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Measuring offshore winds from onshore – one lidar or two?
Vasiljevic, Nikola; Courtney, Michael; Peña, Alfredo; Lea, Guillaume; Vignaroli, Andrea
Publication date:2015
Link back to DTU Orbit
Citation (APA):Vasiljevic, N. (Author), Courtney, M. (Author), Peña, A. (Author), Lea, G. (Author), & Vignaroli, A. (Author).(2015). Measuring offshore winds from onshore – one lidar or two?. Sound/Visual production (digital), EuropeanWind Energy Association (EWEA).
https://orbit.dtu.dk/en/publications/acdc96aa-5a9a-453d-989b-487f0dab6906
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Measuring offshore winds from onshore – one lidar or two?
Nikola Vasiljević, Michael Courtney, Alfredo Peña, Guillaume Lea and Andrea Vignaroli
11/03/2015
EWEA Offshore 2015, Copenhagen
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DTU Wind Energy, Technical University of Denmark
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Estimation of near-shore wind resource
EWEA OFFSHORE 2015 2
Land Sea
Area of future wind farm
Technique Pros Cons
Mesoscale models Cheap Uncertainty of prediction up to 10%
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DTU Wind Energy, Technical University of Denmark
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Estimation of near-shore wind resource
EWEA OFFSHORE 2015 3
Land Sea
Area of future wind farm
Measurements
Technique Pros Cons
Mesoscale models Cheap Uncertainty of prediction up to 10%
Mesoscale models + local measurements
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DTU Wind Energy, Technical University of Denmark
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Estimation of near-shore wind resource
EWEA OFFSHORE 2015 4
Land Sea
Area of future wind farm
Technique Pros Cons
Mesoscale models Cheap Uncertainty of prediction up to 10%
Mesoscale models + local measurements
Uncertainty reduced to 3%
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DTU Wind Energy, Technical University of Denmark
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Options for local measurements
EWEA OFFSHORE 2015 5
Land Sea
Area of future wind farm
Met mast
Technique Pros Cons
Mesoscale models Cheap Uncertainty of prediction up to 10%
Mesoscale models + local measurements
Uncertainty reduced to 3%
Floating lidar
Scanning lidar
Scanning lidar
Scanning lidar
Lidar
Met mast
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DTU Wind Energy, Technical University of Denmark
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Which measurement solution is most cost-effective (cost vs. accuracy)?
EWEA OFFSHORE 2015 6
Land Sea
Area of future wind farm
Met mast
Technique Pros Cons
Mesoscale models Cheap Uncertainty of prediction up to 10%
Mesoscale models + local measurements
Uncertainty reduced to 3% $$$?
Floating lidar Scanning lidar
Scanning lidar
Scanning lidar
Lidar
Met mast
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DTU Wind Energy, Technical University of Denmark
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Which measurement solution is most cost-effective?
• The RUNE project is designed to investigate cost-effective measurement solutions for improving wind resource modeling of coastal areas.
EWEA OFFSHORE 2015
Onshore lidar Offshore mast Floating lidar Onshore scanning lidar(s)
Comparison with mast mounted cup anemometer and wind vane
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DTU Wind Energy, Technical University of Denmark
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First attempt to answer the question: One or two lidars?
EWEA OFFSHORE 2015 8
Land Sea
Area of future wind farm
Met mast
Scanning lidar
Scanning lidar
Scanning lidar
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DTU Wind Energy, Technical University of Denmark
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Lidar measurement background
EWEA OFFSHORE 2015
Wind
Vwind
Vwind
Lidar
A lidar can only measure a portion of the wind vector!!!
