Barthelmie, RJ

Presented at the European Wind Energy Conference and Exhibition, July 2001, Copenhagen
When the wind speed dropped below 4 m/s the
turbines stopped generating. At other times the
measurements were stopped by rain when the SODAR
does not give reliable signals. Despite these difficulties,
wind turbine wakes were clearly measured. These were
indicated by a decrease of wind speed between heights of
30 and 60 m when the turbine was operating and an
increase in the profile at these heights when the turbine
was stopped manually. Figure 7 shows preliminary
results comparing the free stream wind speed profile
measured to the west of the wind farm and the wind
speed profile behind wind turbine 1W at a distance of
approximately 140 m (4 rotor diameters). Both profiles
have been normalised with the free stream wind speed
measured at 50 m on the offshore meteorological mast.
Analysis of the experiment data are underway and will
focus on single wakes (although double wakes were also
measured) at distances between 1.5 and 6 rotor
diameters.
12
April 2001
22 23 24 25 26 27
Height (m)
100
80
60
40
20
0
Free-stream
Wake
.
0.6 0.8 1 1.2 1.4 1.6
Normalised wind speed
Wind speed (m/s)
8
4
0
Sailing times
Figure 6. Wind speed during the SODAR experiment
(22-27 April 2001).
Figure 7. SODAR measured offshore wind speed profile
(normalised with mast measured wind speed at 50 m).
4 SUMMARY
The ENDOW project focuses on the evaluation and
development of wake models for use in an offshore
environment. Boundary-layer measurements from
existing offshore wind farms are being used for the
evaluation. Results from an experiment with a boat
mounted SODAR are also providing near-wake wind
speed profiles. Additionally boundary-layer models are
being improved for use with wake models to improve
prediction in the coastal zone and over the area of large
offshore wind farms.
3 FUTURE WORK
The main focus of the project is to incorporate
improvements in wake and boundary layer models within
design tools for use in offshore environments. At this
time three main components are envisaged:
1) Coupling between WA S P to provide a regional
climatology and a local scale model (CDM2) with
stability, wind-wave-roughness and internal
boundary-layer sub modules.
2) Production of an enhanced wake model. This task is
mainly directed towards selection of suitable codes
according to performance, input requirements and
computational feasibility.
3) Since grid connections are a major expenditure in
offshore projects, minimisation of these costs will be
a significant factor in the overall design optimisation
of offshore wind farms.
The utility and efficiency of the design tools will be
evaluated at a number of planned offshore wind farms.
5 ACKNOWLEDGEMENTS
Financial support for this research was given in part
by the European Commission's Fifth Framework
Programme under the Energy, Environment and
Sustainable Development Programme. Project
Reference: ERK6-1999-00001 ENDOW (Efficient
Development of Offshore Windfarms). Additonal
funding was supplied by NOVEM for Ecofys and ECN.
6 REFERENCES
1. Barthelmie, R.J., M.S. Courtney, J. Højstrup and
S.E. Larsen, J. Wind Eng. & Indust. Aerodyn., 1996.
62: p. 191-211.
2. Rados, K., et al. EWEC. 2001. Copenhagen.
3. Barthelmie, R.J., B. Grisogono and S.C. Pryor, J.
Geophys. Res., 1996. 101: p. 21,327-21,337.
4. Smedman, A.S., U. Hogstrom and H. Bergstrom,
Wind Eng., 1996. 20: p. 137-147.