One of the major obstacles faced by acoustic experts when trying to do meaningful wind turbine ‘noise’ testing is the dogged refusal of wind farm operators to provide wind speed and operational data.
Moreover, wind power outfits have resisted, with granite-like tenacity, quite reasonable calls by noise experts to shut down their turbines (ie “on-off testing”) during the process; a step that would show – unequivocally – what noise is attributable to the turbines’ operation (as complained of by victims) and what might be put down to “wind in the trees”, the source wind industry spin-masters routinely scape-goat as the reason for the neighbours’ complaints.
STT champion, Mary Morris changed all that when she provoked the South Australian Environmental Protection Agency (EPA) to conduct on-off testing at the Waterloo wind farm in SA’s mid-north.
Mary’s efforts set up a unique opportunity, which attracted several of Australia’s top research acousticians to the neighbouring farm houses – in the hope of finally getting a meaningful data set, with the turbines shut-off for periods long enough to separate out turbine noise from the rest. Those that lined up at Waterloo included top-flight noise and vibration experts, like Professor Colin Hansen (see our posts here and here).
However, the operator – Energy Australia – fighting all the way – ‘offered’ to do no more than shut down its turbines for trifling intervals of 40-50 minutes – and to do so at times when complaints don’t normally occur (ie during the day-time and early evening, rather than after 10pm when people are out for a little ‘shut-eye’). Hmmm…
But – to the noise experts’ delight – where decent and reasonable corporate conduct failed them – mechanical serendipity intervened: a cable fault in the line that feeds power from the wind farm to the substation nearby saw the whole operation shut down for 54 hours straight. The ‘lucky’ break occurred at a time when the independent noise experts had the surrounding homes bristling with state-of-the-art kit.
The results gathered, didn’t disappoint: a top-team from Adelaide University, headed up by Professor Colin Hansen, were able to separate out the ‘environmental’ noise (wind in the trees, etc) from the low-frequency noise generated by turbines at distances out to 8.7km.
The length of the unscheduled shut down allowed the team (Kristy Hansen, Branko Zajamšek, and Professor Colin Hansen) to identify the turbine noise ‘signature’ within and external to three neighbouring homes.
Their results were presented at the Internoise Conference (43rd International Congress on Noise Control Engineering November 16-19, 2014 in Melbourne, Australia) in a paper titled “Comparison of the noise levels measured in the vicinity of a wind farm for shutdown and operational conditions” – which can be accessed here as a PDF.
The team – using narrow band spectra analysis – were easily able to contrast ‘environmental’ noise from the turbine ‘signature’ – as depicted in the graphs below: the blue lines showing noise levels with the turbines off; and the red lines showing noise levels with the turbines on (to enlarge it, click on the graph, it will pop up in a new window and you can use your magnifier from there).
So far, so obvious.
When even Blind Freddy can spot the difference, it’s little wonder that wind power outfits have fought tooth-and-nail to avoid meaningful on-off noise testing.
Thanks to their ‘lucky’ break, the researchers conclusions in their paper were:
There is a significant difference in the unweighted third-octave spectra when the Waterloo wind farm is shut down compared to when it is operational for each of the three residences investigated in this study.
The most prominent difference occurs in the 50 Hz third-octave band and it has been shown that operational levels can be as much as 30 dB higher than shutdown levels.
The peak in this third-octave band is also higher than the audibility threshold defined in ISO 389-7 (12) by as much as 10 dB for the outdoor measurements.
This peak was also measured indoors when the wind farm was operational but the magnitude is slightly lower and the rms level averaged over 10 minutes is at the same level as the audibility threshold defined in ISO 389-7 (12), although the variability in the noise results in the peak levels being much higher than the rms audibility threshold.
Outdoor infrasonic noise levels associated with wind farm operation vary depending on the local wind speed at the microphone. During periods of negligible wind at the microphone, distinct peaks corresponding to blade-pass harmonic frequencies are clearly distinguishable.
The outdoor results presented for House 3, where the wind speed at the microphone was zero, showed the most distinct peaks in the infrasonic frequency range out of the three residences investigated. For Houses 1 and 2, these peaks in the outdoor spectra were evidently masked by wind-induced noise and this is further confirmed by their presence in the indoor spectra for measurements at these locations, as shown in Section 3.1.1 and 3.1.2.
The wind-induced noise is caused by pressure fluctuations and vortex shedding, which are sensed by the microphone but bear no relation to acoustic disturbances. Therefore, to adequately portray the levels of infrasound outdoors, it is imperative that there is negligible wind in the vicinity of the microphone.
The shutdown times selected by the wind farm operator gave few opportunities to record such conditions. Hence, it is suggested that in future studies, times between 12 am and 5 am with negligible wind at the measurement locations are selected for shutdown/operational comparisons.
The narrow-band spectra associated with wind farm operation show a consistent occurrence of peaks at specific frequencies in the infrasonic and low frequency ranges.
The frequencies of these peaks are the same at each residence and they are not present when the wind farm is shut down, which indicates that they are the result of wind farm noise.
The low frequency peaks at 23.3 Hz, 28 Hz, 46.6 Hz and 56 Hz are surrounded by side-bands spaced at the blade-pass frequency of 0.8 Hz. Results obtained by increasing the frequency resolution indicate that it is quite feasible that the low frequency peaks are harmonics of the blade-pass frequency.
Thus their presence can either be attributed to selected amplification of blade-pass frequency harmonics or amplitude modulation of a turbine associated noise source at the blade-pass frequency. Further investigation into the source of the noise is currently being undertaken.
Kristy Hansen, Branko Zajamšek, and Professor Hansen (2014)
Nice work team!
But results like that shouldn’t require ‘lucky’ breaks and serendipitous shut-downs. Meaningful, independent wind turbine noise testing should be available to neighbouring victims, as a matter of course.
The terms and times at which turbines should be shut down for that purpose should be a matter for the experts engaged – not the wind industry, its parasites or the pet acoustic consultants that it employs to fluff and obfuscate on its behalf (the ones that wrote the noise standards for the wind industry on a ‘made-to-not-measure’ and ‘avoid-scrutiny-at-all-costs’ basis and – who, for no other reason than benefiting their wind industry paymasters, upped the noise limits from 35dB(A) to 40dB(A) – as Mary Morris points out in her brilliant letter to the EPA).
No, ‘luck’ should only be a matter of concern to horse punters and cardsharks, not independent acoustic experts trying to help wind farm victims get control of a noise source that destroys their ability to sleep, and otherwise drives them mad in their homes; if it hasn’t already driven their owners out of them.
Fortunately, it’s wind industry shenanigans – like that outlined above (that requires good fortune – rather than common sense and science to get to the proper result) that is squarely in the sights of the Senate Select Committee, its terms of reference including the following:
(1) That a select committee, to be known as the Select Committee on Wind Turbines be established to inquire into and report on the application of regulatory governance and economic impact of wind turbines by 24 June 2015, with particular reference to:
(d) the implementation of planning processes in relation to wind farms, including the level of information available to prospective wind farm hosts;
(e) the adequacy of monitoring and compliance governance of wind farms;
(f) the application and integrity of national wind farm guidelines;
For those suffering from or threatened by turbine generated low-frequency noise and infrasound, now is you chance to hammer the so-called ‘standards’ and planning ‘controls’ that mean proper noise testing is a matter of ‘luck’ and not good measure.
Why not drop a submission to the Senate Inquiry along those lines? Note that the opportunity to make submissions to the Committee ends on 27 February 2015. See the link here.