improvement of power curve measurement with lidar wind profiles

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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

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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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Page 1: Improvement of power curve measurement with lidar wind profiles

Improvement of power curve measurement with lidar wind profiles

R Wagner, M Courtney, J Gottschall, P Lindelöw-Marsden

EWEC 201020-23 April 2010Warsaw, Poland

Page 2: Improvement of power curve measurement with lidar wind profiles

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

Page 3: Improvement of power curve measurement with lidar wind profiles

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

Page 4: Improvement of power curve measurement with lidar wind profiles

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.

Page 5: Improvement of power curve measurement with lidar wind profiles

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)

Page 6: Improvement of power curve measurement with lidar wind profiles

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

Page 7: Improvement of power curve measurement with lidar wind 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.

Page 8: Improvement of power curve measurement with lidar wind profiles

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

Page 9: Improvement of power curve measurement with lidar wind profiles

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.

Page 10: Improvement of power curve measurement with lidar wind profiles

22/04/2010EWEC 2010, Warsaw10 Risø DTU, Technical University of Denmark

Consequence on the unified dataset

Reduction of the scatter

Page 11: Improvement of power curve measurement with lidar wind profiles

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”)

Page 12: Improvement of power curve measurement with lidar wind profiles

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.

Page 13: Improvement of power curve measurement with lidar wind profiles

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

Page 14: Improvement of power curve measurement with lidar wind profiles

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.

Page 15: Improvement of power curve measurement with lidar wind profiles

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

Page 16: Improvement of power curve measurement with lidar wind profiles

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.