Low frequency noise from wind turbines is characteristic of the noise that emanates from large wind farms and is more and more frequently being discussed as a potential health concern for those who live in close proximity to these wind farms.
What Are Wind Farms?
To enable us to put a discussion of this sort into perspective, the question, what are wind farms, must first be first be answered for those of us who are as of yet unfamiliar with them.
A farm is typically an area of land where crops, animals or products, are grown and harvested. In the case of a wind farm, what is being harvested is energy from wind, which is then converted into electricity. On a wind farm, many large wind turbines are constructed or planted close together in a given area. Each turbine is joined with another using a medium voltage, power collection system, as well as a network of communication. In addition to the wind turbines, you will find a number of substations where the electrical current produced by the wind turbines is grown using a transformer to enable a connection to a high voltage transmission system or grid.
The places in Europe that produce wind energy the most are Denmark, Germany, and Spain. On wind farms that are large, there may be as many as several hundred separate wind turbines, which in turn cover a few hundred miles, and often any land in between each turbine is used for the purposes of agriculture. The 2009 World Wind Energy Report states the 2009 growth rate of wind power is the greatest seen since 2001 at 31.7% and that trends are showing that wind capacity is doubling on average, every three years.
What Is Low Frequency Noise?
Low frequency noise from wind turbines can be heard easily on a wind farm. The sound alters depending on if someone is near to an individual turbine or is farther away. As a person moves away from the turbine, the sound consolidates and becomes more focused. Depending on atmospheric conditions, this noise can penetrate the environment for a mile or more.
Noise that is low in frequency refers to sound energy that is in the region below 20Hz. While human listeners may be able to pick out sounds as low as 12HZ, 20HZ is considered to be the normal threshold on the lower end of human hearing. Just about every type of noise that can be found in the world has some sound in this frequency, even though most is not even noticed.
Noise that is put off by a multitude of wind turbines includes noise that can be heard and as well as sounds that cannot be heard and that are found in the infrasound range. In addition, low frequency noise is penetrating in nature and is most often noticed in the absence of competing higher range noises such as at night when things are quieter. In fact, the greater the effort to quieten an environment, the greater the impact of low frequency noise. Turning on a radio will be more helpful in reducing the hearing of low frequency noise than placing a pillow over your head.
What Are The Health Concerns Related To Low Frequency Noise From Wind Turbines?
The health concerns conveyed by those effected by low frequency noise are similar in nature to those of seasickness and like seasickness, effect each individual differently according to his/her sensitivity. Of two people at the exact same location, one may be totally unaware of the presence of low frequency noise while the other may experience heightened stress and anxiety, lack of concentration, pressure in the ears, headaches, dizziness, nausea, and sleep disturbances to name a few of the symptoms reported.
Several reports give substance to claims of those effected by low frequency noise from wind turbines. The first report is by NASA-Langley Wind Turbine Research, 1980-1990. This report documents the results of extensive research conducted by NASA/Langley into wind-turbine noise. The research covered the documentation of sound levels generated by turbine blades in ideal conditions and acknowledged that the sound levels produced could be widely effected by turbulence in the atmosphere, resulting in unsteady blade loading, which in turn could lead to an increase in the sound levels produced.
The results found by the NASA/Langley report were re-confirmed by G.P. Van den Berg in his 2004 report, "Effects of the Wind Profile at Night on Wind Turbine Sound." His report concluded that varying wind gradients can in fact raise sound levels by up to 15dB at night. Yet another 2004 report, "Perception and Annoyance due to Wind Turbine Noise - a Dose-Response Relationship," by E. Pedersen and K.P. Waye J. Acoustical Society of America also addressed this problem. This report found wind-turbine noise to be much more annoying and intrusive than the conventional dBA considerations allow for, and that annoyance levels rise quickly when wind-turbine noise levels exceed 35dBA-38dBA.
Someone, who has never felt the symptoms of sea sickness, air sickness, or sickness from low frequency noise, may find it difficult to understand the nature and scope of their effect on those who are sensitive. It is not unusual for the reports of illness from these causes to be scoffed at. As well, as these reports have a monetary effect, the need to prove that they do not exist is also well understood. That does not, however, mean that they do not in fact exist. When even NASA acknowledges there is a problem, then steps begin to be taken to help alleviate the suffering of those who are effected.
Some steps that have been recommended are:
- Wind turbines to be located no closer than 2.0 miles from human habitation in mountainous terrain.
- Wind turbines to be located no closer than 1.25 miles from human habitation in flat terrain conditions.
- The replacement of blade systems on older wind-turbines with ones designed to be upwind of the tower and placed at a greater distance from the tower to lower the incidence of airflow disturbances occurring between the blades and the tower.
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