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DTU Wind Energy, Technical University of Denmark
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Dual-Doppler
EWEA OFFSHORE 2015
Vwind
Two independent LOS measurements Low elevation angles => neglect vertical component With two lidars it is possible to measure: - Horizontal wind speed - Wind direction
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DTU Wind Energy, Technical University of Denmark
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Conical scan
EWEA OFFSHORE 2015
Vwind
Flow horizontally homogenous Conical scan (VAD) => estimate wind vector
φ
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Sector scan
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DTU Wind Energy, Technical University of Denmark
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Sector scan
EWEA OFFSHORE 2015
Vwind
φ
θn θ1
θ2
Flow horizontally homogenous Vertical component low Low elevation angle Sector scan => estimate horizontal wind speed and wind direction
θ1 θ2
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Neglect vertical component
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DTU Wind Energy, Technical University of Denmark
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Pre-RUNE experiment, April-May 2014
EWEA OFFSHORE 2015 13
D e n m a r k Høvsøre
N
S
E W
1000 m
Long-range WindScanners
Risø
Master computer
A detailed description of the long-range WindScanners: Nikola Vasiljevic. A time-space synchronization of coherent Doppler scanning lidars for 3D measurements of wind fields. PhD thesis, Technical University of Denmark (DTU), 2014. PhD-0027 Link: http://bit.ly/1K82w0G
EWEA
http://bit.ly/1K82w0G
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DTU Wind Energy, Technical University of Denmark
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Experimental layout
EWEA OFFSHORE 2015 14
N
S
E W
250 m
Mast
WindScanner 1
WindScanner 2
WindScanner 3
60˚
Configuration
WindScanner 1 Fixed line-of-sight (LOS) 2.5 Hz measurement rate Probe length 60 m (FWHM) Dual-Doppler
WindScanner 2 Fixed line-of-sight (LOS) 2.5 Hz measurement rate Probe length 60 m (FWHM) Dual-Doppler
WindScanner 3 60˚ sector scan 2.5 Hz measurement rate Probe length 60 m (FWHM) 12 s per complete scan 30 LOS per scan Backward/Forward
116 m
110 m
5.85 ˚
WindScanner 1
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DTU Wind Energy, Technical University of Denmark
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Data processing
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Horizontal wind speeds from 4 to 25 m/s
165 h
Wake free sector (118˚-270˚)
143 h
Hard target removal
47 h
Run at least 10 min Signal quality (-27dB
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DTU Wind Energy, Technical University of Denmark
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Horizontal wind speed
EWEA OFFSHORE 2015 16
Cup anemometer Two lidars (Dual-Doppler) One lidar (Sector Scan 60˚)
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DTU Wind Energy, Technical University of Denmark
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Horizontal wind speed
EWEA OFFSHORE 2015 17
One lidar (Sector Scan 60˚) Two lidars (Dual-Doppler)
Cup One lidar Two lidars
Number of samples 140 140 140
Mean wind speed [m/s] 7.07 7.04 7.04
R2 / 0.98 0.99
Difference [m/s] / 0.03 0.03
Difference [ %] /
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DTU Wind Energy, Technical University of Denmark
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EWEA OFFSHORE 2015 18
Wind vane Two lidars (Dual-Doppler) One lidar (Sector Scan 60˚)
Wind direction
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DTU Wind Energy, Technical University of Denmark
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Wind direction
EWEA OFFSHORE 2015 19
One lidar (Sector Scan 60˚) Two lidars (Dual-Doppler)
Cup One lidar Two lidars
Number of samples 140 140 140
Mean wind direction [ ˚] 168.40 171.75 169.50
R2 / 0.97 0.99
Difference [ ˚] / -2.11 -1.11
Difference [ %] / 1.98 0.65
Standard deviation of the difference [ ˚] / 4.04 1.92
dif dif
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DTU Wind Energy, Technical University of Denmark
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One lidar or two?
• One lidar will provide necessary local measurements
• If you have sufficient funds there are merits of using two lidars: - Higher measurement rate - Small portion of area sampled - More measurement points - If the flow is not horizontally homogeneous
• Be careful with the installation! A high pointing accuracy is crucial in achieving reliable measurements!!!
EWEA OFFSHORE 2015 20
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DTU Wind Energy, Technical University of Denmark
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Future work
• Derive a parameter that indicates if the estimated values of the horizontal wind speed and direction from the sector scan are trustworthy
• Relating the theoretical calculation of the minimum sector scan to the experimental results
• Perform a similar experiment in real offshore conditions while going for a longer range and adding: - floating lidar - onshore lidar - …
• Test pointing accuracy
EWEA OFFSHORE 2015 21
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DTU Wind Energy, Technical University of Denmark
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EWEA OFFSHORE 2015
For a live demonstration of the long-range WindScanner system visit the DTU WIND ENERGY stand in front of the Bella Center!
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DTU Wind Energy, Technical University of Denmark
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EWEA OFFSHORE 2015
Thank you!