Noise and flicker.

The Silence is Gone Forever

I will Never Hear Natural Wind Again

The developer behind the Garden Peninsula industrial wind turbines acknowledged in an interview with Michigan Radio “ there are issues, like the noise”   …… “They make some sound and to some people, at least ostensibly, it’s very aggravating,” he says.” https://www.michiganradio.org/post/wind-energy-cheaper-interest-building-turbines-waning

Read: Facts on wind turbine noise - Australian Perspective

Types of Noise Emitted from Industrial Wind Turbines

Wind turbine noise is associated with mechanical noise and a less studied and understood aerodynamic noise (that includes infrasound).  Mechanical noises originate from turbine components that include gearboxes, generator & hydraulic motors, and fans.  Aerodynamic noise consists of a highly noticeable “swishing” and “thumping” sounds that come from the forces interacting with blades.    That thumping noise is known to be quite annoying and can travel miles away from the wind turbine. 

A new phenomena associated with industrial wind turbine noise is referred to by some as sensation.   This term describes the body’s response to sound that cannot be heard, i.e., infrasound. Sensation is largely felt at infrasound frequencies and is detected by the body and brain differently than audible noise.  This type of noise is not audible and cannot be masked with ear plugs or by other background noise. Some of this noise occurs at a low frequency and is not heard but felt as a vibration.  These other sounds (infrasound and low frequency) are not measured by the wind industry or currently regulated.  Importantly, these pressure pulses or sensations can cause adverse impacts on human’s well-being.  

Turbine noise is also repetitive and has the odd characteristic of what is referred to as amplitude modulation. This noise source causes a greater degree of annoyance.  Turbines also will produce noise when turned off as the generator is left running and wind is still blowing past the blades. [1]

In most situations, wind turbines produce greater noise with an increase in wind speed.  However, the detection of noise in your home or while recreating might be greater on a calm day when there are fewer natural sounds that may mask noise that originates from the turbine. Furthermore, the noise that comes from turbulent inflow and what is referred to as “stall” has a low frequency content which can travel very far distances.[2]  

How is Noise Measured?

Audible noise is measured in units of sound pressure levels called decibels (using A-weighted sound levels, or dBA). The A-weighted sound levels closely match the perception of loudness by the human ear. Decibels are measured on a logarithmic scale which means that a small change in the number of decibels results in a very large change in the amount of noise (https://www.osha.gov/noise).

As seen the following table, an increase of 3 dB represents a doubling of sound intensity.  

Furthermore, dbA (A-weighted measurements) underestimate the perceived loudness, annoyance factor, and stress-inducing capability of noises with low frequency components (one part of wind turbine noise we discussed above), even with moderate amounts of noise.[3]

Is 50 or 55 decibels protective of residents’ well-being?

A police ordinance or other regulation that only limits the sound level to 55 decibels (like in the current Adams police ordinance) at the nearby property line is not protective for residents and property owners and people that may garden, hunt, fish, and do other recreating on nearby land.    

The following table provides an idea of what a quiet evening is in our area (25 decibels) versus noise levels typical of the city and suburbs and recorded at homes located near wind turbines.  And remember from our section above on measuring noise, every 10 dB increase in noise is an increase of a factor of 10 (100 versus 10 for example)!  Further compounding this issue is studies that show wind turbine noise is more annoying than traffic noise.

Studies show the proportion of respondents annoyed by wind turbine noise below 50 dB(A) is larger than noise from other sources (like traffic) (because of the complexity of the wind turbine noise)  

Listen to Wind Turbine Noise

Wind Developer Estimations of Noise. The wind developer has told residents they have computer modeled the noise their turbines produce, and it will not exceed 40 dB at property lines).  However, as we learned earlier, the community will hear this sound level and we know it will not be protective of enjoyment of a good night’s sleep, or while outside on our property, inside our home, and our health.

Please do not trust the estimations made by these computer models.  When we asked Circle Power (in July 2021) to see the report that supports their computer estimated noise estimations, we were told that information is proprietary.  A computer model’s output is only as good as its input.  

An engineering professor who advises us has stated the computer model noise estimates are not perfect and dependent on many, many local geographical and meteorological conditions.  Things like terrain, tree cover, season, time of day, humidity, local weather, wind speed and direction, snow cover and even the type of snow (dry versus wet versus crusty) influence estimated noise levels.  Furthermore, the noise estimation process can simply modify the inputs of the computer model to obtain a result they view as satisfactory.  Therefore, any noise contour maps generated for Circle Power are useless without us being able to examine supporting documentation.

Wind noise researchers have also noted that “more accurate computer models are needed to characterize the various noise sources and provide sound power estimates for each source for use in noise propagation models. The provision of uncertainty estimates for all sound power levels is also important.” 

 What is an appropriate noise level?   Remember from our earlier table, quiet rural nighttime noise levels are perhaps 25 decibels.   To protect surrounding neighbors and our community, the allowable noise level at the property line should be set at 25-30 dBA or less for 10 minutes, not averaged over a whole day or 8-hour period.   

How Loud is too Loud?   Example Proposed Industrial Wind Turbine Siting Sound Limits

 Shadow Flicker

Shadow flicker is the effect of the sun shining through the rotating blades of a wind turbine, casting a moving shadow. It will be worse when the sun is lower in the sky (earlier in morning and later when you want to enjoy the sunset).  It is perceived by a resident as a “flicker” because the fast rotating blades repeatedly cast a shadow that pulses like a strobe light. Thus, it is a nuisance for to community residents.  And note that we are talking about 575-foot turbines so the impact of shadow flicker will be more noticeable compared to earlier turbines that had shorter heights and smaller rotor diameters. https://windexchange.energy.gov/projects/shadow-flicker

The wind industry says shadow flicker is not 24/7 and may only occur at certain times of the day and certain times of the year (we concur).  What they downplay is that it is something rural residents should have to make a part of any part of our day or year.   For example,  we obtained one engineer’s estimate on occurrence of shadow flicker made for a Department of Energy supported presentation on promoting wind energy. In that study, it was determined shadow flicker events at homes would  be along as 49 minutes per day and might happen up to 156 days a year.   https://windexchange.energy.gov/files/pdfs/workshops/2011/webinar_shadow_flicker_priestley.pdf  And that amount of time was downplayed by the presenter.   Is this acceptable to anyone?

Go to the following web sites and see what shadow flicker is like at a house or on one’s property.