UK went entire winter without calling on backup generators

The Electricity System Operator (ESO) went the entire winter without calling on backup generators to provide additional power in times of system stress.

It is the first time in four years that the ESO has gone an entire winter without issuing a system notice.

The last time the ESO went an entire winter without issuing either a capacity market notice (CMN) or an electricity margin notice (EMN) was in 2019/20.

The mechanism was put in place in 2016, with notices issued during that first winter period. No capacity notices were then issued in the following three winters (2017/18, 2018/19, and 2019/20).

However, the mechanism was called upon at least once in every winter from 2020/21 until 2022/23.

System notices are issued to maintain a large enough cushion of spare capacity to minimise the risk of blackouts. CMNs are triggered automatically, while EMNs are manually sent out to generators by operatives at the ESO.

“There was no requirement to issue system notices due to insufficient margins during the period as sufficient reserves were maintained,” the ESO’s Winter Review states.

“There were a few periods with low generator availability, mostly due to lower wind generation. However, these periods were not prolonged.

“From February onwards we saw a greater number of days where generator availability was below the forecast in the Winter Outlook Report. This was caused by unplanned, extended nuclear outages.”

The ESO’s review reports that winter margins were broadly within the expected range with no interruption to customer demand due to unavailable supply.

It states that despite two notable cold spells in November/ December and January, milder than average weather conditions across the winter meant that it was able to maintain sufficient capacity without calling on backup generators.

As previously reported by Utility Week, the review confirms that balancing costs over winter 2023/24 fell by over 40% year-on-year, principally driven by lower wholesale costs.

The review also reveals that Britain imported more electricity from Europe than the ESO had forecast.

“We expected to see periods when exports flow from Great Britain to Europe, including over some peak periods,” the review adds. “Over winter we saw Great Britain being an importer of electricity from continental Europe over peak periods on the vast majority of days.

“We did see exports to Europe over peak periods on a small number of days.”

The review explains that the UK’s position as a net importer of electricity was largely driven by low electricity prices in Europe with day-ahead peak prices in Britain generally higher than those of connected European countries.

For example, peak prices in Britain over the winter averaged at £83/MWh compared to £68 in France, £64 in Norway and £72 in Belgium

“Interconnectors continued to be mutually beneficial for Great Britain and connected countries over winter 2023/24,” the review concludes.

For next winter, the ESO is forecasting a de-rated margin of 5.6GW (9.4%), which is 1.2GW higher than the winter just gone.

The ESO’s Early View of Winter Outlook states that the year-on-year change is due to increased interconnector capacity, new gas generation, growth in battery storage capacity and the effects of increased generation connected to the distribution networks.

The Early View adds: “We expect to have sufficient operational surplus throughout winter […] even when we consider the expected natural variation of demand, wind and outages.

“As with previous winters, there may be some tight days where we need to use our standard operational tools, including the use of system notices.”

ESO chief operating officer Kayte O’Neill added: “Our initial assessment of the winter ahead indicates that we will have sufficient margins throughout the period. Factors such as increased interconnector capacity, new gas generation, growth in battery storage capacity and increased generation connected to the distribution networks are contributing to higher margins than last winter.

“Global energy markets are showing signs of stability, but uncertainties remain and therefore as a prudent system operator we remain vigilant, continuing to monitor potential risks and working closely with our partners to establish any actions necessary to build resilience.

“We are continuing to meet the challenge of reliably operating a changing electricity system as new technologies, and diverse forms of capacity, contribute to security of supply.”