Wind Energy and the Environment

How environment-friendly is wind energy? What are the effects of wind turbines on the environment, including impact on humans, animals as well as carbon- and energy savings? These questions have to be tackled in an Environmental Impact Analysis (EIA) before building permission is granted. The areas of concern specific to wind development projects are:

• Noise affecting nearby residents,
• Shadow flicker irritating for human eyes (see Shadow Flicker Analysis)
• Visual impactof the development on the landscape (see Visual Impact Assessment)
• Bird collisions

Other concerns that need to be addressed are for development of anciliary buildings, roads and overhead lines as well as increases in traffic during construction. Green Rhino Energy can assist you with the environmental impact study. Please contact us to discuss your requirements.

Noise

Causes

The noise from wind turbines stems from:

Aerodynamic noise

The motion of the blades causes turbulend when passing the tower.

Shaft noise

This is noise from the shaft and bearings moving.

Gearbox noise

Gearbox noise can be reduced by using different tooth profiles on the wheels. So-called spur-gears are the most cost-effective though noisiest. Helical gears and herring bone gears offer a much smoother mesh, resulting in less noise.

Measuring Noise

Noise level is measured in decibels, dB(A), weighted by the sensitivity of the human ear. The sound power is the power of the sound at source, whereas sound pressure refers to the power of the sound at the receiver at a distance. Wind farm noise emission maps show the sound pressure levels at different points and distances from the farm. A modern wind turbine has a sound power level of 90 - 100dB(A). In 350 - 1,000m distance, the sound pressure level is less than 45db(A). which is about the same noise level as turning a page in a book. Generally accepted noise levels for wind turbines are 35db(!) during night and 45dB(!) during the day in front of an open window.

In addition, wind turbines emit infrasounds < 20Hz below human perception - similar to cars and other machinery. To our knowledge, there is no evidence of infrasounds below the hearing threshold to cause physiological or psychological harm.

Shadow Flicker

Wind turbines cast a shadow on their vicinity in direct sunlight. As the blades are turning they may cut through the light beams, causing a flickering effect. The flickering frequency from wind turbines is below 2Hz, not in the range that can cause epilleptic seizures (5 - 30Hz). Nevertheless, the flickering is annoying when at home and awake.

This flicker effect is only experienced in one point for short periods of time, as it requires a certain angle of the sun. There is no standard regulation as to the maximum that hours that are perceived to be acceptable. In Germany, a judge ruled that 30 hours of shadow flicker at a property per year had to be tolerated. This could be seen as a general rule of thumb.

In-dept flicker analysis needs to take into account the whole vicinity of a wind turbine. More...

Visual Impact of Wind Turbines

Due to their height wind turbines are highly visible structures in any landscape. People who live near wind turbines are generally more supportive than people that live far away. However, public opinion may turn if the visual impact of the landscape is ruined by too many turbines. One larger wind turbine may, for instance, be more acceptable than a number of small ones. See the two pictures below for impact. In addition, the rotational speed of larger turbines is lower, not attracting the human eye so much.

Some manufacturers offer turbines painted in grey or bases in green paint (for instance Enercon) in an attempt to make wind turbines blend into the surroundings. Typically, an in-depth visual impact study will be needed.

Bird Collisions and Disturbances

Birds colliding with rotor blades is perhaps the most emotionally charged subject of wind energy. Wind farm developers ought to keep minimum distances to bird conservation areas and breeding grounds of sensitive species. Although it makes for gruesome videos, it needs to be seen in context. According to a study by BUND in Germany, there is statistically one bird death per year for two turbines, or 8,000 bird deaths per year. 5 - 10 million birds die in road traffic and the same number again in power lines.

Furthermore, a study by the Danish Energy Authority on birds' flight paths around offshore wind farm has found that somehow birds are able to avoid wind farms altogether, as most birds do not fly between rows of wind turbines.

Apart from direct bird collisions, the huge pressure changes around wind turbines can cause serious internal damages to some birds, especially bats.

Avoiding bird collisions

The risk of bird collisions can be mitigated by

• increasing the visibility of rotor blades
• using white flashing lights rather than (what is usual) red flashing lights to warn air traffic
• keeping migration corridors free - heavily used migrations paths should not be used.

Other Environmental Issues