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Letters to the editor.

Stories of people complaining about wind turbine sounds have circulated for years. As a seasoned professional engineer who has been heavily involved with renewable energy and who has even worked repairing and maintaining turbines for three years, I often considered these stories to be psychosomatic or simply false. During the last few years, I have begun to reconsider as turbine sizes have increased and complaints from folks living near them continue. There is something real going on here.

It is known that wind turbines generate different types of sounds. Mechanical noise stems from sources including the generator, transmission, yaw motors, and pitch control systems. Aerodynamic noise arises from the interaction of the airfoils or blades with the wind. Some of this is in the lower audio and even infrasonic frequencies. While many improvements in airfoil design have been made over the last 30 years to reduce blade noise, some of it remains.

To capture the more consistent higher winds, modern wind towers stand about 295 ft with blade diameters of 328 feet. Not counting a modest boost in height from the concrete base and the nacelle atop the tower, the tip of the blade reaches 459 feet off the ground at its height, and swings down to a level of 131 feet off the ground. As the blades rotate, they will pass through wind moving at different speeds, i.e. wind shear. This can give rise to aerodynamic modulation which generates sounds, particularly at night when wind speeds are more stratified.

Higher frequency noises are weakened or attenuated by structures and vehicles. Lower frequencies are not weakened as much by structures. Indeed, some structures might actually act as amplifiers due to rooms being 1/2 or 1/4 wavelength of the noise signal. Many of the noise complaints arise in the evenings when people are indoors and the air is cooler and more stratified in modest wind conditions.

In October 2018, the World Health Organization (WHO) published guidelines on environmental noise and included wind turbine noise in its report. While the guidelines were published for Europe, they can be "considered applicable in other regions and suitable for a global audience" to quote the executive summary.

For the first time, the WHO commented that there is a link between wind turbine noise and health problems. A report published from the Minnesota Department of Health in 2009 does an excellent job in describing the types and causes of wind turbine noise. This report also notes from a previous study that wind turbine noise is not usually perceived beyond 1/2 mile (2,640 feet) from the turbine site.

Setbacks are distances between objects and a wind turbine. These objects are commonly roadways and structures including occupied dwellings. If the wind farm is approved, then the question of setbacks must be addressed. This is a decision which will have some future-reaching consequences. It is safe to believe that more research and findings concerning wind turbine noise will be brought to light during this time. Ice throw from a blade is one calculation, sound attenuation is another matter altogether. There has been discussion for a 2,500 ft turbine setback from all inhibited dwellings. Based upon past evidence and growing research, this seems like a reasonable proposal though it may not be sufficient in some cases.

Whereas I strongly believe in personal property rights and the pursuit of happiness, a person's ability to make money off their property with a wind turbine should end at the beginning of their neighbor's property line. I don't believe a person has a right to make their neighbors miserable or sick.

For those wanting a little more reading, the executive summary of the WHO report can be found at http://www.euro.who.int/en/health-topics/environment-and-health/noise/p ublications/2018/environmental-noise-guidelines-for-the-european-region -executive-summary-2018

The report on wind turbine noise and public health from the Minnesota Department of Health can be found at https://www.leg.state.mn.us/docs/2009/other/090777.pdf

Sincerely,

Joseph Tillman

(formerly of Assumption, IL)
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Publication:Daily Herald (Arlington Heights, IL)
Article Type:Letter to the editor
Date:May 29, 2019
Words:672
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