued a warning on Twitter yesterday evening that supply margins are expected to be unusually slim over the next few days as low wind output coincides with power station outages.

The body has since given updates stating that margins “remain adequate” for today.

According to the latest issue of the ESO’s annual Winter Outlook report, peak underlying demand on the electricity system is expected to fall from 60.4GW to 58GW, including 1.5GW from its operational reserve.

Generation capacity of 100.7GW of generation capacity and interconnector imports of 5GW are expected to be available to meet this demand. These suppliers have been de-rated to 62.7GW in total, giving de-rated capacity margin of 4.8GW or 8.3 per cent.

The equivalent forecast for last winter was 7.8GW or 12.9 per cent.

The margin would have been even tighter were it not for the coronavirus pandemic, which the ESO predicted would suppress peak demand by 5 per cent in its central scenario as increased consumption by households is more than offset by a drop in business usage.

The ESO said it has also explored how a further retightening of coronavirus restrictions would impact demand, with a full national lockdown expected to reduce peak demand by 11 per cent when compared to usual levels.

The forecast reduction in capacity margins is instead driven by a massive 6GW drop in nameplate generation capacity, which last year stood at 106.7GW. The ESO noted that although it has dropped since last year, the capacity margin remains higher than those forecast in 2015/16 and 2016/17.

Roisin Quinn, head of national control at the ESO, said: “Given the increased uncertainty heading into this winter as Covid-19 infections rise and negotiations continue ahead of the EU transition period ending, we want to provide assurance to industry and the public that we will be able to manage electricity supply and demand this winter.

“While we’re anticipating recently reimposed lockdown measures reducing national demand, the higher demand we tend to see over winter means we’re not expecting to see the same operability challenges we did over summer as a result.

“We await clarity around Britain’s position beyond the end of the EU transition period, but we‘ve modelled different scenarios extensively and whatever the outcome of negotiations we expect to be able to reliably manage electricity flow to and from the continent without interruption.

“We’re working hand in hand with industry to manage the network against these two major challenges and look forward to delivering secure and efficient electricity to everyone who needs it throughout this winter.”