© Fraunhofer IWES

COMPARISON OF A PULSED DOPPLER LiDAR WITH A 200 M MET MAST IN

COMPLEX TERRAIN

Tobias Klaas1, Doron Callies1 Christoph Langenmayr1,Lukas Pauscher1, Saskia Hagemann1, Zouhair Khadiri-Yazami1, Bernhard Lange1 (1) Fraunhofer IWES, Kassel, Germany

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Outline

Measurement site at Rödeser Berg Site description, measurement campaign, data basis

LiDAR measurements in complex terrain Performance of LiDAR vs. mast measurements

Correction with WAsP Engineering and Meteodyn WT Predicted bias compared to measured difference

Virtual met mast Conclusion and Outlook

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Project „Utilization of Inland Wind Power“

Source: RP Kassel, 2012Source: Die Auswärtige Presse, 2011

Complex Terrain

Forest

New onshore windturbines

Mesoscale modelling

Project duration 2012 – 2014 Wind characteristics, LiDAR measurements, onshore wind energy

potential

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Measurement location in central Germany

Source: Google Earth

measurement site

Wind measurements in complex terrain at Rödeser Berg Typical wind farm location in central / south Germany

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Mast layout and specifications

200 m wind measurement mast in complex forested terrain

IEC conform booms with 5,40 m length, orthogonal to main wind direction

13 measurement heights

Co-located LiDAR measurements with LEOSPHERE Windcube WLS7 V1

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Measurement campaign and data processingMast - LiDAR comparison Measurement period: 21 Jan – 30 June 2012 Periods of icing were removed by visual comparison of heated

vs. unheated cups Invalid and/or physically unreasonable values were removed Measurements are compared at 120, 160 and 200 m

Mean wind profile Scatter plots and linear regression Diurnal pattern Directional dependence of bias

Due to terrain complexity and wind LiDAR measurement principle we expect significant bias.

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LiDAR availability with height

More than 80% of measured valuesin 10 minute averaging interval must be available

Periods of rain were removed

Availability decreases with height:

85 % at 135m 60 % at 200m

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LiDAR vs. mast measurements:Mean wind profile

Mean profile fits well, LiDAR shows small underestimation Strong effects from forest and terrain below 60m height

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LiDAR vs. mast measurements:scatter plot at 120 m and 200 m

Compared to flat terrain (Hovsøre) the scatter is significantly higher

Source: Gottschall, Courtney 2010

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LiDAR vs. mast measurements:Diurnal variation at different heights

Significant diurnal pattern at all heights Deviations between mast and LiDAR increase during nighttime

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LiDAR vs. mast measurements:Directional dependence at 120 m

only wind speeds > 4m s-1

Mean bias approx. between -4% and +2%

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only wind speeds > 4m s-1

LiDAR vs. mast measurements:Directional dependence at 120 m

Positive deviation for flow along the ridge

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LiDAR vs. mast measurements:Directional dependence at 120 m

Significant underestimation in main wind direction

only wind speeds > 4m s-1

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LiDAR vs. mast measurements:Directional dependence with height

Lightning rod

only wind speeds > 4m s-1

Shape and mean bias similar for all heights Height dependency of about 1%, depending on sector

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LiDAR correction with flow simulation LiDAR measurement bias is

mainly caused by flow inhomogeneity

Flow simulation can be used to assess the wind conditions and develop correction methods WAsP Engineering with

Bingöl‘s correction script Meteodyn WT and LiDAR

correction module

measurement site

main w

ind

dir.

Source: Bingöl 2009

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Comparison of different correction algorithms to measured bias

WEng estimation is much too high, but the pattern is reproduced Bias estimated by Meteodyn WT fits much better, but is slightly too

low

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Correction with Meteodyn WT:Predicted bias for three heights

Less symmetry in estimation due to CFD simulation Height-dependency of bias for certain sectors

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Three Windcube v1 LiDARs mounted on maneuverable tilting platforms

Focusing of the three laser beams on one point

Automatically measuring heights from 40m to 200m

Results were compared to the 200m mast at Rödeser Berg

Realization of a virtual met mast using three Pulsed Doppler LiDARs

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Conclusions

LiDAR shows error in complex terrain: Patterns follow orography, effects are site specific Deviation follows same pattern at all heights (up to 200m!) Deviations approx. between -4% and +2% Compensating effects in mean wind profile Deviations during night time

Meteodyn and WEng correction: Shape of predicted bias fits (fairly) well for both tools Bias predicted by WEng is much too high Very good reproduction of bias by Meteodyn WT

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Outlook

Detailed evaluation of flow models at complex site with mast data Different stabilities Different forest/roughness parameterization

LiDAR vs. Mast in complex terrain at several other complex sites More complex sites, more forested sites

Evaluation of different CFD-tools for LiDAR correction Meteodyn WT / WindSim / WEng / OpenFoam

3D-LiDAR experiments Detailed comparison of virtual vs. real met. mast

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M. Sc. Tobias KlaasTobias.Klaas@iwes.fraunhofer.de

Fraunhofer Institute for Wind Energy and Energy System Technology IWES Königstor 59, 34119 Kassel, Germany

Thank you for your attentionVisit us at stand B-B77!Do not miss our related posters and presentations: Pauscher, Lukas:

Wind over complex, forested terrain: First year of measurement with 200m research mastTuesday, 5 February 2013 , Room: LEHAR 2-4 , 11:00 - 12:30 Wind Resources - Moving the barriers (part 1) 

Khadiri-Yazami, Zouhair: The realization of a Virtual met mast based on three Doppler wind LiDAR, Poster No. 404