Wind Energy

2 B. Lange
point of view. The paper is structured in three main sections: First some
particular problems of offshore measurements are discussed in Sect. 1.2. This
is followed by a section giving examples for meteorological effects specific for
offshore conditions. Their importance for wind power application is shown in
Sect. 1.4, followed by the conclusion.
1.2 Offshore Wind Measurements
In recent years, measurements with the aim to determine the wind conditions
for offshore wind power utilization have been erected at a number of locations
(Barthelmie et al., 2004). Offshore wind measurements are a challenging task,
not only since an offshore foundation and support structure for the mast
are needed, but also because of the challenges to provide an autonomous
power supply and data transfer, the difficulties of maintenance and repair in
an offshore environment, etc. These difficulties lead to high costs of offshore
measurements and often lower data availability compared to locations on land.
Additionally, the flow distortion of the self supporting mast usually requires a
correction of the measured wind speeds for wind profile measurements (Lange,
2004).
Two measurements, from which results are shown in this paper, are the
Rødsand field measurement in the Danish Balitc Sea and the FINO 1 measurement
in the German Bight. The FINO 1 measurement platform (Rakebrandt-
Gräßner and Neumann, 2003) is located 45 km north of the island Borkum in
the North Sea (see Fig. 1.1). The height of the measurement mast is 100 m.
The field measurement program Rødsand (Lange et al., 2001) is situated about
11 km south of the island Lolland in Denmark (see Fig. 1.1) and includes a
50 m high meteorological mast.
1.3 Offshore Meteorology
There are fundamental differences between the wind conditions over land and
offshore due to the influence of the surface on the flow. The most obvious one
is the roughness of the sea, which is very low, but also changes due to the
changing wave field (Lange et al., 2004b). The momentum transfer between
North
Sea
FINO 1 (100 m)
Baltic
Sea
Rødsand (50 m)
Fig. 1.1. The measurement sites Rødsand in Denmark and FINO 1 in Germany