challenges in modelling offshore wind – how to address them using observation
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Challenges in modelling offshore wind – how to address them using observation. Idar Barstad [email protected]. Improvements of resource estimates and forecast of energy yield rely primarily on the quality of numerical models and their input data. - PowerPoint PPT PresentationTRANSCRIPT
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Challenges in modelling offshore wind – how to address them using observation
Idar Barstad
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Improvements of resource estimates and forecast of energy yield rely primarily on the quality of numerical models and their input data.
There are many ways to set up the model suite, and the numerical model tool is normally tailored for generic use.
The system can sometimes be inherently unpredictable
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Future wind power potential in Europe
Barstad et al. (2012), J. Renewable Energy
- Arpege/Ifs T159L60c3-- (1972-2001) N/F--(2020-2049) – R[1-4] (A1B)
SST = ERA40 + delta from CGCMs(variability from ERA40=>get more realistic sea ice)
[ Barstad et al. (2008), Clim.Dyn. ]
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Current wind climateWind speed at 100m ::Annual average (1972-2001)
Solid line=8.5 m/s
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Future power potential(2020-2049)
Fractional power potential in reference to (1972-2001)
Black line=1.0
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Example 12UTC 29Feb 2008
The effect of surface waves
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WRF roughness length (m) after 12 h
Colour scale for roughness length / m Colour scale for roughness length difference / m
No coupling Two-way coupling Difference
Work by: Alastair Jenkins, Alok Gupta, John Michalakes (NREL), Idar Barstad
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The effect on U10 (wind speed) in WRF
2-way coupling :: Significant impact on the wind field!
After 12 hrs simulation
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High resolution downscaling (9-3km)
0
2
-2
BIAS (Obs-ERAI)
BIAS (Obs-3km)
BIAS (Obs-9km)
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High resolution downscaling (9-3km)
Qscatassimilation
STD
0
2
-2
Coastal effects
RMSE
BIAS
Stations along the Norwegian Coast
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(Courtesy M Zagar, Vestas
BIAS
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Inversion - Vosper’s regime diagramWeak inversion
Vosper (2004)
Strong inversion
Strong inversion
Hm/PBLH
Valentia Irland
- 6700 cases over 10 yrs (2000-2010)
- Conditions for lee waves
15-20% of the time
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Drag from turbines in a single cell, distributed over several layers
- > works on both the TKE and the momentum eqs.
(Blahak et al. 2010)
Wind turbine drag in WRF from V3.3
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Fitch et al. (2012); MWR
Q:
How sensitive is the power output to the atmospheric characteristics?
Simulation of a wind farm100 x 5MW
wind turbines
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Generation of pressure gradients by wind farmGeneration of pressure gradients by wind farm::- θ increases with height under typical stable conditions- θ increases with height under typical stable conditions- As air lifted over farm, lower θ air brought up from below- As air lifted over farm, lower θ air brought up from below- This creates cold anomaly aloft and thus high pressure anomaly below - This creates cold anomaly aloft and thus high pressure anomaly below – –> pressure gradients deflect wind.> pressure gradients deflect wind.
Slide 3
top viewtop view
side viewside view
Typical θ-profile over sea: Typical θ-profile over sea:
The principle:
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Slide 11
Full model• WRF 1 km model• Ideal set-up• turbine drag 5MW
top view
Idealized study –sensitivity to upstream parameters
Work by: Fitch and Barstad
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(9km-3km-1km)
Demonstration of the WRF-turbine dragat Dogger bank
15 x15 km with a 5 MW turbine in each grid cell
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1km domainwind and wind speed
1km domainwind, wind speed &
vorticity
Dogger bank wind farm
Conclusions: - 10% effect on wind speed(up to 60% on power)- Long wakes
(15 x15 km with a 5 MW turbine in each grid cell)
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40km
20km
Reduced model –”single farm”Same model as in Smith (2009)
Fra
ctio
nal w
ind
redu
ctio
n
-50 0 50
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Reduced model – “single farm”
The effect of the inversion strength
double inversion strength
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Two farms – reduced model
Present in all runs (Lx=10km)
Second farm (Lx=10km)
Utop=15 m/sUBL=8.5 m/sH=500mdth/th=0.01
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Two farms – reduced model
Present in all runs (Lx=10km)
Second farm (Lx=10km)
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Conclusions• Models may produce data, but we have to be
critical to their results
• Models may be tailored to your specific needs -> talk to an expert!
• Observational campaigns should be design to address scientific questions. Do we have these questions?
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NOAA / MODIS 23 MAR 2010, Aleutians Islands
Thank you for your attention!
Alaska