Demand is forecast to continue to be low this summer, although some resurgence is expected in comparison to levels seen in 2020.
This is according to National Grid ESO’s Summer Outlook, an annual summary of the level of demand and the challenges that arise from this in balancing the system over the summer period.
The weather corrected minimum transmission system demand is expected to be 17.2GW and occur overnight rather than in the afternoon when embedded solar output is highest. Daytime minimum is expected to be 20.1GW while the high summer peak is expected to be 32GW, with the ESO stating that it expects COVID-19 to continue to impact demand patterns with minimum demands “to be low again in 2021”.
However, this is an increase on 2020’s demand, with summer minimum coming in at 16.2GW, daytime minimum 17.6GW and high summer peak 31.5GW. It therefore puts summer 2021 levels closer to those seen in 2019, where minimum demand was 17.5GW and high summer peak 32.9GW.
The impact of COVID-19 could vary demand with both a high-impact sensitivity and a low-impact sensitivity also modelled. In the former, the UK re-enters a lockdown with similar effects to the one which began after Christmas, with transmission system demand falling as low as 14.7GW. In the latter, demand returns to the level predicted in the pre-COVID-19 period after 21 June, with the maximum credible transmission system demand being 41.7GW, although the ESO said it believes this to be unlikely.
It outlined how in spring and summer 2020, lower demand was sometimes seen during the afternoon rather than in the traditionally lowest demand periods overnight in the early hours of the morning, with the largest difference being 1.7GW on 19 April when daytime demand fell to 17.2GW compared to 18.9GW overnight.
Under normal weather conditions the ESO is not forecasting any periods where this will occur over summer 2021, although there are periods when minimum daytime and overnight demands are expected to be close. In particular, it identified the weekend of 29-30 May as being forecast to be “challenging” with daytime minimum demand only 1.6GW higher than overnight on the 29 and morning peak demand being 4.4GW higher than overnight on the 30.
However, the ESO said that throughout the summer the necessary tools will be in place to enable safe, reliable and efficient system operation. It added that based on current data, it expects to be managing periods where inflexible generation output plus flexible wind output exceeds minimum demand and to take actions to manage this including requesting pumped storage units to increase demand, curtailing wind and trading to reduce levels of interconnector imports.
Whilst it has retained its Optional Downward Flexibility Management service – introduced last summer to help manage periods of low demand – it doesn’t anticipate any requirement to use the service in its central case. Depending on weather conditions or COVID-19 impacts on demand, however, it could still be called into use, although only in the event it would prevent the need for emergency disconnections.
Within the Summer Outlook, the ESO also explained how the introduction of Dynamic Containment as well as further progress on its Accelerated Loss of Mains Change Program have reduced the impact of frequency risks being managed on the system, with the control room now being required to take fewer actions to increase system inertia.
National Grid ESO executive director, Fintan Slye, said that the two measures as well as the somewhat higher demand than in 2020 "makes us confident of being able to operate the system safely and securely, and with increased efficiency too."
He added that the "right tools and processes are in place to operate the electricity system this summer".
A record-breaking year for demand in 2020
In National Grid ESO’s 2020 Summer Outlook, it predicted that demand could fall as much as 20% as a result of the COVID-19 pandemic. The year was indeed one in which demand reached record-low levels, with national demand - how much generation must be supplied through the transmission network to meet customer demand within GB - hitting a record low of 13.4GW on 28 June 2020 when background demands were low and suppression was between 10% and 15%.
For this year, because industry and businesses have adapted to work within lockdown restrictions, the ESO doesn’t expect to see more demand suppression than the current level of 5-7% even if re-entering another lockdown.
When it comes to transmission demand, the lowest level it reached in 2020 was on 31 May when it hit 16.6GW at 15:00. Meanwhile, the lowest overnight transmission demand occurred on 10 May when it hit 16.9GW.