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October 10, 2011

Wind Turbine Noise

Noise from utility scale wind turbines and wind farms has resulted in numerous complaints from nearby residents worldwide. Many who have studied this problem have concluded that the only safe solution is to establish setbacks of at least a mile and a quarter.

Once installed, there is nothing that can be done to mitigate the noise short of shutting the turbine down. Furthermore, given the fact that the noise level is constantly changing as a function of wind speed and direction, collecting data to prove compliance is extremely labor intensive and prohibitively expensive.

In Falmouth, Vinalhaven and elsewhere it has taken more than a year to make a determination. Incredibly, the MassDEP is inclined to follow the common practice of using the LA90 metric for all sound measurements. By design, this system registers only the quietest sound levels present 10% of the time. It fails to measure 90% of the Amplitude Modulation (AM), which is the real source of complaints and happens to be the most noticeable and annoying characteristic of wind turbine noise. MassDEP has accepted the argument that measuring the peaks of AM requires an expensive data collection protocol.

In order to gain permit approvals, wind industry proponents insist on the use of supposedly “scientific” methods, such as that contained in the New Zealand Standard NZS 6808:2010. It is used to determine safe noise levels on a case-by-case basis. However, such standards suffer from a number of assumptions. These include a limited range of data in the case of published noise emission reports and the exclusion of relevant data when modeling is used.

A major source of error is the accuracy of the published noise emissions from a given wind turbine. The published figures are derived using the IEC 61400-11 standard, which carries no warranty that the figures are maximum levels. The main purpose of IEC 61400-11 is to provide reproducible results at wind speeds between 6 and 10 meters per second for comparison

Computer modeling, used to calculate the propagation of wind turbine noise, assumes the noise originates as a point source at hub level. In fact, the noise of interest is generated by the blades at their extremities. This is another cause for miscalculation.

These assumptions result in grossly under-predicting, by orders of magnitude, noise levels at the various receptor sites around a turbine.

The complexities of the so-called scientific method favored by the wind industry are open to manipulation and abuse. Add to that the next-to-impossible task of proving post-construction compliance. This leaves, as the only reasonable approach, the acceptance of the expert studies that recommend a setback distance of a mile and a quarter or more as the best way to protect the public from the extreme annoyance, and the ill health effects from wind turbine noise.

The fact that some people, who live in close proximity to wind turbines, can tolerate the noise without apparent annoyance or ill effects is interesting. However, this does not diminish the many claims of those whose experience is to the contrary. There can be any number of explanations as to why people are affected differently, but for now the focus needs to be on the significant number of people living within a mile of wind turbines who not only find them annoying, but argue that the noise is the cause of sleep disturbance, headaches and other ailments.

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