Commercial Wind Turbine Systems and Applications - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 241

Turbines in a wind power station are generally sited in regions that have growing de-
mand for electricity, high COE (power purchase price), high annual average wind speed (6
m/s or more), a reasonable match of higher wind speeds (diurnal and annual) with periods of
peak power demand , proximity to power transmission lines, and access for heavy equipment
and construction cranes.
State and local financial incentives, tax breaks, favorable approval procedures and zon-
ing, or other incentives help project developers by shortening the approval process and allow-
ing a rate of return sufficient to attract private capital investment. Wind power stations are
usually located at uncomfortably windy sites that are normally away from residential areas,
reducing concerns about turbine noise, electromagnetic interference, and visual impacts. En-
vironmental issues involving bird and bat populations and migration can be a concern but
must be considered along with environmental effects from other power generation sources.
The physical arrangement of the turbines within the station depends upon the terrain,
wind directions and speeds, and turbine size. In general, if a site is flat terrain, with winds
predominantly from one direction, the turbines are spaced from .5 to 3.0 rotor diameters
in the cross-wind direction, in rows 8 to 0 rotor diameters apart, as shown in Figure 4-26.
Spacing between turbines on ridgeline projects depends on terrain orientation with respect to
the primary wind direction.
Figure 4-26. Typical arrangement of turbines in a wind power station on flat terrain.
Sizes of wind power stations vary widely. In the United States the average size has
grown with the industry, from 0-MW plants in 984, composed of 00-kW turbines, to most
projects larger than 20 MW by 2007, with an average turbine size of .65 MW. Projects in
the United States are continuing to grow in size and may exceed ,000 MW. In Europe, land-
based clusters of wind turbines are much smaller, typically from 0 to 20 units. However,
much larger stations involving hundreds of turbines are being installed offshore in shallow
water (less than 20 m depth), with some individual machine ratings as high as 5 MW (see
Fig. 2-4).