5.3 CURRENT
DEVELOPMENTS
5.3.1 Wind Farms
A group of 10-50 wind turbines at a
single site is known as a wind farm. They must however
be spaced apart because the low speed wake from each turbine
is likely to interact with another machine downstream.
The shearing action of the surrounding wind will however
eventually accelerate the air again, and a typical spacing
of about 10 rotor diameters is needed. The total size
of the farm is also limited by the larger scale effect
of slowing down the wind boundary layer, even if the local
geography would allow it to be larger, so that a typical
maximum power rating for a complete wind farm on land
may be only 30 MW.
Although
California led the way, the most significant recent wind
farm installations are in Europe (fig 5.14). Virtually
all of these are on land and use horizontal axis propeller
type machines, with Danish manufacturers in the forefront.
Turbine sizes have been steadily increasing, and range
from 250 kW up to 1MW. It is particularly notable that
the leaders are Germany and Spain, which are not the countries
with the greatest wind energy resource in terms of annual
average wind speeds, but have large areas of land available.
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Figure
5.14 World Wind Power Capacity 2003 (34 GW total)
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Renewable Energy Sources
