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Improvement of power curve measurement with lidar wind profiles. R Wagner, M Courtney, J Gottschall , P Lindelöw-Marsden EWEC 2010 20-23 April 2010 Warsaw, Poland. Outline. Motivation Experimental setup Classification of wind profiles Kinetic energy flux approximation - PowerPoint PPT Presentation
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Improvement of power curve measurement with lidar wind profiles
R Wagner, M Courtney, J Gottschall, P Lindelöw-Marsden
EWEC 201020-23 April 2010Warsaw, Poland
22/04/2010EWEC 2010, Warsaw2 Risø DTU, Technical University of Denmark
Outline
• Motivation
• Experimental setup
• Classification of wind profiles
• Kinetic energy flux approximation
Definition of equivalent wind speed
• Power curve uncertainty
• (*) Different configurations of profile measurements
• Conclusions
22/04/2010EWEC 2010, Warsaw3 Risø DTU, Technical University of Denmark
Motivation
cf. IEC 61400-12-1 standard® only wind speed measurement at hub height
but vertical wind speed profile is relevant (!)
to be measured by (ground-based) lidar profiler
22/04/2010EWEC 2010, Warsaw4 Risø DTU, Technical University of Denmark
Experimental Setup
Preparation of lidar data
Filters:
• wind direction;
• no rain;
• lidar signal availability 100% at all heights;
• turbine status=1.
N
Experiment perfromed at Høvsøre test site, multi-MW test turbine.
22/04/2010EWEC 2010, Warsaw5 Risø DTU, Technical University of Denmark
( )fit
mfit hub
hub
zu z u
z
2( ) mfit i i
i
RSS u z u
Classification of wind profiles
RSS<0.1 ( Group 1)
RSS>0.1 ( Group 2)
22/04/2010EWEC 2010, Warsaw6 Risø DTU, Technical University of Denmark
Effect of ignoring the wind speed shearon the power performance measurement
2 different power curves for the 2 groups of profiles
22/04/2010EWEC 2010, Warsaw7 Risø DTU, Technical University of Denmark
312( ) ( ) ( )
zKE z u z C z dz
312 hub hub hubKE u A KE
312 i i i profi
KE u A KE
Kinetic energy in the wind (assuming horizontal homogeneity):
First approximation (“constant” profile):
Better approximation (measured profile):
Kinetic energy flux approximation
Wrong estimation of the kinetic energy flux because speed shear is ignored.
22/04/2010EWEC 2010, Warsaw8 Risø DTU, Technical University of Denmark
Equivalent wind speed
312
312
1/33
prof i ii
eq
ieq i
i
KE u A
U A
Awith U u
A
312
peq prof
P PC
U A KE Then
22/04/2010EWEC 2010, Warsaw9 Risø DTU, Technical University of Denmark
Using the equivalent wind speed
Same power curve for the two groups of profiles.
22/04/2010EWEC 2010, Warsaw10 Risø DTU, Technical University of Denmark
Consequence on the unified dataset
Reduction of the scatter
22/04/2010EWEC 2010, Warsaw11 Risø DTU, Technical University of Denmark
Power curve uncertainty
The equivalent wind speed method reduces the category A uncertainty.
Category B uncertainty in wind speed measurements:
- comparable to the lidar at hub height;
- higher than cup anemometer (by definition).
(Ref.: IEC 61400-12-1 / ”GUM”)
22/04/2010EWEC 2010, Warsaw12 Risø DTU, Technical University of Denmark
Power curve uncertainty
Combined uncertainty in power curve:
similar to lidar at hub height uncertainty due to shear not accounted for in the power curve as a function of hub height wind speed.
22/04/2010EWEC 2010, Warsaw13 Risø DTU, Technical University of Denmark
(*) Number and position of wind speed measurement heights
9 measurements 5 measurements 3 measurements
22/04/2010EWEC 2010, Warsaw14 Risø DTU, Technical University of Denmark
(*) Number and position of wind speed measurement heights
A significant reduction of the scatter is obtained with wind speed measurements at 3 heights.
22/04/2010EWEC 2010, Warsaw15 Risø DTU, Technical University of Denmark
(*) Number and position of wind speed measurement heights
No reduction of the scatter !
Profile extrapolation from 2 or 3 speed measurements below hub height
22/04/2010EWEC 2010, Warsaw16 Risø DTU, Technical University of Denmark
Conclusions
• There is a significant effect of ignoring the wind speed shear on power performance measurement (especially for non power law profile) – as done in IEC 61400-12-1.
• We observe a reduction of scatter with equivalent wind speed (as shear normalization procedure);
• Leading to more repeatable power curves.
• Successful experimental application of the method with a lidar.
• (*) Reduction of scatter can only be obtained with wind speed measurements at (at least) 3 measurement heights including one height above hub height.
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