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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

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

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%





Land Sea


Measurements

Technique Pros Cons


Mesoscale models + local measurements





Land Sea


Technique Pros Cons



Uncertainty reduced to 3%



Options for local measurements


Land Sea


Met mast

Technique Pros Cons



Uncertainty reduced to 3%

Floating lidar

Scanning lidar

Scanning lidar

Scanning lidar

Lidar

Met mast



Which measurement solution is most cost-effective (cost vs. accuracy)?


Land Sea


Met mast

Technique Pros Cons



Uncertainty reduced to 3% $$$?

Floating lidar Scanning lidar

Scanning lidar

Scanning lidar

Lidar

Met mast



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

7



First attempt to answer the question: One or two lidars?


Land Sea


Met mast

Scanning lidar

Scanning lidar

Scanning lidar



Lidar measurement background

EWEA OFFSHORE 2015

Wind

Vwind

Vwind

Lidar

A lidar can only measure a portion of the wind vector!!!

9



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

10



Conical scan

EWEA OFFSHORE 2015

Vwind

Flow horizontally homogenous Conical scan (VAD) => estimate wind vector

φ

11

Sector scan



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

12

Neglect vertical component



Pre-RUNE experiment, April-May 2014


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



Experimental layout


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



Data processing

15

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



Horizontal wind speed


Cup anemometer Two lidars (Dual-Doppler) One lidar (Sector Scan 60˚)



Horizontal wind speed


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 [ %] /




Wind vane Two lidars (Dual-Doppler) One lidar (Sector Scan 60˚)

Wind direction



Wind direction


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



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!!!




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

For a live demonstration of the long-range WindScanner system visit the DTU WIND ENERGY stand in front of the Bella Center!



EWEA OFFSHORE 2015

Thank you!

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Measuring offshore winds from onshore – one lidar or two? · Downloaded from orbit.dtu.dk on: Feb 01, 2021 Measuring offshore winds from onshore – one lidar or two? Vasiljevic,