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This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

Duration Test Report for the 

Ventera VT10 Wind Turbine

J. Smith, A. Huskey, D. Jager, and J. Hur

National Renewable Energy Laboratory

Technical Report

NREL/TP-5000-57142

June 2013
NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC.

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, CO 80401

303-275-3000 • www.nrel.gov

Duration Test Report for the 

Ventera VT10 Wind Turbine 

J. Smith, A. Huskey, D. Jager, and J. Hur

National Renewable Energy Laboratory

Prepared under Task No. WE11.0308

Technical Report

NREL/TP-5000-57142

June 2013
NOTICE

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Cover Photos: (left to right) photo by Pat Corkery, NREL 16416, photo from SunEdison, NREL 17423, photo by Pat Corkery, NREL 

16560, photo by Dennis Schroeder, NREL 17613, photo by Dean Armstrong, NREL 17436, photo by Pat Corkery, NREL 17721.

 Printed on paper containing at least 50% wastepaper, including 10% post consumer waste. 
1 

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at www.nrel.gov/publications.

Duration Test Report

for the

Ventera VT10 Wind Turbine

at the National Wind Technology Center 

in Boulder, Colorado

Conducted for

Wind Power Program

DOE/NREL

Conducted by

National Wind Technology Center

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, CO 80401

Joe Smith, Arlinda Huskey, Dave Jager, Jerry Hur

25 October 2012
2

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at www.nrel.gov/publications.
3

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at www.nrel.gov/publications.

Table of Contents

List of Tables.................................................................................................................................................. 4

List of Figures ................................................................................................................................................ 4

1. Background............................................................................................................................................ 5

2. Test Objective and Requirements....................................................................................................... 5

3. Description of Test Turbine.................................................................................................................. 6

4. Description of Test Site ........................................................................................................................ 9

5. Description of Instrumentation...........................................................................................................10

6. Results ...................................................................................................................................................13

6.1 Period of Testing .....................................................................................................................................13

6.2 Months of Operation................................................................................................................................13

6.3 Hours of Power Production ....................................................................................................................13

6.4 Operational Time Fraction......................................................................................................................13

6.5 Environmental Conditions ......................................................................................................................15

6.6 Dynamic Behavior ...................................................................................................................................15

6.7 Post-Test Inspection ...............................................................................................................................16

7. Uncertainty ............................................................................................................................................17

7.1 Hours of Power Production ....................................................................................................................17

7.2 Operational Time Fraction......................................................................................................................17

7.3 Environmental Conditions ......................................................................................................................17

8. Deviations and Exceptions..................................................................................................................18

8.1 Deviations from the Standard ................................................................................................................18

8.2 Deviations from Quality Assurance.......................................................................................................18

A. Appendix - Equipment Calibration Sheets........................................................................................19
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List of Tables

Table 1. VT10 Test Turbine Configuration and Operational Data.................................................................................. 8

Table 2. Equipment List for Duration Test...................................................................................................................12

Table 3. Monthly and Overall Results of the VT10 Duration Test ...............................................................................13

List of Figures

Figure 1. Ventera VT 10 test turbine at the NWTC........................................................................................................ 7

Figure 2. Electrical single-line drawing of Ventera VT10 installation ............................................................................ 9

Figure 3. Map of the test site ......................................................................................................................................10

Figure 4. Meteorological tower and instruments........................................................................................................11

Figure 5. Burned wire nut in generator slip-ring assembly .........................................................................................14

Figure 6. Power in each wind speed bin (m/s) versus time.........................................................................................15

Figure 7. Rust on the outside of the yaw bearing (circled)..........................................................................................16

Figure A.1. Primary anemometer pre-test calibration sheet; installed on 21 January 2010 and used until the end of 

the test................................................................................................................................................................20

Figure A.2. Primary anemometer post-test calibration sheet.....................................................................................21

Figure A.3. Primary anemometer pre- and post-test calibration comparison; the difference was less than 0.1 m/s 

for the range of 6 m/s to 12 m/s ........................................................................................................................22

Figure A.4. Power transducer calibration sheet; installed 28 September 2010 and used until the end of the test ...23

