ASA Lay Language Papers
161st Acoustical Society of America Meeting

Wind Turbine Noise - Clues to the Mystery of Why People are Hurting

William K.G. (Bill) Palmer
trileaem@bmts.com
TRI-LEA-EM  RR 5
Paisley, ON N0G 2N0 Canada

Popular version of paper - 3aNSa2
Presented Wednesday Morning May 25, 2011
161st ASA Meeting, Seattle Wash

The look in their eyes haunted me. Many people have talked to me, face-to-face, and although using different words, said the same thing, "I just cannot stand it anymore, since the wind turbines started operating near my home. Can't you do something, please?" Their eyes told the same story, of hurting, that was not being addressed. There seemed to be little that I could directly do to alleviate the situation. Perhaps, though, I might help those who could take corrective action to understand what might be causing the hurting. As a general rule, when a problem previously undetected occurs, a good place to look for clues is by examining changes. It is well known that wind turbines produce a characteristic sound. Could adding this sound contribute to the hurting? This article documents the investigation.

The project collected digitized audio sound samples at a number of locations, both at "approved locations" (as approved by regulators) as meeting their acceptable criteria, and at "control locations" at distances roughly twice and ten times the minimum approved distances from wind turbines. All test locations are located within about a 10 km (6 mile) radius of a central point, and all are subject to very similar environment, of topography and vegetation. Over 250 test samples have been collected on over 30 occasions, with each sample series collected within a 2 hour period so that weather conditions, wind speeds, and adjacent wind turbines output remained fairly constant. The same calibrated recording equipment was used to collect the data to ensure consistency. A frequency spectrum for each sample was created, separating the sound into its components to help understand its effect.

The collected data reveal:

1. When all the wind turbines are shut down, differences between the sounds at all test sites can barely be detected, other than for easily explained differences such as sea gulls flying overhead, intermittent road traffic, or insects, each of which have a distinct frequency trace. This shows that the background sound levels at all the test sites are very similar, both at the "approved locations" and the "control locations". (See Figure 1 - Sound Levels with all Turbines Shutdown)
2. When wind turbines start up, even when at very low power, all low frequency sound levels increase significantly at the "approved locations" compared to the "control locations". (See Figure 2 - Sound Levels at Very Low Power - 0%)
3. As the wind turbines output goes to about 25% of the turbine output, the additional noise changes are small at either the "approved locations" or the "control locations" compared to the very low power condition, showing that the noise changes are not primarily due to the wind speed, but due to the changes in turbine operation.
4. When the ground level wind speed increases to a "fresh breeze" that puts small trees swaying, then the sound level at the remote "control location" increased some, but still the low frequency component there was not as high as the sound level at the "approved location" when the wind turbines were at a very low power. Meanwhile the sound level at the "approved locations" increased even more. (See Figure 3 - Sound Levels at 88%)

Analysis of the sound samples also shows that the change is not just an increase in sound level at low frequency. The sound at the "approved locations" shows a very clear cyclical pattern, and periodically the sound pattern shifts to produce an even more pronounced pounding effect.

The changes that are detected do indeed give a clue of significant changes that are occurring at "approved locations" compared to the "control location" as wind turbines come into operation and increase to high power output. Some have suggested that low frequency sound level changes might have health implications, and thus the data suggests that an urgent in-depth analysis of the changes is needed to prevent more hurting, and to address the hurting that is already occurring.

Fig. 1 - Sound Levels with all Turbines Shutdown

Fig. 2 - Sound Levels at Very Low Power - 0%

Fig. 3 - Sound Levels at 88%