AGL’s Head of Wind Energy Compares Wind Turbine Low Frequency Sound to the Beach

Waubra Foundation Chairman to Mr Trompf, February 12, 2014

Dear Mr Trompf,  

Reading your email of February 4 to Mrs Gardner is a reminder of a Dutch Admiral Van Trompf de Ruyter, mostly abbreviated to Admiral Trompf, who tied a broom to the top of his mast to signify his scorn of the Royal Navy and his mastery of the English Channel. A year passed and the Royal Navy destroyed the power of the Dutch fleet and in a triumphal gesture the English Admiral mounted a whip on his flagship. 

Apparently Trompf was not familiar enough with the latest technical information that he should have known about. Such ignorance ultimately proved fateful for the Dutch Navy. 

Perhaps it is not just chance, but from reading your letters to Mrs Gardner you clearly do not understand the technology of noise from turbines and, seemingly, not very much about noise at all. Lack of knowledge is merely unfortunate, but using ignorance of the physics of noise to rebut easily verified claims by Mrs Gardner may, in the end, become quite fateful for the Macarthur Wind Project and the people involved. You doubtless know the saying “if you ignore history you are bound to repeat it.” 

Normally I would correspond with AGL’s Chairman, but I was so appalled by your letter to Mrs Gardner, whom you address as Ann, that I felt compelled to give you some technical advice from an engineer who has studied the noise from turbines matter for seven or more years. 

So let me tell you, in the clearest way I can, the stone cold, irrefutable facts about wind turbines with some particular references to Macarthur. 

Neither AGL nor the Victorian DPCD knew what they were doing (and let’s hope that they really did not know) when they worked together to increase the size of the already approved turbines for Macarthur. Neither apparently knew that larger turbines emit a significantly larger proportion of noise as infrasound thus increasing the proportion of the most dangerous sound frequencies emanating from the turbines. With the increase in turbine size, removing some turbines to keep the total power output of the project constant did not keep the noise the same. Also the larger turbines needed a new noise assessment and a consequent new layout. You may be able to prove that was addressed, but no one has ever seen such evidence. 

Now to basics: 

  • · Wind turbines produce sound across a range of frequencies including infrasound (0 to 20 hertz) and low frequency sound (generally said to be below 200 hertz), together known as ILFN. Sound at 100 hertz is audible at around 27dB for an average group of people whilst the level of sound required for average audibility rises quite quickly below, say, 25 hertz. So at infrasound frequencies the air pressure pulses (otherwise known as noise) exist and are detected but often in a different way to audible noise above 20Hz.
  • · Infrasound is indeed common in our world, but most natural infrasounds are irregular and random or are transient events (e.g. earthquakes). Some frequency bands below 20 hertz have been shown to annoy and cause harm to humans at well below audible levels. Industrial anthropogenic sounds are often regular and repetitive, as is the case with wind farm noise emissions, across the audible and infrasonic spectrum.
  • · Infrasound travels much larger distances than audible noise and easily penetrates normal building materials and can resonate building elements (i.e., increase in impact), inside rooms. Most audible sound propagates with a noise reduction of 6 dB per doubling of distance. Infrasound is different and attenuates at only 3 dB per doubling of distance for a small number of turbines (say, two). However, infrasound attenuation has been found to be minimal for the Macarthur wind farm out to distances beyond 5 km simply due to the large area covered by the wind farm.
  • · Some frequency bands of infrasound are relatively harmless and indeed even pleasant to the body, including waves on a beach. Organ music at frequencies just below 20 Hz generate ‘feelings’ in people that can be either pleasant or unpleasant and have been designed to produce emotive effects. Once it is understood that different frequencies can have very different affects on humans it is easy to realise how foolish and unscientific was the study that exposed two groups of NZ students to 10 minutes of infrasound at 5 hertz.

    Noise that is ongoing and can be present at any time causes the damage to humans to intensify with exposure; and even if neighbours escape from their “sick” house for a period, the health problems return when they come home; in other words the accumulated damage and the sensitisation starts again where it left off. People do not acclimatise to infrasound, they become more and more damaged with ongoing exposure.
  • · Many otherwise respectable (“OWR’) acoustic firms know the truth about wind turbines, and have known that from studies done in the USA in the 1980’s. The lead scientist of those studies recently told the Australian Newspaper that the conclusions then were equally relevant to modern turbine designs.
  • · OWR firms helped form the NZ Noise Standards for wind projects and “helped” ignorant planning authorities in Australia shape the guidelines for wind projects. History has shown that these guidelines were designed to encourage development, not to put in place guidelines to ensure no harm to nearby residents was caused. In fact these guidelines have turned out to be licences to damage, as much as to build and operate. You will of course realise that the law of nuisance overrides planning guidelines and, ultimately, the money will be found to prove a case of noise nuisance in the courts and the game, as it is now played, will be over.
  • · One of the more active developers surprisingly inferred that he knew there was (or at least could be) a health problem by saying at a NSW meeting, words to the effect that: if we meet the guidelines then, if there is a problem, it is due to the standards being at fault, and that is the government’s problem; however if we do not meet the standards then it is our fault and our problem. Even a modern day Dutch Admiral could agree to that.
  • · Now we return to the OWR acoustic firms. It will be proven that their methodology (and instrumentation) is not thorough or careful enough to properly define compliance. As you know, some projects still remain non-compliant after years. The Clean Energy Regulator has been rumbled on this matter and it is unlikely that it will again give yet unproven projects an automatic approval for compliance and hence RECs as before. It is also highly likely that rechecking compliant projects will show a number to be not compliant, some will be so bad that they will never be compliant and maybe forced to shut down, at least at night. Noise measurements by independent acousticians have already indicated that Macarthur will have trouble proving real compliance.
  • · Of course we have to face the unavoidable fact that a compliant project may still, and in fact is likely to, cause damage to neighbours for two reasons: the standard only refers to dBA and thereby omits reference to ILFN ; and even with regard to audible noise it refers to a minimum of 40 dBA whereas every other form of industrial or other noise in country and city is limited to 35 dBA maximum. There is no technical basis for such an aberration. Perhaps this was gift by Labor governments to developers. 

Clearly there is a gap between yourself and the most senior AGL management, and presumably between that management and the moral code of AGL as set and overseen by the Board. You possibly feel a little isolated and without the tools or the authority to fix the real and ongoing noise and consequent health problems. Presuming this is so, this letter will be published on our website as will other letters to AGL’s Chairman. 

Our advice to you and indeed to AGL is: stop trying to talk the noise problem down and quoting rubbish studies; take the lead and show a really responsible attitude to amelioration of the problem with an open, thoughtful, totally science-driven inquiry by one or more independent acousticians (we can suggest a few that are independent, competent and in possession of the necessary instrumentation); investigate all frequencies of noise at distances inside and outside houses at up to 12km from the nearest turbine. Finally consider the impact of the noise on project neighbours; this will need help from pyscho-acousticians and again we can lead you to people with these skills. 

In the meantime get into the practice of shutting down turbines at night so that your neighbours can cease suffering from sleep deprivation. 

You might also note that it is now possible to retrofit noise measurement and control systems inside “sick” houses on existing projects. Ultimately these will become compulsory; take the lead, not fright. 

Yours faithfully,
Peter R. Mitchell, AM, BchE.

Download the email exchange between Mrs Gardner & Mr Trompf→
Download Mr Mitchell’s letter to Mr Trompf→