A Case Study on Using a Nacelle Lidar for Power Performance Testing in Complex Terrain Megan Quick

December 11, 2013

Introduction

• Can a nacelle lidar be used for site calibration?

• Can nacelle lidar be used for power performance testing in complex terrain?

• Previous investigation for uses in simple terrain was done by DTU

• New draft standard includes provisions for ground based lidar

• Case study of available data

• Opportunistic approach at existing test site

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Nacelle Lidar – Avent Wind Iris

• Avent Wind Iris

• Two-beam, pulsed laser

• 10 measurements between 80 m and 440 m upwind

• Lidar availability is mainly limited by blade pass

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Site Layout

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• Moderately sloping complex hillside terrain

• Wind Iris mounted on top of 80-m hub height (HH) wind turbine (WTG)

• First class anemometer mounted at 80-m HH

• Height of lidar measurement varies with terrain

Terrain profile looking North & uphill

200 m measurement circle Terrain profile looking East & across hill

Wind Iris Wind Speed (WS) and Turbulence Intensity (TI) Measurements

• Original scalar lidar output: poor agreement with met mast

• Post processed vector lidar output: lidar WS & TI have better agreement

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Verification

• Verified as per Annex L of Draft IEC 12-1 Ed.2

• Wind speed is binned per 0.5 m/s wind speed bins

• Deviation = (𝑉𝑀𝑒𝑡 − 𝑉𝐿𝑖𝑑𝑎𝑟)/𝑉𝑀𝑒𝑡

• Deviations should be < 1%

• Deviations are large for WS < 7 m/s

• Blades block measurement

• Filters to adjust:

• Availability

• Rotor RPM

• Filters improve correlation

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Filters: turbine ON, no curtailment, lidar availability > 20%, valid sector 80°- 90°

Verification with Elevation Difference

• Removed data with low rotor RPM

• Only used data with lidar facing uphill

• Met wind speed 2.5% higher than lidar

• Indicates the decreased measurement height

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Filters: turbine ON, no curtailment, lidar availability > 20%, valid sector 30°- 60°

Site Calibration • Can site calibration be replaced by a nacelle lidar?

• Calculated lidar-based site calibration correction factors

• Met with 𝑆𝐶𝐼𝐸𝐶 𝑀𝑒𝑡

• Met with 𝑆𝐶𝑙𝑖𝑑𝑎𝑟

• Does not consider wind evolution between 80 m upwind and the turbine rotor

• WTG must be OFF

𝑆𝐶𝑙𝑖𝑑𝑎𝑟 =𝑙𝑖𝑑𝑎𝑟80

𝑙𝑖𝑑𝑎𝑟200

𝑆𝐶𝐼𝐸𝐶𝑚𝑒𝑡 =𝑀𝑒𝑡𝑡𝑢𝑟

𝑀𝑒𝑡𝑟𝑒𝑓

𝑙𝑖𝑑𝑎𝑟200 𝑙𝑖𝑑𝑎𝑟80

𝑀𝑒𝑡𝑡𝑢𝑟 𝑀𝑒𝑡𝑟𝑒𝑓

Proposed

lidar site cal

IEC met

site cal

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Results – Correction Factors – Flat Sector

• Lidar correction factor

• Limited data due to WTG Availability

• Site Calibration without turbine mast

• 𝑆𝐶𝐼𝐸𝐶𝑚𝑒𝑡 - 𝑆𝐶𝑙𝑖𝑑𝑎𝑟 < 0.1 m/s across WS range

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IEC Compliant Site Calibration

Lidar 200 m – 80m Site Calibration

Results – Correction Factors –Power Curve

• Well within the uncertainty for each measurement.

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Power Curves with Corrections – 80°-90° sector

• Lidar only used to develop the correction factor

• Applied to Met Wind speed

• 8 m/s Rayleigh distribution annual energy production (AEP) lidar site calibration is 0.56% lower than AEP

Filters: turbine ON, no curtailment, lidar availability > 20%, valid sector 80°- 90°

Results – Correction Factors- 60°-90° Sector

10° Sector

Center (°)

Measurement

Height (m)

𝑆𝐶𝐼𝐸𝐶𝑚𝑒𝑡 - 𝑆𝐶𝑙𝑖𝑑𝑎𝑟

4m/s (m/s) 8m/s (m/s) 12m/s (m/s)

65 70 0.21 0.11 0.01

75 75 -0.04 -0.03 -0.02

85 80 -0.02 -0.04 -0.05

WTG

North & Uphill

• Site calibration factors for 3 sectors

• Two flattest sectors match IEC site calibration

• 65° sector has significant deviation from IEC site calibration

• Low data counts introduces extra uncertainty

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Results – Correction Factors – Power Curve

• With a 8 m/s Rayleigh distribution AEP is 0.6% higher with the site calibration factors calculated from the Lidar

• Well within the uncertainty for each measurement.

• AEP difference between only using the 80°-90° sector and 60°-90° is about 1%

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Power Curves with Corrections 60°-90°

Filters: turbine ON, no curtailment, lidar availability > 20%, valid sector 60°- 90°

Results – Power Curves

• Three scenarios for comparison

• IEC Compliant Test with met mast and site calibration

• Nacelle Anemometer comparison without any adjustment

• 200m Lidar with lidar correction factor applied calibration

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• The difference in %AEP for an 8 m/s Rayleigh wind distribution is:

• (AEPIEC – AEPLidar200

)/ AEPIEC = 0.1%

• (AEPIEC – AEPNacAne

)/ AEPIEC = 0.1%

Filters: turbine ON, no curtailment, lidar availability > 20%, valid sector 60°- 90°

Conclusions

• Results are encouraging and nacelle lidar may have uses in complex terrain

• Not yet suitable to replace IEC compliant site calibration and power curve measurements – but promising for locations with little elevation change within 2D

• Upcoming IEC-61400-12-1 update only includes ground-based lidar – operational assessment

• Further studies at other sites are needed to prove the results

• Additional shear measurement points would allow for REWS evaluation

• Results Summary:

• Updated vector calculation shows better correlation with met mast

• Verification shows good correlation at high wind speeds and filters were found that correlate at low wind

• Calibration factors with Lidar and IEC method were similar

• Resulting power curves were very similar

• No significant conclusions could be made due to lack of data

• Different measurement methods were compared significant differences were seen in the power curves but the AEP results were similar. Favorable AEP results may be due to the flat terrain

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Question Slide Place holder

When will lidar overtake met masts for power performance testing?

A. 5 years

B. 10 years

C. Never

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Thank you!

• References: • Wagner, R: Courtney, M; Gottschall, Antoniou, I; Møller, R; Pederson, Sm; Velociter, T; Bardon, M;

Le, N; Mouritzen, AS; 2012 “Power performance measurement using a nacelle lidar”

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