SCOTLAND'S wind farms have produced only around half the amount of power they were expected to this year, Scotland on Sunday has learned. The government blamed the low generation levels on unusually calm weather, but critics said the figures showed the danger of becoming too dependent on renewable energy.
Turbines are expected to operate at an average output of about 30 per cent of their maximum installed capacity.
But the average output over five months this year was 17 per cent – just over half the expected average.
There have been long spells when virtually no electricity has been produced by any of the country's wind farms.
Helen McDade, head of policy at the John Muir Trust, which campaigns to protect wildlands in Scotland, said: "This raises serious concerns about security of supply. We have always been told that even if it isn't windy in one part of the country, it will be elsewhere. However, this suggests that is not the case.
"What will the consequences be when we become more reliant on wind power, and switch off the other resources, such as the coal-fired power stations?
"I think vested interests and blind hope are the reasons we are careering down this route."
Stuart Young, who runs Caithness Wind Information Forum and opposes wind farms, carried out the research by analysing data from the Balancing Mechanism Reporting System website, which the National Grid uses to monitor generation. The site provides a constant flow of information on output from 1,588 megawatts wind farms in Scotland.
His research also showed that for 80 per cent of the time between February and June Scotland's turbines were operating at less than 30 per cent.
And for almost a third of the time they were operating at less than 5 per cent of their maximum output, meaning they were virtually becalmed.
Only nine times between February and June had the wind farms achieved 30 per cent efficiency for a full day at a time. There were long stretches, such as from 16 to 29 May, 9 to 15 April and 6 to 23 February when they failed to reach 30 per cent output.
Young said: "At the moment there's not a big enough penetration of wind to cause National Grid a problem, but the more we rely on it and the less we use fossil fuels the more likely there is to be a set of circumstances when – with very high demand and very low output – the only thing is to turn customers off.
"I hope this makes the politicians sit up and listen. They are not listening now. They have got their hands over their ears and they are in thrall to the wind industry."
However, Rosie Vetter, policy manager for onshore wind at Scottish Renewables, said "cherry picking" data over such a short period was "totally meaningless" because trends have to be looked at over a longer time frame.
"The most recent annual figures show over a fifth of Scotland's electricity demand was met from renewables," she said. "No single energy technology can meet all of our needs, which is why we need a mix of renewables and thermal generation in different locations linked by a strong grid, with enhanced capacity to store electricity so it can be released when it is needed."
Dr Richard Dixon, director of WWF Scotland, also said he was not worried by the figures. "It was a quite unusual period weather-wise so it's not a great surprise that in that period they weren't producing what we would normally expect."
He said Denmark gets 20 per cent of its electricity from wind farms, and does not have difficulty maintaining supply.
He said creating more ways to store electricity from renewables would help provide back-up during "extremely rare" situations when supply was so low. "It's not a trivial problem, but it's also not a hugely difficult problem," he said. "And if we need to have a gas-fired power station sitting there that may need to be switched on for five days a year then that wouldn't be a terrible thing."
Duncan McLaren, chief executive of Friends of the Earth Scotland, said: "We understand that 2010 has been an unusually calm year, but in the face of the uncertainties of the detailed local impacts of climate change on future Scottish weather we need to ensure we have a robust and secure electricity generating system." A spokeswoman for the UK Government's Department of Energy and Climate Change said: "Wind speeds have been lower than the nine-year average in each of the first five months of this year, so this will have affected the generating output of wind farms."
However, she added: "Generally, the wind is blowing somewhere in the UK and the likelihood of low wind speeds affecting 50 per cent of the country occurs less than 100 hours per year."