"What you can't hear, can hurt you"
The Shirley wind project low frequency sound study was requested by, and partly sponsored by, the Wisconsin Public Service Commission.
The purpose was to determine whether infrasound was present in the homes of three families in the footprint of the Shirley Wind project owned by Duke Energy. These families have reported adverse health effects since the wind turbine utility commenced operation. All three have been forced out of their homes. They report experiencing symptoms of the type associated with wind turbine syndrome. These families offered to act as intervener's in another Wisconsin case, Highland Wind, which is in the application hearing phase. Fifty affidavits were filed representing 50 residents near the utility, describing adverse health effects and home abandonment for the eight turbine Shirley Wind project (click here for video) using Nordex N100 2.5 MW wind turbines.
Three homes were studied. R1 is about 3500 feet from the nearest wind turbine. R2 is about 1100 feet, and R3 is about 7000 feet away. All three homes were found to have measurable infra and low frequency sound from the wind turbines, with levels decreasing as distance increases. The peak acoustic energy was found at the wind turbine's blade passage frequency, which is less than 1 Hz for the Shirley Wind wind turbines.
Most modern upwind industrial scale wind turbines, including the 1.5 MW turbines commonly installed over the past 5 years, can operate with hub rotation speeds that are similar to those of the Nordex. As turbine sizes (blade length, tower height, and in general power output) increase, the more likely it is that the hub rpm will be in the range similar to that of the Nordex units.
Rob Rand, one of the participating acousticians, has a chart in the Team Report that shows the range of rpm's against the frequency associated with inducing nausea that shows this trend. This is an important chart for showing how the conclusions for this PSC study of a single wind utility has implications for other wind utilities using other makes and models of wind turbines.
Initially the PSC was going to have the study conducted by George and David Hessler. This posed a problem for credibility with the interveners and others who know their position from other projects. The attorneys for the citizen's group, Anne Bensky and Peter McKeever for Forest Voice, and Glenn Reynolds, the attorney for the Town of Forest which also opposes the project, wanted the tests to be conducted but were concerned that the Hesslers would produce a biased study. It was decided they would push for a study that included four acoustics experts, some on the wind industry side (Hesslers), independents (Schomer and Walker) and one who has demonstrated the ability to find infrasound inside homes (Rob Rand).
The purpose of the study was to collect high quality audio samples during periods when the family members were present and "feeling" the wind turbines. Wind speed and direction data at the outdoor microphones and from the wind turbine hub level anemometer was also collected. Wind turbine power production was also collected. (The data from wind turbines is under a protective order and only available to select reviewers.) The Team Report summarizes the data and protocol. It also includes a Team conclusion and separate appendices from each acoustician providing additional information about what they observed or derived from the study. They can also file follow-up reports as can other qualified experts within the time frame for responses to the PSC.
Mr. Walker's equipment was the best of any of the acousticians, and became the focus for data collection. Unlike the instruments traditionally used by acousticians studying wind turbine infrasound, Mr. Walker's equipment could accurately measure sounds in the lower region of infrasound. It allowed synchronized sampling and recording at multiple sites inside and outside a home over the frequency range from 0.5 Hz to 100Hz. These audio samples have been made available to Wade Bray and me for analysis using Head Acoustics' software in a similar manner to what was done for the Bray/James study and Noise-Con 2011 paper on the GE 1.5 MW turbine in Ubly, MI.
Although there are details in the report that I would take issue with, I can say that the Team portion of the report presents a major step forward in the discussion about why adverse health effects are being reported by people living near modern industrial scale upwind wind turbines. The primary conclusion of the TEAM is:
The four investigating firms are of the opinion that enough evidence and hypotheses have been given herein to classify LFN and infrasound as a serious issue, possibly affecting the future of the industry. It should be addressed beyond the present practice of showing that wind turbine levels are magnitudes below the threshold of hearing at low frequencies.
The argument about whether wind turbines produce infra and low frequency sound and, if they do, is it sufficient to cause adverse health effects, has taken a big step forward with this conclusion. That infra and low frequency sound is a primary characteristic of wind turbine acoustic emissions was established by the team. The argument that infrasound produced by modern upwind wind turbines does not have sufficient amplitude to reach the threshold of hearing (set for steady pure tones, not the complex mix of tones emitted by wind turbines) raised by the wind industry through its experts like Dr. Leventhall and the many acousticians and others who parrot his opinion, is now discredited.
I think this is a major step forward. We still need to establish what levels and other characteristics of infra and low frequency sound are needed to produce adverse health effects, but the argument that it is not present is shown to be false. The wind industry and its supporters can no longer say that wind turbines do not produce significant levels of infra and low frequency sound just because the sound pressure levels do not rise to the Thresholds of Perception of audible sounds.
Thus, "What you can't hear, can hurt you" is the surviving paradigm.