The latest AEI Special Report takes a close look (or, listen) to the growing concerns about noise impacts from wind farms.  While it appears that only about 20% of wind farms trigger noise complaints, it is crucial that wind energy developers take a close look at these, to assure they don’t repeat the same mistakes.

As usual with AEI Special Reports, the Wind Energy Noise Impacts report is designed to offer a comprehensive yet concise “ten-minute version” of the issue, with links to more in-depth source material.  It includes sections on wind turbine noise, current regulation, comments from neighbors disturbed by noise, possible factors in noise complaints (atmospheric effects top the list), emerging technology, and links to industry trade groups, government agencies, and advocacy groups, both pro and con.

To read or print the report, visit http://www.AcousticEcology.org/srwind.html 

Some excerpts are below the fold:

From Introduction

Wind energy has long been a favorite of many environmental advocates. No carbon emissions, utilizing a free resource without depleting it in the least, even the potential for distributed generation rather than distant centralized power plants: for many of us, wind was the cleanest of green power sources in our dreams of the energy future.

In recent years, as wind turbines have grown from the small backyard kits that the truly committed built in the 70’s, the reality has made those dreams become less certain. Modern wind turbines are massive structures, hundreds of feet tall, and often constructed in large wind farms that in effect industrialize rural landscapes, from the rolling grassy hills of California, to the vast rangeland of Texas, to ancient ridgelines in the Appalachians, to the commons in rural England. While the trade-offs may be worth it in some areas, the downsides have become more apparent. Resistance to wind farms is often belittled as NIMBY-ism (Not In My Backyard); but at the same time, proponents often slip into oversimplifeid WARYDU rhetoric (We Are Right; You Don’t Understand). If we are to forge a reliable energy future that is respectful of both the environment and the rights of neighbors, we’ll need to move past knee-jerk reactions on both sides, and develop best practices that can ensure that the landscape and local residents don’t become long-term casualties of today’s “Klondike Wind Rush.”

If the thousands of windfarms likely to be built in the coming decade are placed too close to homes, the industry will be faced with an echoing chorus of complaints and resistance for years to come, even if it manages to invent much quieter machines. Better to be conservative, accepting the fact that even occasional atmospheric effects should be factored in to siting decisions today, so as to build a reservoir of good will, rather than a rising tide of complaints. 

From How Noisy Are Wind Turbines? section

It is important to recognize that night-time ambient noise levels in rural areas are often 35dB or lower; so, it is not that hard for wind farms to become a new and dominant acoustic presence. All too often, wind developers tell local planning boards that the turbines will be inaudible, which is rarely the case. Similarly, some investigations of noise complaints come to the conclusion that anomalously high noise levels occur so infrequently that they are insignificant (a recent UK investigation of Amplitude Modulation found that it was only an issue 5-15% of the time). But if temperature inversions or other atmospheric stability effects that cause excessive noise occur just 10% of the nights, that means that nearby residents may find their sleep disturbed 35 nights a year. Is this insignificant? Such questions need to be considered directly, not shunted aside.

From What Some People Are Hearing section

Kevin Bailey stated, “When you are outside working and absorbed in what you are doing, you are OK. If inside, resting or reading, it’s a problem. Forget about sleeping at night. The repetitions would go away, you think that it is gone, and it comes back again.”

 The Stulls said they could move, but they aren’t going to. ‘‘We’re not going anywhere. I just want them to be quiet. I’m not going to jump on the ‘I hate windmills’ bandwagon because I don’t,” Jill Stull said. ‘‘I’m just tired of nobody listening. My point is what is your peace of mind worth? I can’t play outside with my kids back at the pond in the woods because it gives me a headache.” “I know it’s going to make some noise, but a lot of times, it sounds like a jet,” resident Myrle Baum said.

“On a calm day, you come outside and try to enjoy a nice peaceful day, and all you hear is the noise all the time and you can’t get away from it,” said Bob Castel, who has two turbines behind his house. “The first time they started them up, I didn’t know what it was. I was like man, that’s a weird noise. It was that loud.” said Castel.

People think that we are crazy. They drive out around the mountain, stop and listen, and wonder why anyone would complain about noise emissions. But, believe me when we are having noise problems you can most assuredly hear the justification of our complaint. We have had people come into our yard get out of their vehicles and have watched their mouth drop. We have had company stop in mid conversation inside our home to ask, “What is that noise?” or say “I can’t believe you can hear those like that inside your house.”    from Possible Factors in Noise Complaints section

In the daytime, warming air rises, both carrying sound aloft and creating turbulence that scatters turbine noise, as well as creating more ground-based ambient noise that masks turbine sounds. At night, however, when the air stabilizes it appears that noise from wind turbines can carry much farther than expected. This effect can occur with light winds at turbine height and the ground, or, with light winds at turbine height and very little or no wind at ground level.

With light and steady breezes capable of spinning the turbines, but not stirring up much ambient noise, sound levels measured at homes a half mile to nearly two miles away are often 5-15dB higher than models would suggest. It is hard to escape the implication that setback distances may need to be increased in many places where the prevalence of such night time effects suggest sound will often remain at annoying levels for larger distances. It could also help to monitor for synchronous blade patterns and add random variations at night, to mimic the random variations that atmospheric turbulence causes in the daytime. Finally, noise modeling studies should include calculations based on night time stable atmospheres; G.P. van den Berg, whose 2006 Ph.D. thesis is a comprehensive study of these effects, concludes that “With current knowledge, the effects of stability on the wind profile over flat ground can be modelled satisfactorily.” (his measurements indicate that more sophisticated sound models were accurate to within 1.5dB)