Basics of Renewable Energy Supply - Renewable Energy: Technology, Economics and Environment - page 60

tion of concrete sites, these interdependencies are likely to shift due to local influ-
encing parameters; this is particularly true for low mountain ranges with a very
complex topography.
Therefore Fig. 2.29 additionally shows the distribution of the mean annual
wind velocity for a small terrain with a complex topography at 50 m above
ground. The inserted contour lines clearly delimit the hills and valleys in the area
presented in Fig. 2.29. In the given example, the mean annual wind velocity in the
valleys has been below 4 m/s due to shading effects. As a contrast, there is free
flow against the hilltops; thus in these areas higher wind velocities of above 6 m/s
can occur at times. Additionally, the moved air masses are accelerated when over-
flowing the hill formations. This aspect and the nature of the flow against the hills
lead to these comparatively high wind velocities on mountain tops. In contrast, the
mean wind velocities for plains are between 4 and 5 m/s.

7 7 0 770

Jahresmi ttlere
Windgeschwindigkeit
in 50m über Grund
1 - 4,0 m/s
4,1 - 4,5 m/s
4,5 - 5,0 m/s
5,1 - 5,5 m/s
5,5 - 6,0 m/s
6,1 - 6,5 m/s
>6,5 m/s
Höh enl inien

Jahresmittlere
Windgeschwindigkeit
in 50m über Grund
1 - 4,0 m/s
4,1 - 4,5 m/s
4,5 - 5,0 m/s
5,1 - 5,5 m/s
5,5 - 6,0 m/s
6,1 - 6,5 m/s
>6,5 m/s
Höh enl inien

Values in m/s
1.0 - 4.0
4.1 - 4.5
4.6 - 5.0
5.1 - 5.5
5.6 - 6.0
6.1 - 6.5
> 6.5

Values in m/s
1.0 - 4.0
4.1 - 4.5
4.6 - 5.0
5.1 - 5.5
5.6 - 6.0
6.1 - 6.5
> 6.5

600 600

500 500

Fig. 2.29 Example of wind velocity distribution at 50 m above ground in a complex area

Due to their inherent indistinctness, such maps showing the regional distribu-
tion of the long-term mean annual wind velocity only serve to initially identify
areas, and potential wind sites, with a high wind energy supply. For a concrete site
evaluation they cannot replace the measurement of the local wind velocities, as
these depend to a large extent on the surface roughness of the site, potential obsta-
cles in the local environment, the relief of the area, and the altitude above ground.
These parameters are very dependent on local site conditions. However, the wind
velocity distribution maps shown exemplarily in Fig. 2.29, enable the identifica-
tion of areas and possible sites for which more detailed examinations and meas-
urements of the wind conditions make sense.

Time variations. Using the example of a site in North Germany, Fig. 2.30 shows
the annual course with monthly and daily mean wind velocities. Additionally two
daily courses with mean hourly wind speeds (30 th and 300 th day of the year) and