Environmental Engineering Reference
In-Depth Information
Figure 8.13
Wind parks.
Source: REpower Systems AG, Photos: Jan Oelker.
Because of the rules on required distances, it is already becoming increasingly dif-
fi cult to fi nd good sites for new wind farms in Germany and Denmark. Therefore,
a greater planning effort is being made in the areas that are still available: the North
Sea and the Baltic.
8.3.4 Offshore Wind Farms
With offshore wind farms the turbines are sited directly in the water. For maximum
effectiveness the depth of the water should not be too great and the turbines should
not be too far from the coast. Along with the enormous size of available area, off-
shore use also provides other benefi ts: the wind blows stronger and more evenly on
open seas than on land. The power output per wind turbine increases at offshore
sites and can be up to 100% higher than on mainland sites.
Offshore wind turbines differ relatively little from onshore ones. Generally, offshore
turbines do not require a good deal of maintenance. Access to wind turbines on high
seas is not possible in bad weather or when the sea is rough. Special ships are
required for major maintenance work but can only be used if the water is relatively
calm. Because offshore wind turbines stand in salt water, all components have to
be well protected and corrosion-resistant.
Special ships with cranes erect the wind turbines out at sea (Figure 8.14). Special
foundations are used to anchor the wind turbines to the seabed. With monopile
foundations, a large steel pipe is driven many metres into the seabed. The stability
of the bottom is important, and a more secure foundation is needed if the ground is
too soft, which increases the cost. This problem may make it economically unfea-
sible to erect projects in shallow water.
Connecting offshore wind farms to the grid is also more diffi cult than on land. Sea
cables link the different wind turbines to a transformer station, which looks like a
small drilling platform. The transformer station converts the electric voltage of the
