A lack of wind in the UK this month has caused many of the country's wind turbines to slow down.

Wind energy output across the UK is down 40% from the same time last year, according to a study at Imperial College London.

This is despite the fact that more turbines have been built in the interim.

Dr Robert Gross looked at data for the Wales, England and Scotland, and found that wind turbines have generated around 2-3 gigawatts.

During a windier period, generation can be as much as 9-10 gigawatts.

Last month, turbines produced less than 2% of Britain's electricity - the lowest output in two years.

Dr Gross said that due to the the fact that Wales is on the west coast, it is better positioned to benefit from wind coming in from the Atlantic Sea.

Pen Y Cymoedd, in Treorchy, is the largest onshore wind farm in Wales.

Run by Vattenfall, the 76 turbines generate enough energy to power nearly 200,000 homes every year.

Site manager, Pat Delaney, said: "The first quarter of this year saw record high wind speeds on site which has been followed by a less windy second quarter, but certainly not a wind drought.

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"With wind, solar and battery technology all part of our low carbon energy project portfolio in the UK, the fluctuations we’ve seen are expected and planned for as we develop the future energy mix needed for a climate smarter future.”

National Grid confirmed that on average, around 15% of Britain's electricity comes from wind power, but data starting from July 1 this year put the monthly average closer to 6.9%.

An unusually long period of high pressure is to blame for the lack of wind. With the jet stream located much further north, the area of dense high pressure air over the UK hasn't moved.

A National Grid spokesman said: "Between 4th June and 15th July wind generation was around 30% lower compared to the same period last year. Electricity demand is low and we’re comfortable with the level of spare generation we have available."