Analysis of array efficiency at Horns Rev and the effect of atmospheric stability

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Array efficiency at Horns Revand the effect of
atmospheric stability
Leo E. Jensen
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Horns Rev - Layout
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Horns Rev Met. masts
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Horns Rev Distance from land
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Turbine 14 - Dimensions
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External data - Met. masts

• Mast 67
• Wind speed
• 70 m (top)
• 60 m (nw)
• 50 m (nw/se)
• 40 m (nw)
• 30 m (nw/se)
• 20 m (nw)
• Wind direction
• 68 m
• 28 m
• Temperature
• 64 m
• 16 m
• -3 m (water)
• Air pressure
• 16 m
• Rain

• Mast 2
• Wind speed
• 62 m (top)
• 45 m (nw/se)
• 30 m (nw/se)
• 15 m (nw/se)
• Wind direction
• 60 m
• 43 m
• 28 m
• Temperature
• 55 m (x2)
• 13 m (x2)
• -4 m (water)
• Air Pressure
• 55 m
• Rain
• Humidity

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Measured array efficiency
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Calculated array efficiency
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Measurement Calculated Efficiency Comparison
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Wind Shear Gradients
Z m
V m/s
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Wind Shear as function of temperature difference
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Wind Shear as function of temperature difference
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Choice of stability classes

•  
• Tair - Twater lt -0.1 Unstable
  boundary layer.
• -0.1 lt Tair - Twater lt 1.5 Neutral
  boundary layer.
• 1.5 lt Tair - Twater Stable
  boundary layer.
•  

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Stability classes
Unstable Neutral Stable
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Average of all data
700 kW
425 kW
Array Efficiency 71
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Only unstable data
700 kW
450 kW
Array Efficiency 74
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Only near-neutral data
700 kW
400 kW
Array Efficiency 66
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Only stable data
625 kW
275 kW
Array Efficiency 61
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Distribution of stability classes
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Annual mean array effeiciency
 
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Conclusions

• Stability has a significant effect on array
  efficiency
• Stability should allways be considered when
  calibrating models
• Including stability as part of wind ressource
  assesment should be considered.

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Acknowledgements

• Sten Frandsen and Rebecca Barthelmie, Risø
  University of Edinburgh, for fruitfull
  discussions on the wake effect subject in many
  different RD projects
• Pierre-Elouan Réthoré, Risø/DTU for help and
  inspiration on sorting and graphical presentation
  of data
• The Danish Public Service Obligation (PSO)
  funds from Energinet.dk for supporting the
  installation of the wake masts and various RD
  projects on this subject.