This posting was originally on my amherstislandwindinfo.com site and I finally copied it over to here.
The most complete measurement of wind turbine sound I’ve found so far (as of mid 2008) is from the Mars Hill Wind Farm. When built it was the largest wind farm in New England, with 28 1.5 MW turbines. It has also been one of the most contentious, with many complaints from the mis-led neighbors. In response to the complaints, an independent consultant was hired to measure actual noise levels during normal operations. The “2nd Quarter” report was published on November 2, 2007, and most of my numbers are from that report. The “3rd Quarter” report was published April 11, 2008 and didn’t reveal any important new facts.
The reports are long and technical, and they are on both this site and the original marshillwind.com site, which has since been taken over by someone else. To me the following two tables, one from November 2007 and the updated table from April 2008, are useful in compressing the entire reports into one page. These charts list the different testing locations and a summary of the noise levels found at each. The second column provides the peak noise levels that were attributed to wind turbine operations. Maine, in its infinite wisdom, allowed the Mars Hill farm to produce 50dbA at a neighbor’s home, a full 5dbA above the normal Maine limit. One site, MP-1, is above even that very generous limit. The owners at MP-1 must be miserable. But most noise regulations and recommendations have a 40dbA max, and almost all of the locations experience noise above that. Also notice that the pre-construction model estimates are quite far under the actual results.
2nd Quarter Table
3rd Quarter Table
To get some sense of how far away from the turbines you have to be to get to down to the WHO-recommended 40dbA, I’ve sorted the rows by distance, obtained a few additional numbers, and eliminated a couple of locations where the 2ndQ numbers looked invalid (one meter looked like it was inconsistently high, and another location suffered from a lawn mower), leaving six valid-appearing locations. One of the purposes of this study was to compare the pre-operational computed levels with the actuals, and the last column provides the original estimate, which was always under the measured result. This is true even though the models are supposed to represent the “worst case” and the measured results were the average of a 24-hour period and not a not peak period.
|Location||Distance(m) to nearest turbine||LAeq average||LA1 average||Comments||Non-farm noise level||Modelled Estimate|
I included the LA1 averages because the WHO Guidelines recommend its use as more representative of human disturbance for the type of noise that wind turbines produce.
Also note the deltas between the non-farm noise level and the LAeq levels. That is how much noise, on a fairly constant basis, is added to the background level. Given that every 6db is a doubling of sound levels, the closest site had it’s background quadrupled, while even the furthest had its background level more than doubled. The experience at Mars Hill provides a fair amount of support for a minimum setback of 1500 meters.
I obtained the Mars Hill studies from marshillwind.com, the site maintained by the energy company, and can be obtained from there, until they take them down.
Backup link, 2nd quarter Report
Backup link, 3rd quarter Report
Here’s an interesting comment letter concerning how the modeling was done.