Chris Slinger, Matthew Leak, Mark Pitter, Michael Harris

ZephIR Ltd, Ledbury, Herefordshire, HR8 1EU, UK

Relative power curve measurements using turbine

mounted, continuous-wave lidar

04 February, 20132

Power curve measurements for turbinesPower curves important for measuring turbine performance

IEC Standard 61400-12-1 describes measurement procedures for absolute power curves

– Require hub height measurement of free stream wind incident on the turbine (2D upwind of turbine)

– Current standard requires hub height metmast– New, draft standard IEC 61400-12-1 CD

• Ground based lidar supplemented by short metmast• Concept of rotor equivalent wind speeds

Relative power curves– Broader range of measurement techniques applicable– Measurements can be made in the blade induction

zone– Allow comparison of turbine performance pre- and

post- intervention/adjustment/maintenance– Can quantify relative performance improvements

Rotor equivalent wind speed concept.

Graphic credit:I. Antoniou

04 February, 20133

Advantages in using turbine mounted lidar for power curve measurements

Measurement of wind incident on turbine irrespective of wind direction

Low cost and convenient compared to metmast– Rapid deployment (½ day)– On- and off-shore– Long life, low maintenance

Measurements at multiple rangesCircular scanned lidars permit measurement of a variety of wind field quantities around rotor disk

– Hub height and rotor averaged horizontal wind speeds

– Wind yaw alignment relative to turbine– Vertical wind shear– Wind veer (variation of wind direction with height)– TI and other turbulence measures– Wind field complexity– Turbine wakes and effects of complex terrain– Horizontal shear and inflow angle ZephIR turbine wake

visualisation example

04 February, 20134

Operating principles of a CW scanning lidar †

Continuous wave (CW) lidar beam focussed at user set range(s) upstream of the turbine

– 10 m to 300 m ranges

Measure Doppler shift of light backscattered from aerosols

Circular scan in plane of the rotor– 1 scan per second– 50 readings per scan

LOS readings combined with a wind model to yieldwind field measurements

Advantages of CW lidar include– High sensitivity in all atmospheres– Fast sample and integration times (20 ms)– Sensitivity independent of range– Short range of operation possible (down to 10 m)– Class 1 eye safe operation

Pulsed lidars are an alternative for longer ranges† ZephIR 300 parameters

04 February, 20135

Example results from a turbine mounted trial

04 February, 20136

Trial descriptionAim

– To demonstrate and quantify turbineperformance improvements after turbine tuning

NEG-Micon turbine, 2 MW, 72 m rotor ØFlat terrain, Eastern JutlandNacelle roof mounted, dual mode, ZephIR 300 CW lidarRanges R of 10m, 30m, 50m, 100m and 180m (i.e. 2.5 Ø)Trial organised by ROMO Wind

First part of trial (03 January to 15 March)– Unoptimised turbine

Second part of trial (15 March to 5 April)– Reoptimised turbine

Photo credit:ROMO Wind

04 February, 20137

Example of data measured, 10 minute averagedZephIR lidar 10 m range dataUnfiltered scatter plot shown (includes turbine shut down events)

}500 kW generator

2 MW generator

04 February, 20138

1000 2000 3000 4000 5000 6000 7000

5

10

15

Yaw misalignment detectionYaw error of 14°to 16°evident in CW lidar yaw alignment measurementsRemedied by nacelle wind vane recalibrationEffects clearly visible in ZephIR measured power curves pre- and post- yaw recalibrationROMO Wind estimated improved AEP of ~5% after yaw recalibration

0 2 4 6 8 10 12 14 16 180

500000

1000000

1500000

2000000

2500000

Pre 15/03/2012 Post 15/03/2012

Wind speed measured by ZephIR at a range of 180m /ms-1

Turb

ine

pow

er o

utpu

t (W

)

All power curves in this presentation are hub height (HH), corrected for air density, as specified in IEC 61400-12-1 Error bars shown are for standard uncertainty

Mea

sure

d ya

w m

isal

ignm

ent /

Time

15m

arch

2012

Turb

ine

yaw

reca

libra

ted

After turbine yaw recalibration

Before turbine yaw recalibration

04 February, 20139

6 8 10 12 14 16

500 000

1 .0 106

1 .5 106

2 .0 106Low shear , high shear

Wind shear and turbulence effectsPlots of HH powercurves filtered for high and low vertical wind shear(with inset of shear statistical distribution)

Plots of HH powercurves filtered for high and low TI (with inset of TI statistical distribution)

