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Wednesday, 4 July, 2001, 18:38 GMT 19:38 UK
Flying bugs get the chop
Wind turbine, PA
Whirling turbines can behave oddly at high speeds
Aerodynamics specialists are used to dealing with tricky questions like how a bee flies when it apparently should not.


It really is a serious problem in some parts of the world

Gustave Corten
ECN
And now they have solved a 15-year mystery of why wind turbines often perform poorly in high winds, when they would be expected to give a high output.

"It is a really serious problem in some parts of the world - California, Gibraltar and the Golan Heights," Gustave Corten of the Energy Research Centre of the Netherlands told BBC News Online.

"We were working up to 20 hours a day, coming up with new theories every day and then having to discard them," he added.

Flying menace

The culprit turned out to be an unexpected one: flying insects.

"It has been known for a hundred years that contamination affects aerodynamics but we didn't believe it was insects," he said.

If insects were responsible for the problem then Gustave Corten and his colleague Herman Veldkamp of Danish wind turbine maker NEG Micon would have expected the performance of the turbine to get steadily worse as the squashed insects built up on the blades.

Instead, the output of the turbine decreased in series of clear steps. And in any case, insects tend not to fly in high winds.

"They can't fly in high winds because they can't control where they are going. They need high humidity to stop them drying out, relatively high temperatures and gentle winds.

"Some insects like flying ants only fly one or two days a year," he explained.

Observations

After weeks in California observing turbines with reflecting indicators illustrating the flow of air around the blades, the researchers realised what was going on.

First of all, dead insects were accumulating on the blades during good flying conditions, but because the wind was so low, the insect build up was having no effect on performance.

But then, when the wind picked up, the solid mass of insect bodies stuck fast to the blades and caused the characteristic stepped drop in output from the turbines.

Sadly, no high-tech solution is in sight. "You just have to clean the blades. After a while, the insects dry out and turn into such a rigid object that you have to use a screwdriver to get them off," he said.

A wet turn in the weather is the best hope. "If it rains, we advise turbine operators to start their machines and get them cleaned for free," he added.

The research is published in the scientific journal Nature.

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See also:

02 Jul 01 | Sci/Tech
Europe discusses wind power
18 Jun 01 | Scotland
Turbines bring wind of change
05 Apr 01 | UK Politics
UK to get 18 wind farms
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