Quantifying evidence either way can be pretty tough to measure. Sensitivity to noise and shadow flicker are fairly subjective. They differ from person to person, from place to place, and from wind turbine to wind turbine.
Measuring noise and shadow flicker also depends on many factors - wind speed, flow, and direction, terrain, latitude, sun position, whether there was a pre-construction baseline of noise measured at the site, and so on. All of which makes these phenomena hard to study.
However, here is what we do know:
- Air quality. By improving air quality, wind energy has positive benefits for human health, especially compared to electricity generated from fossil fuels.
Wind power does have emissions associated with manufacturing, transporting, and installing turbines (as with any electrical generation). However, when operating wind turbines emit no greenhouse gases or other pollutants like nitrous oxides, sulfur oxide, mercury, etc.
- Sound. Sound (noise) from turbine operation comes in three main forms – broadband, tonal, and low-frequency. Improved engineering of large wind turbines has all but eliminated mechanical sounds from gearboxes, etc.
Complaints tend to center on the sound of turbine blades interacting with wind. A wind turbine creates sound pressure of 50-60 dB(A) (a decibel measurement) at 40 meters. For comparison, a busy office measures 60 dB(A), and nighttime ambient noise in the countryside (leaf rustles, etc.) measures between 20-40 dB(A).
Also, smaller turbines can be noisier. Lots of research dollars have
recently been poured into making the big ones quiet, and keeping them
from having an impact on flying wildlife. The same has yet to be
consistently done for the smaller turbines.
Of course, because of their scale, smaller turbines are also more
likely to be installed close to homes, schools, and businesses.
- Vibrations. Generally, the impact of low-frequency vibrations on human health is not well-understood. For example, some people could easily live next door to a subway and never notice the vibrations, but others could not. However, just because the problem is hard to understand doesn’t mean it does not exist.
- Shadow flicker. Shadow flicker is caused by turning turbine blades, which create variations in shadow patterns. It is a problem in northern Europe (especially in winter, due to lower sun angles at a higher latitude) but is not considered to be so in the U.S.
While it can be annoying for some, a wind turbine’s flicker frequency (0.6-1.0 Hz) is physically harmless to humans. Only frequencies above 10Hz can cause seizures in humans. Strobe light frequencies are between 3 Hz and 10 Hz.
- Lighting. Something that has not been well studied: the possible effects of wind turbines’ nighttime lighting on human health. Due to FAA regulations, all towers must be lit from dusk to dawn. This could possibly cause poor sleeping patterns for homeowners who live too close.
People who live close to cell phone or other communications towers (and right now there are many more of those than wind turbines) complain about this problem.
- Zoning. While the health effects of wind power are not yet known - and may never be known with certainty - zoning and siting guidelines can do a great deal to mitigate the possible annoyance issues.
Some counties have addressed these issues. However, most large wind installations go into rural areas, where zoning of any kind is frequently scarce.
- Transmission Lines. Transmission lines and upgrades go along with wind development. Authorities have debated whether high speed transmission lines have an impact on human health but as yet there seems to be no conclusive evidence that they are harmful.
Setbacks from buildings, etc., would help mitigate such concerns.
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