Wind Turbine Noise: Real Impacts on Neighbors

“ When neighbors complain of disturbed sleep, [wind noise models] might cite a predicted level of 40 dBA, when the actual noise that triggered awakening was a 50+ dBA spike making turbine noise the problem.”

“Hessler & Associates agreed ‘that a wind turbine is indeed a unique source with ultra low frequency energy’ and that a ‘new Threshold of Perception’ was needed to assess turbine noise impacts.”

“Former Vestas’ CEO, Ditlev Engel has admitted that larger setback distances are the only way to address low frequency and infrasonic impacts, particularly on larger (3MW) turbines. Bigger setbacks means fewer locations for siting turbines near where people live.”

In late January, the Iowa Policy Project, Iowa Environmental Council, and the University of Iowa’s Environmental Health Sciences Research Center (IPP et.al.) jumped on the ‘wind energy is safe’ bandwagon with a joint release claiming wind turbine noise does not pose a risk to human health. Their conclusion was based on a summary of the ‘best’ research available to IPP et.al. but mainly relied on two papers – one by the Council of Canadian Academies (“CCA”) and a second by McCunney et.al.[1]

The Research

Briefly, CCA and McCunney et.al. reviewed relevant literature looking for causal links between exposure to wind turbine noise and negative health effects. Both concluded that individuals living in proximity to turbines experienced higher levels of annoyance but could not state with certainty whether the annoyance was attributable to turbine noise or other factors such as attitudes toward the visual appearance of the turbines or financial reward.

In other words, people who dislike the look of the turbines or who are not financially vested in the project may be more annoyed and higher levels of annoyance could cause people to notice the noise.

IPP et. al. was quick to accept, and repeat this conclusion but failed to acknowledge the obvious limitations of existing study designs – limitations that both CCA and McCunney et.al. admit.

Noise Prediction vs. Actual Measurement

One notable limitation pertained to turbine noise assessments. Most of the studies surveyed relied on standard modelling methods to predict sound levels rather than actual field measurements. This means that when individuals self-reported that their sleep was disturbed by turbine noise, the researchers calculated the noise level at the time of the disturbance and made a judgement whether turbine noise, or just general annoyance, was to blame.

Modeled turbine noise levels in this situation are inappropriate substitutes for actual noise measurements.

Since modeled turbine noise is averaged over the long-term, it excludes the unmistakable “swish-thump” characteristically heard in turbine noise emissions. This “swish-thump” is the amplitude modulation caused by the rotating blades moving through the air. Modeling also cannot account for varying atmospheric conditions at wind energy facilities (ex: temperature gradients and turbulence) that promote louder operational conditions.

CCA concedes that “…periodic amplitude modulation may be a critical component of sound from wind turbines that triggers annoyance.” And the effect is not minor. Fluctuations in actual noise levels due to amplitude modulation can vary in excess of 10 dB above predicted values while meteorological conditions can produce variations up to 14 dBA over predicted levels.

This is consistent with Ken Kaliski’s finding that an additional adjustment of 11 decibels would have to be added to modeled sound power levels in order to estimate operational peak sounds produced by the turbines. Kaliski is an acoustician and contributing author to McCunney et.al.

Prediction noise models under-predict the loudest turbine noise levels heard by neighbors at the point when their sleep is interrupted. This is a significant factor that cannot be dismissed.

When neighbors complain of disturbed sleep, researchers might cite a predicted level of 40 dBA, when the actual noise that triggered awakening was a 50+ dBA spike making turbine noise the problem.

None of this is new nor surprising. In 2012, acoustician Howard Quinn wrote that the

annoying character of wind turbine sound is primarily due to amplitude modulation, which causes the sound level to go up and down continually.… And, unlike the situation with regard to continuously occurring sound (fans, busy highways), it is very difficult to become accustomed to uneven sound. In fact, many residents have reported being more annoyed with turbine sound over time rather than less. The effect is particularly pronounced with very large turbines featuring relatively low rotation rates, where the amplitude modulation is at its greatest.

Infrasound and Low-frequency Noise

With audible turbine noise levels potentially well above those calculated by researchers, it is likely noise is reducing the quality of sleep for neighbors. But what about low-frequency and inaudible levels? CCA and McCunney et.al. dismiss low-frequency emissions claiming these levels are too far below the hearing threshold to be consequential.

This was not the finding of five acousticians including Hessler & Associates (who works almost exclusively for the wind industry). In 2012, which predates CCA and McCunney et.al., the researchers measured “unequivocally” the presence of low level infrasonic sound emissions inside a residence near the Shirley wind facility in Brown County, Wisconsin. The low-frequency noise was found to be uniform throughout all rooms and not just those facing the turbines. Long-term, the wife and child residing there reported severe health impacts and the family eventually moved away.

Hessler & Associates agreed “that a wind turbine is indeed a unique source with ultra low frequency energy” and that a “new Threshold of Perception” was needed to assess turbine noise impacts.

Steven Cooper’s work at the Cape Bridgewater wind facility in Australia found six individuals were able to “sense attributes of the wind turbine emissions without there being an audible or visual stimulus present.” More specifically, Cooper found that inaudible turbine sound emissions disturbed his study subjects even when they could not hear the turbines or see them moving. The “adverse reactions to the operations of the wind turbine(s) correlate[d] directly with the power output of the wind turbine(s) and fairly large changes in power output.”

Propaganda vs. Perception

The wind industry is heavily invested in a propaganda campaign aimed at convincing the public — and decision makers — that wind turbine noise is safe at any distance. The campaign, in part, involves blaming neighbors and their negative attitudes about turbines for their discomfort while avoiding measuring the actual “swish-thump” of the spinning blades.

Their campaign also requires dismissing low frequency noise and for good reason. Former Vestas’ CEO, Ditlev Engel has admitted that larger setback distances are the only way to address low frequency and infrasonic impacts, particularly on larger (3MW) turbines. Bigger setbacks means fewer locations for siting turbines near where people live.

Vestas and others can complain, but the damage from turbines can no longer be ignored. There are enough turbines operating worldwide, and enough people impacted, for the public to recognize turbine noise is intrusive and potentially harmful to neighbors. Trivial reports produced by agenda-driven researchers in Iowa are unlikely to divert attention away from this fact.

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[1] McCunney et.al. was fully funded through a grant of the Canadian Wind Energy Association. The authors “declare no conflicts of interest.” The paper’s primary authors, Robert J. McCunney, MD, MPH, Kenneth A. Mundt, PhD, and W. David Colby, MD each have relationships with the wind industry including, but not limited to, payments received from the wind industry to serve as experts and/or prepare reports for the wind industry that examined the potential health impacts of wind turbines.

McCunney et al. only states that “Drs McCunney, Mundt, Colby, and Dobie and Mr Kaliski have provided testimony in environmental tribunal hearings in Canada and the USA” with no further declaration as to the nature of those proceedings or their respective paying sponsors.