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Wind Turbine Noise Testing A Fiasco

Fri, 08 Oct 2004

Wind Turbine Noise Testing A Fiasco

The absurd conclusions drawn from a recent test programme to ascertain the noise levels of Windflow's experimental turbine at Gebbies Pass near Christchurch shows the dubious processes by which these projects are pushed through.

Following two weeks of testing during which the turbine was switched off several times during reasonable wind conditions depsite assurances that it would be run "continuously" whenever there was adequate wind, the results obtained by the Banks Peninsula District Council's testing officer David Shovel were "peer reviewed' by Marshall Day (their letter of 7 October attached). This contains so many oviously illogical statements that it undermines the credibility of the entire process.

Marshall Day's analysis begins to look suspect when in point 4 they concede that the indication that sound levels are lower when the turbine is operating "cannot be the case". The next point that "the turbine is not contributing to the measured sound levels at this location" (local resident Julie Riley's property) may have some abstract theoretical interest but is utterly absurd in practice since it implies that all the people who have recently heard the turbine VERY clearly over background noise are imagining they can hear it! Point 5 contradicts Point 4 by asserting that the sound is "slightly higher" with the turbine on at 5.5m/s windspeed than with it off; then states "this is possibly a quirk in the regression system" and continues, "it is possible to theoretically correct the 'turbine on' measurement.....". It continues

"SUCH A PROCESS IS NOT PARTICULARLY RELIABLE...." (my emphasis) but proceeds to cite calculations purportedly showing that at 5.5m/so the turbine is producing no more than 26dBA. Even leaving aside the obvious point that this is only one specific windspeed, one has to question the theory as opposed to what happens in practice. And as the owner of an Oxford maths degree I must challenge the reasoning of anyone drawing definite conclusions from a process they admit to be inaccurate! Marshall Day then cite the (previously unheard of) Malcolm Young Associates test sound levels at an unspecified site from which they calculate sound levels of "about 20 dBA" at Julie Riley's property. The sound heard at different locations - even within one property - varies greatly so unless they tested on Ms Riley's, property, what possible basis can they have for making such a statement? Surely if Marshall Day's analysis is valid they would not be scratching around for supposed verification from such vague "evidence".

Point 7 states "It is not possible to accurately determine the sound level at higher wind speeds" (presumably 5.5m/s - the lowest speed at which the turbine operates and the only wind speed figure cited). Nevertheless Marshall Day then give their "opinion that sound from the turbine is almost certainly less than 30 dBA at Ms Riley's property under

ALL (my capitals)operational wind speeds", a statement which clearly discredits the whole testing process. Is this science - or a huge guessing game? While it is widely claimed (including by Windflow's ceo) that sound levels are measurable here we have a crucial test totally discredited by the admission that it is not possible to measure accurately and that sound levels can only be judged by the "opinion" of the person analysing the data. If Stuart Camp of Marshall Day had spent time on Ms Riley's property during the tests he would realise his theories and opinions are meaningless in practical terms.

Having previously admitted it is not possible to determine the turbine sound levels at higher wind speeds, point 8 recommends further testing "particularly at wind speeds above 8 m/s". What is the point of this? Then it says that this shall be carried out "45m from the base of the turbine in the direction of Ms Riley's, property", suggesting that Marshall Day do not even understand that location is crucial to the sound levels actually heard. Marshall Day then say this information should "be used to predict noise levels at the Riley property". So test results for wind speeds over 8m/s under a process which is admitted cannot be accurate are to be used to predict noise levels at the Riley property about a kilometre away from the testing site?? This clearly defies all logic.

Marshall Day's graph appears to show the turbine putting out between 30dBA and 46 dBA. Since none of their report of 7 October explains how they transform this data to their "opinion " regarding very low sound levels at Ms Riley's property, and since their conclusions bear little resemblance to the turbine sound levels actually heard in parts of McQueen's Valley including Ms Riley's property, Marshall Day's 7 October letter is a totally unconvincing account of how they reached their conclusions.

To summarise, what this whole process has done is that having led to the admission that it cannot be accurate, it then proposes further tests well away from the property under discussion involved to "predict" sound levels at that property while also clearly implying that the many people who find the noise levels objectionable on and around Julie Riley's priority are imagining things.

With other windpower advocates claiming that their turbines are silent (Windflow stated that their turbine would be heard for not more than 5 percent of the time it is running) the Gebbies Pass tests again demonstrate the flaws in their arguements. Given that the conclusions drawn from the sound tests are as illogical as shown by Marshall Day's analysis of 7 Oct. there is obviously a pressing need for a truly independent enquiry into the Gebbies Pass turbine and whole issue of the noise problem created by wind turbines wherever they are proposed.


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