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Field Test Results of Using a Nacelle-Mounted 

Lidar for Improving Wind Energy Capture by 

Reducing Yaw Misalignment

Paul Fleming, Andrew Scholbrock, Alan Wright

Nordic Wind Power Conference

November 4‒5, 2014

Stockholm, Sweden

NREL/PR-5000-63206
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Lidar-Enhanced Controls Research at NREL

• NREL, working collaboratively 

with research partners, has 

developed, analyzed, and field 

tested lidar-enhanced strategies 

for improving:

o Pitch control

o Torque control

o Yaw control

o Active power control.

• Several research campaigns 

ongoing

• Focus of this presentation is yaw 

control.
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Note on References

• Most of the results to follow are more fully 

described in available publications, or else 

articles under review

• Contact paul.fleming@nrel.gov to request 

references and for an explanation of slides 

and further details.
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Motivation

• Modern commercial turbines 

use active yaw control, 

typically based on 

measurements from nacellemounted wind vanes

• Static errors in measurement 

can occur as a result of:

o Rotor wake

o Complex flow from nacelle

o Environmental impacts on the 

wind vane

o Poor calibration or installation.

• Yaw misalignment can lead to 

reduced power production. Photo by Lee Jay Fingersh, NREL
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Yaw Misalignment Research Campaigns

• Campaign one:

o Learned and applied nacelle 

vane correction function

o Partnered with:

– Avent Lidar Technology

– Renewable NRG Systems (RNRG).

• Campaign two:

o Directly used lidar as control 

signal for yaw controller

o Partnered with:

– ZephIR Lidar.
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Turbine Descriptions

• Controls Advanced Research 

Turbines (CARTs) 2/3:

o Hub height of 36.6 meters 

o Rotor diameter of 42.6 meters

o Power rated at 600 kilowatts 

o Two or three blades.

• Extensively instrumented:

o Dedicated meteorological 

(met) mast

o Strain gauges

o Accelerometers.

Photo credit: Andrew Scholbrock, NREL

Photo by Lee Jay Fingersh, NREL
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Research Campaign One

• NREL/Avent/RNRG collaborated on uses of 

lidars for improved turbine control

• Phase one used the lidar measurement to 

determine yaw misalignment correction 

function running the baseline controller

• Phase two collected data with and without 

the correction function (two hours per cycle).
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Lidar Specifications

• Avent Wind Iris

o Sample rate of 2 hertz

o Pulsed lidar

o Ten measurement 

ranges

o Two horizontal beams

o Half-angle of 15o

o Calibrated to the rotor 

axis to within 0.1o.

Illustration courtesy of Samuel Davoust, Avent Lidar Technologies

Photo by Lee Jay Fingersh, NREL
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Yaw Controller Schematic
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Measurement Campaign

Figures on slides 10-13 from P. A. Fleming, A. K. Scholbrock, A. Jehu, S. Davoust, E. Osler, A. D. Wright, and A. Clifton, “Field-test 

results using a nacelle-mounted lidar for improving wind turbine power capture by reducing yaw misalignment,” in The Science 

of Making Torque from Wind, 2014, vol. 012002.

Red line indicates point when offset was computed
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• Group chose a 7.5o 

initial offset after 40 

hours of data were 

collected

• A better choice 

would have been a 

~9.5o offset if all 

data from the 

experiment had 

been used.

Yaw Error Correction
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Yaw Correction Compared to Met Mast
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Results: Power Improvement

Calculated in 10-second 

windows

Annual energy production estimated to be increased 

by 2.4% for a 7.5° offset.
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Results: Error Function

Error bars indicate 

95% confidence 

interval, points with 

large confidence 

interval not shown 

for neatness.
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Research Campaign Two

• CART3 mounted with 

ZephIR lidar

• Direct use of lidar 

signal in yaw control.

Lidar

Vane

Photo by Lee Jay Fingersh, NREL

ZephIR Lidar
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Results: Power Improvement
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Results: Error Function
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Results

• In this case, vane appeared to have had a 

fault occurring in one direction

• Rotor-induced bias toward that direction 

furthered the impact

• However, calibration with turbine offline 

appeared to have been correct

• See press release: http://www.zephirlidar.com/news/

• Paper to be presented at AIAA 2015.
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Conclusions

• Lidars have been shown to be capable of 

resolving errors in yaw calibration by:

o Learning a correction function

o Applying the lidar signal directly.
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Further Research with Yaw Control

• Ongoing research at NREL and the Delft 

University of Technology is exploring control 

strategies for wind plants

• One topic of interest is the use of yaw control 

for the redirection of turbine wakes to 

optimize overall plant power

• Accurate yaw alignment detection is a must.
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Further Research with Lidar-Enhanced Controls

• NREL has collaborated with other research 

centers and lidar manufacturers on the use of 

lidars for enhanced:

o Pitch speed control

o Torque control

o Active power controls.
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Lidar-Enhanced Pitch Control

• Several test campaigns 

completed, and several 

more ongoing

• Use lidar wind speed 

preview information as 

feedforward input to 

pitch controller

o Improve speed 

regulation

o Reduce turbine loads.

Photos by David Schlipf, Stuttgart Wind Energy (top left), 

and Lee Jay Fingersh, NREL (top right, bottom left, bottom 

right)

Stuttgart Wind Energy
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Results: Pitch Control

Rotor Speed Tower Bending

Figure courtesy David Schlipf, Stuttgart Wind 

Energy

Figure courtesy David Schlipf, Stuttgart Wind 

Energy

Photos by Lee Jay Fingersh, NREL
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Pitch Control

• Recent demonstration with Stuttgart Wind 

Energy (SWE) and a ZephIR lidar mounted on 

CART3 showed successful application of lidar 

feedforward control.

Photo credit: Lee Jay Fingersh, NREL

Photo by Lee Jay Fingersh, NREL Figure courtesy Florian Haizmann, Stuttgart Wind Energy

Stuttgart Wind Energy ZephIR Lidar
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Pitch Control

• Ongoing campaign on the 

CART2 with an Avent fivebeam demonstration lidar 

and DNV-GL is yielding 

promising results.

Photo by Jay Fingersh, NREL

Figures courtesy of Avishek Kumar and Ervin Bossanyi, DNV-GL

Avent Lidar Technology

Renewable NRG Systems DNV GL
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Active Power

• Current research in 

active power controls 

investigates the use of 

wind energy in the 

provision of grid 

services

• In study, use lidar 

measurement of wind 

speed to maintain a 

fixed power overhead

• Field test with CART3 

and Avent five-beam 

demonstration lidar.

Figure courtesy of Jake Aho, CU Boulder

Photo courtesy of Florian Haizmann

Avent Lidar Technology

Renewable NRG Systems CU Boulder
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Acknowledgments

• This work was supported by the U.S. 

Department of Energy under Contract No. 

DE-AC36-08GO28308 with the National 

Renewable Energy Laboratory. Funding for 

the work was provided by the DOE Office of 

Energy Efficiency and Renewable Energy, 

Wind and Water Power Technologies Office.
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Thanks for Your Attention!

file:///C:/Users/pfleming/Downloa

ds/25915.jpg

Photo by Dennis Schroeder, NREL

Paul Fleming | paul.fleming@nrel.gov