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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 2010 20-23 April 2010 Warsaw, Poland. Outline. Motivation Experimental setup Classification of wind profiles Kinetic energy flux approximation

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Improvement of power curve measurement with lidar wind profiles

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  1. 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

  2. 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

  3. 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

  4. Experimental Setup Experiment perfromed at Høvsøre test site, multi-MW test turbine. N • Preparation of lidar data •  Filters: • wind direction; • no rain; • lidar signal availability 100% at all heights; • turbine status=1.

  5. Classification of wind profiles RSS<0.1 ( Group 1) RSS>0.1 ( Group 2)

  6. Effect of ignoring the wind speed shearon the power performance measurement  2 different power curves for the 2 groups of profiles

  7. Kinetic energy flux approximation Kinetic energy in the wind (assuming horizontal homogeneity): First approximation (“constant” profile): Better approximation (measured profile):  Wrong estimation of the kinetic energy flux because speed shear is ignored.

  8. Equivalent wind speed Then

  9. Using the equivalent wind speed  Same power curve for the two groups of profiles.

  10. Consequence on the unified dataset  Reduction of the scatter

  11. Power curve uncertainty (Ref.: IEC 61400-12-1 / ”GUM”) 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).

  12. 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.

  13. (*) Number and position of wind speed measurement heights 3 measurements 5 measurements 9 measurements

  14. (*) Number and position of wind speed measurement heights A significant reduction of the scatter is obtained with wind speed measurements at 3 heights.

  15. (*) Number and position of wind speed measurement heights Profile extrapolation from 2 or 3 speed measurements below hub height No reduction of the scatter !

  16. 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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