Off-shore wind turbines take power from the National Grid when not generating electricity, it has emerged.
They use electricity to keep their blades rotating slowly in cold weather to prevent them icing up and to power the systems which turn the blades into the wind.
It costs around twice as much to produce electricity using offshore wind than at traditional coal and gas-fired power stations.
Critics say it is a ‘folly’ that turbines need National Grid power even when idle. But experts counter by saying that all methods of producing power need to use electricity to function.
The issue has flared up after one resident in North Wales told how he had observed more than 100 turbines off the coast ‘idling very slowly’ in freezing conditions.
Brian Christley, of Conwy, raised his concerns in a letter to The Daily Telegraph. He wrote: ‘Over the weekend just gone – the coldest of the year so far – all 100-plus offshore wind turbines along the North Wales coast were idling very slowly, all using grid power for de-icing and to power their hydraulic systems that keep the blades facing in the same direction.’
RWE, the energy company which owns 30 turbines off North Wales, said its machines in the area contributed power to the National Grid on both days.
A spokesman said: ‘Our turbines were not idling but generating electricity during each of the days in question, contributing a positive balance of energy into the grid.
‘All energy generators use a small amount of electricity to keep their systems running smoothly, in the case of wind farms drawing power from either an adjacent operating turbine or the grid. These quantities are tiny compared to what is returned to the network.’
Turbines can operate with wind at speeds of 10mph to 50mph after which they shut down.
They produce electricity 70 to 85 per cent of the time, depending on their location. Around 10 per cent of electricity generated in the UK comes from wind power.
RenewableUK, the wind industry trade association, said wind farms need a ‘tiny fraction’ of the power they generate to run.
‘The best comparison is to think of how much electricity you would use to boil a kettle compared to how much an entire village would need to power everything,’ a spokesman added.
‘All generators, including gas and nuclear plants, use some electricity as well as producing it.’
In September, it was revealed that the amount of electricity generated by wind farms had dropped by 20 per cent, despite 900 turbines being built in 2013.
Britain’s offshore and land wind turbines have a total capacity of 12.1 gigawatts, enough to power 8.8million homes. But output was cut by ‘very low wind speeds’ in the three months to last June, said the Department of Energy and Climate Change.
Critics said the industry will always be vulnerable to the whims of the weather despite huge investment to meet EU targets.
The Tories have said they will cap the number of onshore turbines if they win May’s election.
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