Environmental Engineering Reference
In-Depth Information
Figure 8.12
Maintenance work on wind turbines.
Source: REpower Systems AG, Photos: Jan Oelker,
caméléon and Stéphane Cosnard.
8.3.3 Wind Farms
During the pioneering days wind turbines were often erected individually, whereas
today they are almost always grouped in large wind farms (also known as wind
parks). A wind farm consists of at least three turbines but can also have many more.
For example, the Horse Hollow Wind Park erected in 2006 in Texas has 421 wind
turbines with a total capacity of 735 megawatts. These wind turbines are capable
of supplying electricity to 150 000 US households.
The main advantage of wind farms compared to individual turbines is the cost
saving. Planning, erection and maintenance are considerably more economical.
Large wind turbines usually have to have obstacle marking for air traffi c. This
includes a coloured mark on the rotor blade tips and navigation lights that come on
when visibility is poor. With wind farms only the outer turbines have a marking.
This saves money and improves the appearance of the farms (Figure 8.13).
The disadvantage of wind farms is mutual interference. If the wind turbines are sited
close together, they can take the wind away from each other. The effi ciency of the
turbines at the back is then impacted. It is important that suffi cient distance is created
between the turbines in the main direction of the wind so that effi ciency losses can
be minimized. However, effi ciency loss through mutual interference cannot be
totally prevented. Wind farm effi ciency takes into account losses from mutual inter-
ference, which is usually between 85 and 97%. This means that losses between 3
and 15% should be expected.
If wind turbines are too close to housing estates they can have a negative effect due
to noise emission and a shadow being cast as the sun goes down. Turbines should
ideally be erected several hundred metres from the nearest dwellings to avoid creat-
ing this effect.