6 8 10 12 14 16

500 000

1.0 10 6

1.5 10 6

2.0 10 6Low T I, high T I

Wind speed measured by ZephIR at a range of 180m /ms-1

Turb

ine

pow

er o

utpu

t /W

Wind speed measured by ZephIR at a range of 10m /ms-1

Turb

ine

pow

er o

utpu

t /W

• Shear and TI determined from lidar measurements• Results consistent with other hub height power curve studies Measurement of shear, TI, and veer is important for accurate power curve determination

04 February, 201310

Measurement of blade induction effectsBlade induction effects slow wind speed as wind approaches the blades

1000 2000 3000 4000 5000 6000Time

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8

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W indspeed m s 1W indsp eeds measured at different lidar ranges

180m

100m

50m

30m

10m

Lidar scan ranges

Windspeed /ms-1

Time /10 min intervals

04 February, 201311

Measurement of blade induction effectsEffect clearly visible in relative power curves derived at different rangesMeasurement scatter increases slightly with range

Unfiltered multi-range scatter (left, with turbine manufacturer’s power curve) and binned power curves (right)from a nacelle-mounted ZephIR. 25 days data, post wind vane recalibration.

Ranges

Turbine power /WTurbine power /W

Wind speed /ms-1

Wind speed /ms-1

First known lidar measurement of close-in blade induction effects

04 February, 201312

Practical lessons learned from turbine mounted lidar trials Lidar must be small enough to fit through turbine hatches and turbine internal spaces

– < 0.55 m x 0.55 m cross sectionLidar must be of low enough mass for easy 2 man deployment

– < 40 kgMounting system must be safe to use, and capable of being used on a variety of nacelle roofs

– Adjustable carbon fibre tripod frameOn-lidar aids for alignment with turbine axis are important if lidar is to be used for turbine yaw optimisation

– Visible laser projection systemMeasurements must be made at ±2½ % of hub height (±1 % in new draft standard)

– Electronics levels with real time readout and loggingFlow across full rotor needed for accurate turbine performance determination

– Ability to measure vertical shear, TI, veer and rotor equivalent wind speeds

04 February, 201313

Other applications of turbine mounted lidarsTurbine control Example study results DEL = damage equivalent load

DEL reductions as a function of wind speed

Lifetime DEL reduction (tower base loads)

Significant potential for turbine load reduction using turbine mounted lidar

Maximum advantages will be accrued using turbines designed to incorporate fully lidar systems

Reduced energy generation costs

“Both pulsed and continuous-wave LIDAR types are suitable, as long as they can sample something like 10 points distributed around the swept area every second or so and provide a few seconds of lookahead time.” †

Experimental verification of benefits of lidar controlled turbines is still underway

† ”Wind turbine control applications of turbine-mounted LIDAR”, Bossanyi et al, DEWEK

2012 Graphics credit: Bossanyi et al, Garrad Hassan

04 February, 201314

Power curves with CW lidar: conclusionsA ZephIR CW lidar has been used to identify, verify and quantify improvement in turbine performanceRelative and absolute turbine power curves were determinedYaw misalignment, wind shear and TI were measured and have a significant effect on hub height power curvesBlade induction effects and their impact on relative power curves were measured

CW scanned lidars will allow further improvements in power curve measurement statistics

– Use of rotor averaged wind quantities– Wind veer effects

Longer term CW lidar developments promise much for turbine control applications

New dual-mode ZephIR CW lidar, undergoing final tests in Denmark

04 February, 201315

Thank you for your attention

Chris SlingerZephir Ltdchris.slinger@zephirlidar.com+44 1531 650 757

For further information, please contact

The authors would like to acknowledge the cooperation and assistance of ROMO Wind A/Swww.romowind.com

Acknowledgements

Monday @ 5 pmStand A-D40, Natural Power / Zephir

New, turbine optimised , ZephIR DM launch

04 February, 201316

From measurements to wind quantification(1) Fitting a wind model to multiple measurements

Least-squares fit (LSF) of a wind model applied to measured LOS speeds

Standard outputs are horizontal wind speed, vertical shear and yaw alignment

– Wind speeds at any height across the rotor disk. Excellent basis for rotor-equivalent wind speeds

Secondary outputs include quantification of flow complexity and TI

Extraction of other wind quantities possible e.g. inflow, horizontal shear

Benefits of the above approach include aggregated analysis of complex wind flow conditions

04 February, 201317

From measurements to wind quantification(2) pairwise algorithms

Pairs of LOS values, e.g. from each scan at hub height, are used to determine horizontal wind speed and yaw misalignment

– No direct output of wind shear. Indirect output by considering multiple pairs.Can be extended to determine wind veerWell suited to hub and rotor equivalent wind speeds and veerReal time tilt/roll measurement ensures LOS always available at specified heights

Pairwise algorithm chooses slice using logged tip-tilt angles to ensure hub height wind speed measurements with high availability

Wind veer example,(also showing turbine blades, prior to

blade filtering)