Many people seem to be referring to the efficiency of wind turbines. From my point of view what’s important is the fact that their maximum output is always referred to, rather than their actual average output. Their actual average output is only about 25% of their maximum output; so quoting their maximum output makes them appear four times more useful than they really are. If one really wants to refer to their efficiency, one would have to compare their output with all the wind energy passing through the envelope of their blade rotation, and the figure would undoubtedly be minuscule.The wind industry would have us believe that their wind turbines are very quiet. However nothing could be further from the truth. When asked, the wind industry would probably quote a rise in noise level of about 5 decibels (dB). Of course they forget to mention that a rise of 5dB means that the noise level will have increased by a factor of about three.
Unfortunately that is only the tip of the iceberg. They will be quoting noise levels assessed using a specification called ETSU-R-97. This document was produced under the auspices of the Department for Trade and Industry (DTI). The DTI provided the chairman, and there were also 12 ordinary committee members. Of the 12 ordinary committee members, seven were employed in the wind industry.
Given the make up of the committee it is not surprising that ETSU-R-97 has been written to make the noise given off by wind turbines appear as small as possible. The figures provided under ETSU-R-97 gives no guide at all to residents in the locality as to how noisy the turbines will actually be when erected.
There are many faults in ETSU-R-97, but the main one is this: ETSU-R-97 says that the noise shall be measured using the ‘A’ weighted scale. The ‘A’ weighted scale gives such a low rating to low frequency noise, that it might as well be said that it does not measure it at all. Of course, if they were measuring the noise of a diesel engine, which does not produce low frequency noise, this would be fine. However, much of the noise produced by wind turbines is low frequency.
The wind turbine manufacturers seem unable to do anything about the devastating thump which occurs each time one of the blades comes past the main supporting tower, and of course this thump is low frequency, and so is virtually ignored by ETSU-R-97.
Professor Peter Stiles of Keel University has completed tests in relation to a windfarm at Dunbar in Scotland, and has found that infrasound vibrations are detected 10km (6.2 miles) from the site of 60m turbines as soon as they start to generate. If the turbine has three blades (as is usual) and it turns at 20 revs per minute, then there will be one thump every second, just imagine living with that! Even worse, imagine nine turbines all thumping away at once, as proposed for Batsworthy Cross. Even the wind industry itself is starting to admit that the ‘thumping’ noise is a problem.
Professor John Ffowcs Williams, a world acoustic expert at Cambridge University says modern very tall turbines do cause problems and guidelines fail adequately to protect the public.
Nicol Stephen the Deputy First Minister for Scotland, when standing beneath a newly commissioned turbine recently, said: “It was as noisy as being below the path of a very low flying aircraft.”
Such a statement is highly significant when made by the Deputy First Minister who is a vigorous supporter of wind turbine energy.
Of course low flying aircraft move on, unfortunately wind turbines do not.
W R A ALLEN,
East Knowstone,
South Molton
5 April 2007
URL to article: https://www.wind-watch.org/news/2007/04/06/thumping-home-the-real-facts/