In this section I will zero in on the ways the complexities of the Noise Basics and the looseness of the Noise Regulations allow the wind industry, abetted by the government, to legally destroy people’s homes and health. Some may consider the previous sentence pretty strong, but after all the truly sad stories I’ve read – numbering in the hundreds, from all around the world – I think it is entirely justified. Obviously it is in the interests (at least in the short-term) of the wind industry developers to try to disregard or nullify as many protections as they can. The governments nominally are in the business of protecting their constituents, but it seems that many governments have either forgotten this or simply don’t have the means to do so. Money plays a part, as governments are always eager to get new sources of income and the developers are eager to promise same. A second, more sinister, problem exists when the government responsible for making and enforcing the rules also has the goal of increasing wind energy. Britain’s DECC – that’s Department of Energy and Climate Control – opted to pursue wind energy at the expense of the citizens.
The sections below show the major ways (that I know of) of circumventing the intent of the noise regulations. All of these circumventions occur before the construction even begins; once the turbines are up seldom are there cases where they’ve been shut down, no matter how serious the problems.
From a noise perspective, perhaps the single most important activity is modeling the project’s projected noise effects on the neighbors. Most projects hire a consultant who takes ambient measurements, maps out where the participants and non-participants are, plays around with siting the turbines and comes up with a noise topological map of the project. As long as the non-participants are all outside of, for example, the 40-dbA contour line the government is likely to accept those sitings as permissible. And once they are built they are never moved and seldom shut down regardless of their actual noise generation, so the siting map becomes critical.
While creating the model the consultant needs to make a number of judgments about how to set all the parameters up. This is especially evident when considering what constitutes the “worst reasonably foreseeable circumstances”. All of these decisions can significantly alter the siting, and since I’ve seldom seen these decisions documented in any noise assessment, I pretty much have to assume they were made to best favor the consultant’s employers – the wind developers.
An easy way to see if the modeling is being done in an accurate manner is to measure the noise and compare it with what the model predicted. As you might guess – I wouldn’t be writing this without some evidence – whenever there are complaints and the noise is measured it is quite often above what the model predicted. Here’s some samples.
- Ashbee measurements were in the mid 60’s, some 15dB over projections.
- d’Entremont measurements were in the 50’s, some 15dB over original claims from the developer.
For the really curious, here’s some rather technical studies that explore how choosing one of these parameters, propagation, can affect the results – enough to make a major difference to a neighbor.
- Probst, Methods for the Calculation of Sound Propagation, a general look at the issues.
- Kakiski and Duncan, Propagation Modeling Parameters for Wind Power Projects.
Because most noise regulations predate wind turbines, there’s an implied assumption here that wind turbine noise is essentially the same as any other noise and can be regulated with similar rules. Unfortunately, there’s growing evidence that the “whoosh” is unnatural enough and pervasive enough that it requires special treatment. The combination of low frequencies and the pulsing character of the noise is not easily blocked by walls or alternative sounds, like running a fan. Most people can adjust to noises over time, but there’s growing indications that people never adjust to wind turbine noise – in fact for some it gets worse over time.
Eja Pedersen documented the responses of residents to different levels of wind turbine noise and compared these reactions to other equally-loud sources of noise. She found that wind turbines create more complaints at lower levels than any other source, i.e. traffic, trains, planes etc., as summarized by the chart below.
- Van Den Berg article, Perspectives on Wind Turbine Noise.
- Pedersen Paper, Human Response to Wind Turbine Noise
- Pedersen and Waye, 2003, Perception and Annoyance. Above 35 dBA, annoyance grows more quickly with turbine noise than any other kind
- Pedersen Paper, Turbine Noise, a Review
It is well known that as the wind blows harder wind turbines produce more noise, enough so that the setbacks would have to be quite large to keep the noise at the neighbors under typical limits. It is also well known that the wind itself produces more noise as it blows harder. At one time many jurisdictions reasoned that the higher noise from the wind “masked” the higher noise from the turbine, thus the noise limits should be raised during windy times.
Several years ago, Dutch residents who were close to a German project were complaining that the noise was quite loud, much louder than the models and current acoustic theory would have predicted. A Dutch PhD candidate, van den Berg, was curious to find out what caused this discrepancy. He discovered that most of the complaints were in the evening and at night. He measured away, and discovered that the noise levels really were higher than predicted, especially during these times. At that time, Germany allowed the higher limits in stronger winds. But van den Berg’s measurement discrepancies were during light wind periods, typical of evening conditions. Then he noticed that the turbines seemed to be spinning at full power (the project operator was not being cooperative, so he had to estimate their output) even when the ground wind speed was close to zero. As a consequence, they were producing full-power noise that was not being masked out by ground winds.
It is well known in meteorological circles that after the sun goes down, the atmosphere – no longer being heated from below – becomes more stable, no longer mixing vertically. This allows wind speeds to vary with altitude, becoming stratified. It is common for winds at modern turbine heights to be strong while winds on the ground are weak, and there were already formulas to describe this effect. To make matters worse, quite often the winds actually stratify, forming boundaries that also trap noise. Do you remember our discussion of cylindrical vs. hemispherical dispersion, and how it changes the rate that noise decreases? This wind shear effect can be a surprisingly big deal, causing much higher-than-expected noise for recipients, to the point where health effects are a concern, not to mention annoyance and sleep disturbance. Presently (March 2009) only Ontario and New Zealand still permit the use of masking.
- Amherst Island’s John Harrison, letter on wind shear.
- van den Berg Article, in the Journal of Sound and Vibration.
