Any extension of the below-normal wind farm output seen so far this year could trigger a steep rise in gas use by UK power firms heading into winter, with tighter gas supplies and higher gas prices a likely outcome.

A strong late-year rebound in UK wind power output, however, could lead to reduced domestic gas use by UK power firms, and potentially higher gas and power exports by the UK during Europe's key gas consumption period over the winter.

SUB-PAR 2025 FOR WIND... SO FAR

Monthly UK wind electricity generation fell below the year-before output total during six of the first eight months of 2025, data from Ember shows.

Total wind electricity output so far this year was just over 48 terawatt hours (TWh), which was 8.3% or 4.3 TWh less than during the same months in 2024.

The wind output total for the January through August stretch was the lowest for that period since 2022, and resulted in wind farms accounting for the lowest share of the UK's electricity generation mix since 2022.

Wind farms generated 31.9% of the UK's utility-scale electricity supplies during January to August, compared to close to 35% for the same months in 2024.

GAS OFFSET

To offset the dip in output from UK wind farms, UK power firms dialled up gas-fired power generation by 17.5% from the same months last year, and to the highest in two years.

The closure of the UK's last remaining coal-fired power plant last September also helped boost gas-fired generation this year, and also led to the highest power generation total on record from the UK's diesel-fired power stations.

Gas-fired power accounted for 33% of UK utility electricity generation, which is up from a 29% share during the same period in 2024.

Going forward, gas will remain the UK power sector's main source of dispatchable power, especially during periods when intermittent output from wind farms falls short of expectations.

Gas will also be the power sector's main heating source during upcoming cold spells in the UK, where temperatures are forecast to trend lower going forward but should hold above the long-term average for the coming month, data from LSEG shows.

SEASONAL UPSWINGS

Both wind and gas generation tend to see upswings heading into the latter months of the year.

Wind electricity production in particular has historically seen a sharp upturn during the final quarter of the year compared to the July to September quarter, as wind speeds at turbine level pick up with the change of season.

Between 2019 and 2024, wind electricity generation in the UK during the final three months of the year jumped by an average of 65% compared to the average generation during the July to September quarter, Ember data shows.

Wind power's share of the UK generation mix also historically increases notably as the year progresses, from an average of around 30% a month during the middle of the year to closer to 40% during the peak winter months.

UK power generation from fossil fuel power plants also historically rises from mid-year into winter.

Between 2019 and 2024, total fossil fuel electricity generation during the last three months of the year averaged around 18% more than the output levels during July to September, due to higher demand for heating in winter.

Historically, both coal-fired and gas-fired power plants were cranked up to generate that higher power supply, but with the UK's coal plants now closed gas plants will do most of the wintertime heavy lifting going forward.

TIGHT STOCKS

A key constraint on UK gas generation potential during the coming winter will be the volume of gas supplies on hand during any sudden cold snaps which trigger a demand surge.

Historically, the UK has relied mainly on its pipeline network from its own production fields and from exporter nations for its gas supplies, and so does not tend to maintain a large volume of inventories in domestic storage tanks.

However, given the lack of back-up coal plants since late 2024, the UK power system is expected to increase the overall volume of gas it consumes during peak demand periods.

That in turn is expected to put its existing supply networks under strain during any unexpected bouts of higher gas use, and lead to more regular drawdowns on existing stockpiles.

Stock drawdowns have already been evident so far this year, with average inventories from January 1 through September 15 41% less than during the same period in 2024, and the lowest since 2021.

Gas traders have historically used the months of September and October to rebuild stockpiles ahead of the winter rush, and so still have time to stock up this year.

And power firms can traditionally rely on greater power supplies from wind farms to meet much of any additional load requirements during cold and breezy days.

But with UK wind output still consistently holding below year-earlier levels, some power suppliers may start to worry that wind output may remain stunted for the rest of 2025, and that higher gas generation will be needed to balance system needs.

For gas traders, that in turn could trigger consistently above-normal gas demand through the end of the year, as well as periods of sharply higher gas demand whenever power demand spikes during cold snaps.

Just how big the swings in gas use will be closely linked to wind farm output, which gas traders will need to watch more closely than ever during the coming autumn and winter.

The opinions expressed here are those of the author, a columnist for Reuters.

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