Figure A.5. Wind vane calibration sheet; installed 18 February 2010 and used for the entire test............................24

Figure A.6. RTD probe calibration sheet; installed 17 August 2010 and used until the end of the test......................25

Figure A.7. Pressure transducer calibration sheet; installed 17 August 2010 and used until the end of the test ......26

Figure A.8. NI 9229 data acquisition module calibration; installed 26 July 2010 and used until the end of the test . 27

Figure A.9. NI 9229 data acquisition module post-test calibration; in tolerance........................................................28

Figure A.10. NI 9217 data acquisition module calibration; installed 26 July 2010 and used until the end of the test29

Figure A.11. NI 9217 data acquisition module post-test calibration; in tolerance......................................................30

Figure A.12. NI 9205 data acquisition module calibration; installed 26 July 2010 and used until the end of the test31

Figure A.13. NI 9205 data acquisition module post-test calibration; in tolerance......................................................32
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1. Background

This test was conducted as part of the U.S. Department of Energy’s (DOE) Independent Testing project. 

This project was established to help reduce the barriers of wind energy expansion by providing 

independent testing results for small wind turbines. Five turbines were tested at the National Wind 

Technology Center (NWTC) at the National Renewable Energy Laboratory (NREL) as a part of round 

one of this project. Duration testing is one of up to five tests that may be performed on the turbines, 

including power performance, safety and function, noise, and power quality. Test results will provide 

manufacturers with reports that can be used to fulfill part of the requirements for small wind turbine 

certification.

The test equipment included a grid-connected Ventera Energy Corporation VT10 wind turbine mounted 

on an 18.3-m (60-ft) self-supporting lattice tower manufactured by Rohn. 

2. Test Objective and Requirements

The objective of this test was to assess the following aspects of the Ventera VT10 in accordance with 

Clause 9.4 of the International Electrotechnical Commission’s (IEC) standard, Wind turbines - Part 2: 

Design requirements for small wind turbines, IEC 61400-2 Ed. 2.0:2006-03 (referred to as the “Standard” 

throughout this report): 

• Structural integrity and material degradation 

• Quality of environmental protection 

• Dynamic behavior. 

The wind turbine will pass the duration test when it has achieved reliable operation for:

• Six months 

• Two thousand and five hundred hours of power production in winds of any velocity

• Two hundred and fifty hours of power production in winds of 1.2*Vave (10.2 m/s) and above

• Twenty-five hours of power production in winds of 1.8*Vave (15.3 m/s) and above.

Reliable operation means:

• Operational time fraction of at least 90%

• No major failure of the turbine or components in the turbine system

• No significant wear, corrosion, or damage to turbine components 

• No significant degradation of produced power at comparable wind speeds.

Based on the parameters defined in the Standard for small wind turbine classes, Ventera Energy 

Corporation identified the VT10 as a class III turbine. This corresponds to a Vave of 7.5 m/s.

In addition, this test was conducted in accordance with NREL quality system procedures, so that this 

report meets the full requirements of the NREL accreditation by A2LA. NREL’s quality system requires

that this report meet all applicable requirements specified by A2LA and ISO/IEC 17025 and to note any 

exceptions in the test report.
6

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3. Description of Test Turbine

The test turbine was a Ventera VT10 wind turbine. Manufactured by Ventera Energy Corporation, the 

VT10 is a downwind, three-blade, passive yaw, permanent magnet, horizontal-axis wind turbine and has 

an advertised rated power of 10 kW. The test turbine used a Diversified Technology, Inc. GALE-12 

inverter to deliver electrical energy to the 60-Hz grid. To control rotor speed, besides the inverter loading 

the generator, each blade has a tip that begins to pitch at rated rotor speed. 

