Transcript Analysis of array efficiency at Horns Rev and the effect

Array efficiency at Horns Rev
and the effect of atmospheric stability
Leo E. Jensen
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Horns Rev - Layout
2
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Horns Rev – Met. masts
3
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Horns Rev – Distance from land
4
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Turbine 14 - Dimensions
5
External data - Met. masts
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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
Mast 6&7:
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
6
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Measured array efficiency
G etW FA
7
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Calculated array efficiency
G etW FA C
8
Measurement & Calculated Efficiency Comparison
Mo del ov eresti mati on (esti mated /measured)
Comparison
1.043
0.999 - 1.043
0.954 - 0.999
0.954
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G etRel
9
Wind Shear Gradients
120

100
h
Z [m]h
60
htop
hbund 40
20
0
0
2
4
6
8
10
V( h  0.01)  V( h  0.1)  V( h  0.5)  Vlog( h)
V [m/s]
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0.01

0.1

0.5
-------
80
h
h

10
12
14
Zo
0.001
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Wind Shear as function of temperature difference
11
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Wind Shear as function of temperature difference
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Choice of stability classes
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•
Tair - Twater < -0.1° : Unstable boundary layer.
• -0.1° <= Tair - Twater < 1.5° : Neutral boundary layer.
• 1.5° <= Tair - Twater
: Stable boundary layer.
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Stability classes
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Unstable Neutral Stable
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Average of all data
700 kW
425 kW
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Array Efficiency 71 %
15
Only unstable data
700 kW
450 kW
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Array Efficiency 74 %
16
Only near-neutral data
700 kW
400 kW
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Array Efficiency 66 %
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Only stable data
625 kW
275 kW
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Array Efficiency 61 %
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Distribution of stability classes
Fract io n o f t ime w it h u n stab le b ou n dary l ayer
Fract io n o f t ime w it h n eu tral b ou nd ary l ayer
Fract io n o f t ime w it h st ab le b ou nd ary l ayer
G etFract io n
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G etFract io n
G etFract io n
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Annual mean array effeiciency
Efficiency
Losses
Losses relative to all data losses
All data
90.2%
9.8%
100%
Unstable
91.5%
8.5%
87%
Neutral
88.9%
11.1%
113%
Stable
85.3%
14.7%
150%
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Conclusions
 Stability has a significant effect on array efficiency
 Stability should allways be considered when calibrating models
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 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 R&D
projects
 Pierre-Elouan Réthoré, Risø/DTU for help and inspiration on sorting and
graphical presentation of data
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 The Danish ”Public Service Obligation” (PSO) funds from Energinet.dk for
supporting the installation of the wake masts and various R&D projects on
this subject.
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