Evaluation of wind turbine performance using WINDCUBE with FCR™

and WIND IRIS nacelle-mounted LiDARs in complex terrainThomas Burchhart1, C Gray2, Raghu Krishnamurthy3, Matthieu Boquet3

1 VERBUND Hydro Power GmbH, Austria / 2 Uptime Engineering, Germany / 3 LEOSPHERE SAS, France

The measurements from all the three devices were used for calculating the power curve of the Enercon 7.5 MW wind turbine. The high frequency 1 second data was used to

measure the Turbulence Intensity from the Wind Iris measurements and the WINDCUBE V2. The comparison between the

WINDCUBE V2 with FCR and Wind Iris measurements is shown in Figure 4. The good comparison in the sector, where both the

devices overlap is shown (270 – 290°). The R² between the measurements is 98.5%, which provides confidence in the measurements

obtained for the campaign.

The power curve from each of the measurements is shown in Figure 5. This shows small variations in between the measurements

compared to the guranteed power curve. The difference between the measurements is shown in Table 1. The highest mean wind

Speed is measured by the nacelle anemometer. The WINDCUBE + FCR shows the smallest variability compared to the WTG.

References

Conclusions

Complex Terrain Campaign Setup

Motivation:

The purpose of the campaign was to accurately estimate the power curve

performance of a 7.5 MW wind turbine by Enercon. The measurements were

directed towards capturing various wind regimes, in particular Turbulence Intensity

(TI) estimates and their effect on the performance of the turbine. To this effect, two

remote sensing devices were deployed. A nacelle-mounted Lidar (Wind Iris) and a

vertical profiler (WINDCUBE V2) 2.5 D away from the turbine location (maintaining

the IEC 61400-12-1 guidelines). Due to the complexity of the terrain, the

WINDCUBE V2 was equipped with Flow Complexity Recognition (FCR) software.

This allowed accurate estimates of wind speed and direction from WINDCUBE V2

device.

Based on IEC 61400-12-Ed.2 standard requirements, remote sensing devices have been proven to be used as a standard for power curve measurements in simple terrain. Large rotor

diameter, multi MW turbines in complex terrain face completely new challenges in measuring the inhomogeneous incoming wind field across the rotor swept area using remote

sensing devices. To this effect a measurement campaign was carried out using both, a ground based WINDCUBE with Flow Complexity Recognition (FCR™) software, and nacelle

mounted Wind Iris on top of a 7.5 MW turbine. During the three month measurement campaign ten minute average data and one hertz real-time data were recorded with both LiDARs

and the turbine SCADA as well. The effect of rotor equivalent wind speed measured by WINDCUBE FCR™ and hub-height winds as measured by both WINDCUBE FCR™ and Wind

Iris will be presented. A detailed variance analysis of the power curve with respec t to wind veer, shear, turbulence intensity and wake effects of neighboring turbines is performed. The

effect of nacelle transfer function is observed to be significant on performance of turbines at higher wind speed. This study would provide new insights into the flow around turbines

using one hertz real-time data of remote sensing instruments.

1. All the devices compare reasonable well amongst each other.

2. The WTG PC correlates less closely with WEC power in Complex terrain,

3. NTF investigation showed that the nacelle anemometer power curves would tend to overestimate the power curve, especially above 12m/s,

4. Day time and night time comparison show significant variability in various wind regimes.

The overall conclusion is that a multi-range turbine mounted LiDAR is a serious and competitive tool to investigate wind turbine performance in complex terrain, by providing a wide

number of answers and a simplified and cheaper set-up.

Abstract

WINDCUBE FCR Performance

[1] Wagner R, Pedersen TF, Courtney M, Antoniou I, Davoust S, Rivera RL. Power curve measurement with a nacelle mounted LiDAR. DTU Wind Energy, 2013.

[2] Krishnamurthy R, M Boquet, FCR performance and uncertainty evaluation., EWEA Annual Event, 2014.

Orientation of

WindCube V2

Beams

N

Power Curve Assessment with Wind Iris & WINDCUBE FCR

1. Analysis and

comparison of radial

wind of all LOS gates

2. Characterization and

classification of the

wind complexity

3. Calculation of the

final wind speed value

Figure 1. The remote sensing device installation at

the complex terrain test site.

The WINDCUBE V2 was equipped with FCR software, and the

performance of the FCR software in similar terrain conditions

compared to a mast is shown below. The FCR software is

intended to assess the flow complexity, with the help of the 5th

vertical beam. The measurements from all the beams along with

the 5th beam provide necessary information about the flow

inhomogeinity on the volume of the vertical profiler and accurate

estimates in inhomogenous flow conditions can be produced.

The measurements in Figure 3,

show comparison of the WINDCUBE

V2 to an IEC met-mast in moderately

Complex terrain. The vertical profiles

at each given wind direction is shown.

The good comparison between the

Met-mast and FCR measurements

show the unique performance of the

FCR software in similar terrain

conditions. For further validation of

FCR measurements please refer to

Krishnamurthy et al., 2014.

Figure 2. The Flow Complexity

Recognition software basics.

Figure 3. WINDCUBE V2 + FCR compared to a met-mast in complex terrain..

0 2 4 6 8 10 12 14 160

2

4

6

8

10

12

14

16

WindCube + FCR Wind Speed (ms-1

)

Win

dIr

is W

ind

sp

eed

(m

s-1)

y = 0.997X

R2 = 98.46%

Mean Diff. (µ) = 0.03 ms-1

Std Diff. () = 0.32 ms-1

# Data = 723

Wind Speed [270 - 290°]

Linear Fit [Y = MX]

Device WindSpeed [m/s] Deviation [%]

WTG 7.259 100

WindIris 7.106 -2.104

WindCube 7.211 -0.665

WindCube FCR 7.237 -0.305

The TI from day and night time and their

corresponding power curves are shown in Figure

5. The day time generally corresponds to high TI

measurements while the night time corresponds

to low TI measurements. Significant variability

can be observed betwenn the two times of the

day. The night TI was 37% lower compared to

the day time TI for the current site.

Hence the performance of the measurements

could significantly impact the measurements due

to various reasons:

1. Incorrect Control,

2. Incorrect NTF calculation,

3. High Shear conditions.

Figure 4. Comparison between

Wind Iris and WINDCUBE V2 +

FCR

Figure 5. High (Left) and low (right) TI power cuves comparison measurements from the Wind Iris measurements.

Figure 4: Power curve assessed by each instrument.

Table 1. Wind speed deviations between instruments.

PO.025

EWEA Resource Assessment 2015 – Helsinki– 2-3 June 2015