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Making.torque.2012 October 9-11, 2012. Oldenburg; Kurt S. Hansen. 2. DTU Wind Energy, Technical University of Denmark. Outline. 1. Motivation;. 2.
Wind turbine wakes

Park power deficit in due to atmospheric stability Kurt S. Hansen DTU Wind Energy [email protected]

Dr. Rebecca J. Barthelmie Indiana Univ., USA Søren Ott & Gunner Larsen; DTU Wind Energy

DTU Wind Energy Department of Wind Energy

Outline 1. Motivation; 2. Classification of stratification; 3. Power deficit along row of wind turbines; 4. Park power polar; 5. Park efficiency; 6. Conclusion; 7. Acknowledgement & references.

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DTU Wind Energy, Technical University of Denmark

Making.torque.2012 October 9-11, 2012 Oldenburg; Kurt S. Hansen

Motivation Grouping two or more wind turbines results in a loss of energy production when the turbines operate [partly] in the wake of each other. Wake deficit highly depends on: •Spacing; •Wind speed; •Turbulence; •Stratification;

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DTU Wind Energy, Technical University of Denmark

Making.torque.2012 October 9-11, 2012 Oldenburg; Kurt S. Hansen

Determination of offshore stratification • Theory: Monin – Obukhov MO-length L:

1/L = (g  *)/(  Ts u*2)

Characteristic temperature:

*=-‚’w’Ú/u*

Friction velocity:

u* =‚-u’w’Ú½

AMOK is a tool for analysing of offshore met data Input: < Tair > < Twater >

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DTU Wind Energy, Technical University of Denmark

Making.torque.2012 October 9-11, 2012 Oldenburg; Kurt S. Hansen

Classification of stratification

Horns Rev- sectorwise atmospherie stability; 7 - 9 m/s (AMOK)

PDF - %

100%

80%

vs

60%

s ns n nu u

40%

vu

20%

0%

0

5

30

60

DTU Wind Energy, Technical University of Denmark

90

120

150 180 210 Flow sector - deg.

240

270

300

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Making.torque.2012 October 9-11, 2012 Oldenburg; Kurt S. Hansen

Offshore stratification classification Turbulence intensity - bin averaged as function of wind speed for each stability class. Example based on Horns Rev measurements recorded on a 62 m offshore mast.

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DTU Wind Energy, Technical University of Denmark

Making.torque.2012 October 9-11, 2012 Oldenburg; Kurt S. Hansen

Example: Horns Rev offshore wind farm: 80 x 2 MW, D=80m

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DTU Wind Energy, Technical University of Denmark

Making.torque.2012 October 9-11, 2012 Oldenburg; Kurt S. Hansen

Example of power deficit along wind turbine rows with 7D internal spacing.

Narrow inflow sector = 5 deg

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DTU Wind Energy, Technical University of Denmark

Making.torque.2012 October 9-11, 2012 Oldenburg; Kurt S. Hansen

Quantification of power deficit – caused by stratification • Extract power deficit for 0 – 360° All observations - reference Stable stratification (vs,s) Neutral stratification (ns,n,nu) Unstable stratification (u,vu)

• Demostration wind farm: Horns Rev (80x2 MW) • Results for wind speed 8±1 m/s • Reference wind speed ≈ ”free” wind turbines ~ 100%

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DTU Wind Energy, Technical University of Denmark

Making.torque.2012 October 9-11, 2012 Oldenburg; Kurt S. Hansen

Quantification of power deficit – caused by stratification Reference power

7D spacing

9.4 & 10.4D

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DTU Wind Energy, Technical University of Denmark

Making.torque.2012 October 9-11, 2012 Oldenburg; Kurt S. Hansen

Park efficiency (η): Reference ηi = AEP160MW/80*AEP2MW ; for vi=4±0.5, 5±0.5,..24±0.5 m/s power, 100%

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DTU Wind Energy, Technical University of Denmark

Making.torque.2012 October 9-11, 2012 Oldenburg; Kurt S. Hansen

Park efficiency

4 ≤ Uhub ≤ 24 m/s All recordings Unstable (vu-s) Neutral (nu-n-ns) Stable (s - vs) Weighted

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DTU Wind Energy, Technical University of Denmark

Park efficiency 90% 92% 91% 89% 90%

Making.torque.2012 October 9-11, 2012 Oldenburg; Kurt S. Hansen

Conclusion • Robust classification of stratification; • Power deficit along wind turbines; • Park polar for 0 – 360 degree inflow; • Park efficiency estimation; • Estimated park efficiency varies up ±2% due to stability effects;

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DTU Wind Energy, Technical University of Denmark

Making.torque.2012 October 9-11, 2012 Oldenburg; Kurt S. Hansen

Acknowledgement The research has been performed in part by EUDP 640100462 which is funded by the Danish Energy Agency.

We acknowledge Vattenfall AB and DONG Energy A/S for using the SCADA data from the Horns Rev offshore wind farm. Reference: The impact of turbulence intensity and atmospheric stability on power deficits due to wind turbine wakes at Horns Rev wind farm, by Kurt S. Hansen et al.;we.512 (2012), Wiley

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DTU Wind Energy, Technical University of Denmark

Making.torque.2012 October 9-11, 2012 Oldenburg; Kurt S. Hansen