Table 1 lists the configuration of the VT10 that was tested at the NWTC. Figure 1 is a picture of the VT10 

at the NWTC. 
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Figure 1. Ventera VT10 test turbine at the NWTC 

Source: NREL 22251

The system was installed in March 2010 and had several months of commissioning/shake-down, during 

which the original inverter was replaced. Additional delays in testing were from NREL personnel

incorrectly wiring a filter for the inverter and birds nesting in the lattice tower. Testing began on 19 July 

2010.
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The following components were considered part of the test turbine system:

• Generator and blades

• Tower and foundation designed for installation at the NWTC test site 3.3c

• Wind brake1

• All wiring between the generator and the utility disconnect (in the data shed)

• Inverter

• Kilowatt-hour meter. 

Table 1. VT10 Test Turbine Configuration and Operational Data

Turbine Manufacturer and Address

Ventera Energy Corporation

1302 W. 5th St

Duluth, MN 55806

Model name VT10

Production date October 2009

Generator serial number 100993

Design nominal voltage at terminals (Vac) 240 Vac

Maximum current at terminals (A) 60 A 

Design frequency at terminals (Hz) 60

Small wind turbine (SWT) class III

Vave as defined by SWT class (m/s) 7.5

Design 50-year extreme wind speed, Ve50 (m/s) 55

Rotor diameter (m) 6.7

Hub height (vertical center of rotor) (m) 21.7

Tower type

18.3-m (60-ft) Rohn SSV series, three-legged, 

self-supporting tower hinged on two legs; plus 

3-m (10-ft) extension tube for a total height of 

21.3 m (70 ft)

Rated electrical power (kW) 10

Rated wind speed (m/s) (lowest wind speed at which 

turbine produces rated power) 13

Rated rotor speed (rpm) (lowest rotor speed at which 

turbine produces rated power) 260

Rotor speed range (rpm) 100−280 (governing from 260−280)

Cut-out wind speed None

Fixed or variable pitch Fixed, but uses mechanically pitching tips to 

govern rotor speed

Number of blades 3

Blade tip pitch angle (deg) 4.5 (30° pitching range during governing)

Blade make, type, serial number

Injection-molded glass fiber plastic w/ nonlinear 

and optimized taper and twisted airfoil FX63-

137; set numbered 1408

Description of inverter

Diversified Technology, Inc.’s GALE-12

model: AMFA00100000000027AH

Serial Number: 57583

 

1 The “wind brake” is a required component supplied with the turbine. It shorts the generator’s three phases, thereby 

creating an electromagnetic force in opposition to the generator’s rotation.
9

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The VT10 turbine tested at the NWTC was in the standard configuration sold by Ventera Energy 

Corporation at that time.

Figure 2 shows the general electrical arrangement of the test. The wire run from the base of the tower to 

the meteorological (met) tower junction box was approximately 15 meters of #6 American Wire Gauge 

(AWG) wire. The wire run from the met tower junction box and wind brake to the data shed was

approximately 75 meters of #6 AWG wire. The data shed housed the inverter, instrumentation, the 

disconnect switch, and a breaker panel. The transformer was located outside and adjacent to the data shed, 

which first stepped the voltage up to 480 volts (V) and then to 13.2 kilovolts (kV) for the NREL grid.

Figure 2. Electrical single-line drawing of Ventera VT10 installation

Source: NREL, 2012

4. Description of Test Site

The test turbine was located at site 3.3c at the NWTC, which is approximately 8 km south of Boulder, 

Colorado. The terrain consists of mostly flat terrain with short vegetation. The site has prevailing winds 

bearing approximately 290° relative to true north. Figure 3 shows the turbine and met tower locations as 

well as nearby obstructions and topographical features of the site.
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Figure 3. Map of the test site

Source: NREL, 2012

5. Description of Instrumentation

Test instrumentation was installed in accordance with IEC 61400-12-1 for measuring wind speed, wind 

direction, turbine power, air temperature, and air pressure. Figure 4 provides the location of the met tower 

instruments and provides an equipment list and the specifications for each of the instruments used. For 

duration testing, there were additional signals to monitor the rotor speed and the inverter’s connection to 

the electrical grid.
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Figure 4. Meteorological tower and instruments

Source: NREL, 2012

16.7

17.1

19.0

21.2

Primary 

Anemometer

Reference

Anemometer

Wind Vane

Temperature

Pressure

VT10 hub height is 21.7 m

Heights in 

meters above 

ground level
12

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Table 2. Equipment List for Duration Test

