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Title-Wind as alternative energy source
  Wind Turbines and the Environment: Landscape
 

Hints About Landscape Architecture and Wind Turbines

   
 

Kappel Wind farmKappel Wind FarmPhotograph Søren Krohn © 1999 DWIA

Wind turbines are always highly visible elements in the landscape. Otherwise they are not located properly from a meteorological point of view.

The image to the left shows the wind farm at Kappel, Denmark. It is perhaps the most aesthetically pleasing layout of any wind farm known to this author. The shape of the dike along the coastline is repeated in the line of turbines.

There is one disturbing element in the picture above: The single turbine next to the farmhouse, which interrupts the otherwise smooth pattern of turbines. (That turbine was there before the wind farm was built).

 
 
 
 
 
 
 
   
 
 
 
 
 
 
 
 
 
 
 
     
    Simple Geometrical Patterns
     
   

In flat areas it is often a good idea to place turbines in a simple geometrical pattern which is easily perceived by the viewer. Turbines placed equidistantly in a straight line work well, but the example in the picture above may be even more elegant, where landscape contours invite such a solution.

There are limits to the usefulness of being dogmatic about using simple geometrical patterns, however:

In hilly landscapes it is rarely feasible to use a simple pattern, and it usually works better to the the turbines follow the altitude contours of the landscape, or the fencing or other characteristic features of the landscape.

Whenever turbines are placed in several rows, one will rarely be able to perceive the pattern when the park is viewed from normal eye level. Only when one is standing at the end of a row, does it really appear as an ordered layout. In the next panorama picture, you will probably only be able to discern three rows of turbines, while the rest appear to be scattered around the landscape. Photo from Naesudden, Gotland, Sweden, Courtesy of Suzanne Clemmesen Photograph © 1997 Suzanne Clemmesen

   
   
   
   
   
   
   
   
 
 
 
 
 
 
 
     
    Light Grey Paint
     
    The picture above shows one of the larger groupings of Danish built wind turbines at Näsudden on the island of Gotland in Sweden. The grey paint on the turbines make them blend well into the landscape.
   
     
    Size of Wind Turbines
     
   

Large wind turbines enable the same amount of energy to be produced with fewer wind turbines. There may be economic advantages to this, such as lower maintenance costs.

From an aesthetic point of view, large wind turbines may be an advantage in the landscape, because they generally have lower rotational speed than smaller turbines. Large turbines therefore do not attract the eye the way fast-moving objects generally do.

   
   
 
 
     
    Sound from Wind Turbines
    Noise is a Minor Problem Today
     
    It is interesting to note that the sound emission levels for all new Danish turbine designs tend to cluster around the same values. This seems to indicate that the gains due to new designs of e.g. quieter rotor blade tips are spent in slightly increasing the tip speed (the wind speed measured at the tip of the rotor blade), and thus increasing the energy output from the machines.
   
   
   

It thus appears that noise is not a major problem for the industry, given the distance to the closest neighbours (usually a minimum distance of about 7 rotor diameters or 300 m = 1000 ft. is observed).

The concepts of sound perception and measurement are not widely known in the public, but they are fairly easy to understand, once you get to grips with it. You can actually do the calculations yourself in a moment.

   
   
 
 
     
    Planning Wind Turbine Installation in Regard to Sound
     
   

Wind Turbine Sound Map Fortunately, it is usually reasonably easy to predict the sound effect from wind turbines in advance.

Each square measures 43 by 43 metres, corresponding to one rotor diameter. The bright red areas are the areas with high sound intensity, above 55 dB(A). The dashed areas indicate areas with sound levels above 45 dB(A), which will normally not be used for housing etc. (We get to the explanation of the sound level and dB(A) in a moment).

As you can see, the zone affected by sound extends only a few rotor diameters' distance from the machine.

   
   
   
   
   
   
   
   
   
 
 
 
 
   
   
   
   
   
   
     
    Background Noise: Masking Noise Drowns out Turbine Noise
     
   

No landscape is ever completely quiet. Birds and human activities emit sound, and at winds speeds around 4-7 m/s and up the noise from the wind in leaves, shrubs, trees, masts etc. will gradually mask (drown out) any potential sound from e.g. wind turbines.

This makes it extremely difficult to measure sound from wind turbines accurately. At wind speeds around 8 m/s and above, it generally becomes a quite abstruse issue to discuss sound emissions from modern wind turbines, since background noise will generally mask any turbine noise completely.

   
   
   
   
     
    The Influence of the Surroundings on Sound Propagation
     
    Sound reflection or absorption from terrain and building surfaces may make the sound picture different in different locations. Generally, very little sound is heard upwind of wind turbines. The wind rose is therefore important to chart the potential dispersion of sound in different directions.
   
   
     
    Birds and Wind Turbines
     
   

Birds often collide with high voltage overhead lines, masts, poles, and windows of buildings. They are also killed by cars in the traffic.

Birds are seldom bothered by wind turbines, however. Radar studies from Tjaereborg in the western part of Denmark, where a 2 megawatt wind turbine with 60 metre rotor diameter is installed, show that birds - by day or night - tend to change their flight route some 100-200 metres before the turbine and pass above the turbine at a safe distance.

In Denmark there are several examples of birds (falcons) nesting in cages mounted on wind turbine towers.

The only known site with bird collision problems is located in the Altamont Pass in California. Even there, collisions are not common, but they are of extra concern because the species involved are protected by law.

A study from the Danish Ministry of the Environment says that power lines, including power lines leading to wind farms, are a much greater danger to birds than the wind turbines themselves.

Some birds get accustomed to wind turbines very quickly, others take a somewhat longer time. The possibilities of erecting wind farms next to bird sanctuaries therefore depend on the species in question. Migratory routes of birds will usually be taken into account when siting wind farms, although bird studies from Yukon, Canada, show that migratory birds do not collide with wind turbines (Canadian Wind Energy Association Conference, 1997).

   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
    Sources:
    http://www.windpower.org/en/tour/env/index.htm
    http://www.windpower.org/en/tour/env/sound.htm
    http://www.windpower.org/en/tour/env/birds.htm