Wind farms produce far less energy than previously claimed, according to a new report.
Wind-energy output at wind farms metered by the national grid was less than 10% capacity for one third of the time during the two-year study.
Low output also sometimes coincided with periods of peak demand.
The report, supported by Scottish conservation charity the John Muir Trust, said wind “cannot be relied upon” to provide any significant level of energy generation at any defined time in the future.
It cited an “urgent need” to re-evaluate the implications of a reliance on wind for any significant proportion of Scotland’s energy requirement.
The study found that for numerous extended periods of time all the wind turbines linked to the National Grid muster less than 20MW of energy: enough power for 6,667 households to boil their kettles for a cup of tea.
It also called into question common assertions made by industry such as that wind turbines will generate on average 30% of their rated capacity over a year.
It found that average output from wind was just 24.08% between November 2008 and December 2010.
Stuart Young, author of the report, said: “Over the two-year period studied in this report, the metered wind farms in the UK consistently generated far less energy than wind proponents claim is typical.
“The intermittent nature of wind also gives rise to low wind coinciding with high energy demand. Sadly, wind power is not what it’s cracked up to be and cannot contribute greatly to energy security in the UK.
“It was a surprise to find out just how disappointingly wind turbines perform in a supposedly wind-ridden country like Scotland. Based on the data, for one third of the time wind output is less than 10% of capacity, compared to the 30% that is commonly claimed.”
The study analysed electricity generation from all UK wind farms which are metered by National Grid between November 2008 and December 2010.
All were in Scotland until three in England were added to the study in July 2010.
The study challenged assertions by industry and government such as that periods of widespread low wind are “infrequent”.
It found that the average frequency and duration of a low wind event of 20MW or fewer was once every 6.38 days for a period of 4.93 hours.
The study also found that at each of the four highest peak demands of 2010 wind output was low, being respectively 4.72%, 5.51%, 2.59% and 2.51% of capacity.
Wind generation was below 20% of capacity for more than half the period of the study.
The report also suggested that pumped storage hydro was not the solution to low periods of wind output.
It said that if all four UK pumped storage plants were to be run simultaneously at full capacity, the stored water would be exhausted in around 24 hours
Helen McDade, head of policy at the John Muir Trust, the UK’s leading wild land conservation charity, said: “This report is a real eye-opener for anyone who’s been wondering just how much power Scotland is getting from the fleet of wind turbines that have taken over many of our most beautiful mountains and hillsides.
“The answer appears to be not enough, and much less than is routinely claimed.”
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