- Archer Paper, distribution of winds.
- Smith Paper, NREL, Evaluation of Wind Shear.
- Schwartz Paper, NREL, Wind Shear Characteristics.
- van den Berg Paper, The Sounds of High Winds, technical details about wind shear. The non-technical parts are very readable, and well worth the time.
- Final Ramakrishnan Report, Ontario’s attempt to debunk van den Berg.
- Harrison Debunking to Ramakrishnan’s debunking.
Measuring Ambient Levels
As part of many projects a consultant is hired to take pre-project sound measurements in order to establish background, or ambient, noise levels in the neighborhood. Since many noise regulations are based on ambient levels plus the project’s noise, it is important to accurately establish the ambient level. If the original background level is high enough, the developer can justify higher noise emissions and thus more turbines.
Typically a consultant is hired who puts noise recording devices at various points in the proposed farm. The results are recorded and often published and then are used to help make siting decisions. In upstate New York one Mr. Bolton noticed that many of these readings were much higher than he would have expected. Upon researching the reasons, he discovered that the consultant did not properly shield the microphone from wind noise. He wasn’t talking about shielding the noise the wind makes in the trees; he was talking about the noise the wind makes as it strikes the microphone. Even with the foam cover, the noise as recorded by the meter increases quite dramatically when the mike is exposed directly to wind. Bolton compared the wind speed with the noise readings and found a very high correlation, pretty much in line with the specs published by the meter manufacturer.
The consultant made a mistake, right? You might think – so what? But this is a very convenient mistake for the developer who, you should recall, paid the consultant. This very same “mistake” was made in the Wolfe Island measurements, and is being used to justify sitings that would otherwise not be proper. It would also make it harder, if not impossible, for a truly injured resident to prevail in court.
The previously mentioned John Bolton in NY has done a lot of research on this “mistake” and has written two papers, both of them in response to developers’ badly-done environmental studies.
- Bolton Reply, Wind Turbine Noise Analysis Errors
- Bolton Reply, Evaluation of Supplemental Environmental Noise Analysis
In addition to the wind noise issue, it is certainly possible for the noise consultant to take samples that overstate the ambient noise level, simply by their placement or timing. In Cape Vincent, NY, the pre-construction ambients were so high that concerned citizens hired an independent consultant, a Mr. Schomer, to do a second study. Almost predictably, he found the original ambients were too high. The originals were done by a Mr. Hessler, who has done a lot of work for wind developers, and I assume would like to continue doing so. Since it is in their interest to get the ambients as high as possible, it is also in his interest. Mr. Schomer tries to remain civil, but there’s little doubt how he regards Mr. Hessler. Reading just the executive summary is enlightening.
Back in my Basic Acoustics post, I discussed how the dimensions of both the source and the medium affect how sound dissipates. When a noise modeling program is used, it must make some assumptions about how the noise will disperse, and these assumptions have a direct impact on how the noise topo map is drawn. Modeling programs differ in their sophistication. Some allow point and line sources, some allow area sources. Some allow hemispherical, cylindrical and in-between noise dissipation. As far as I know, the program used for many projects, including Tug Hill and Wolfe Island – Cadna/A, from Scantek, Inc. – is not sophisticated enough to allow for all the complications of the real world, especially the complications of wind turbines.
One issue that seems important to me is the assumption of a point source. In the case of wind turbines typical values are 100 to 110 dBA, and are always assumed to originate at a point. This is in spite of studies that show that most of the noise is generated by the blades, radiating away from them at an angle both in a forward and backward direction. The picture below shows a picture of the noise, and Oerlemans and Bowdler provide more details.
If the blades were small or if you were far enough away this simplifying assumption might be reasonable. But when you are only 350 meters away and the blades have a diameter of almost 100 meters it is not reasonable. A series of pictures might make the problem clearer. Below I show the top view of a turbine with a small circular hub in the middle. The normal simplifying assumption is that all the noise radiates from this small hub. In reality, as shown in the picture above, most of the noise radiates from the blades. Further, the noise departs at an angle to the blades’ disk, as shown in Bowdler and the pictures below, which are a top-down view. If the noise was perfectly contained within the dashed lines it would act like a laser beam and wouldn’t dissipate very quickly at all. Obviously there is some spreading over 3 dimensions as shown, but it no longer spreads evenly as though from an idealized point.
Just as an exercise, I’ve drawn the spread in a 25% ratio below. I have no basis to choose 25%, and obviously the spreading goes beyond that, but I’d bet this isn’t totally divorced from reality. This assumed spread would lead to a prediction that the noise directly under the turbine would be less than out in front of it, which does agree with observations.If we then extend the lines back from the disk they would establish a new virtual source point 200 meters behind it. Since the sound spreads in both directions there would actually be two virtual points, on each side of the disk, but I’m only showing one.
If we then run all the models using the new virtual point as the source, we would get a different set of noise levels, one that arguably is closer to reality than the current methodology, as shown in the chart below. (click to see the entire chart)
Now, obviously, this is all a mental exercise, and the reality of my specific assumptions is debatable. What is not debatable is that the simplified models that are used to place these large and permanent structures are not accurate, and experience has shown that people are suffering as a result.
As a further complication, the large area where the noise originates may well lead to additional turbulance and shadowing, which in turn would almost certainly lead to more noise and amplitude modulation (the thumping and swishing that neighbors complain about).
- Moriarty Paper, 0.7mb, more details on modeling parms.
- Kaliski Paper, 1.2mb, more details on modeling parms.
- Mars Hill Comment Letter, Cadna/A is mentioned, among other things.