Instrument Make and Model Serial Number Calibration Due Date

Power transducer Second Wind Phaser-5-4A 20 02061 28 September 2011

Current transformers Ohio Semitronics, 12974 001293046

001078333

Calibrated with power 

transducer

Primary anemometer Thies, First Class 0609009

21 January 2011, with 

post-test calibration on 17 

July 2011

Reference 

anemometer Met One 020 T2351 n/a

Wind vane Met One, 020C with Aluminum 

Vane G4707 18 January 2011; with in situ comparisons

Pressure sensor 

(replaced during test) Vaisala, PTB101B C1040014 10 August 2011

Temperature sensor Met One, T200 0603-1 13 August 2011

Precipitation sensor Campbell Scientific, 237 None In situ

Data acquisition 

system (DAS)

Compact DAQ w/LabView 

cDAQ backplane (9172) 12B5EBE n/a

NI 9229 13DEC38 22 February 2011

NI 9217 13FAE1C 22 February 2011

NI 9205 13E3D05 22 February 2011

The power transducers were not compliant with class 0.5 (or better) specifications of the IEC 60688, but 

they exceeded the minimum accuracy required by the Standard. This should have no effect on results or 

uncertainty. The power transducer that was used matches the performance required by the IEC Standard, 

but it is not IEC certified. Therefore, the power transducer was an exception to the Standard.

The current transformers were not compliant with class 0.5 (or better) specifications of the IEC 60044-1, 

but they exceeded the minimum accuracy required by the Standard. This should have no effect on results 

or uncertainty. The current transformers that were used match the performance required by the IEC 

Standard, but are not IEC certified. Therefore, the current transformers were an exception to the Standard.

The wind vane was slightly damaged during high winds during the final days of October 2010, but it was 

repaired on 1 November 2010. Comparisons with other wind vanes at the NWTC showed that the vane’s 

performance was consistent before and after these events. Additional comparisons showed that the 

repaired vane was consistent with a neighboring test site’s measurements until the end of the test.

However, wind direction does not factor into the duration test results; hence, detailed analysis was 

omitted from this report.

The vane calibration due date passed during the testing phase. In lieu of a recalibration or a post-test 

calibration on the vane, the aforementioned in situ comparisons were used to show that the vane’s 

performance was consistent throughout the test.

In addition, the data acquisition modules were used beyond their calibration dates. A post-test calibration 

confirmed that the modules were still operating within their design tolerances. The post-test calibrations 

can be found in Appendix A. 
13

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6. Results

6.1 Period of Testing

The testing phase for the VT10 was from 19 July 2010 to 24 May 2011.

6.2 Months of Operation

The duration test was conducted over a period of approximately 10 months. This exceeded the 6-month 

minimum required by the Standard.

6.3 Hours of Power Production

Hours of power production are divided into three categories. They include:

• Any wind speeds: 3,206.4 hours (2,500 hours required)

• Above 1.2*Vave (9 m/s): 808.8 hours (250 hours required)

• Above 1.8*Vave (13.5 m/s): 262.4 hours (25 hours required). 

Thus, the turbine met the requirements for hours of power production during the test. Table 3 shows the 

overall and month-by-month results of the duration test.

Table 3. Monthly and Overall Results of the VT10 Duration Test

 

6.4 Operational Time Fraction

The operational time fraction is defined as follows:

× %100 −−

−−− =

EUT

EUNT

TTT

TTTT O

where:

TT = total time period under consideration

TN = time during which the turbine is known to be non-operational

TU = time during which the turbine status is unknown

TE = time that is excluded in the analysis. 

Month 0 m/s 1.2*Vavg 1.8*Vavg max gust TI @ 15 m/s # points TT TG TU TE TN O [%]

Totals 3206.4 808.8 262.4 41.9 18.7 269 7539.0 6422.6 855.8 193.3 67.3 99.0

Minimum Met? Yes Yes Yes Yes Yes

Jul 2010 92 4.8 0 18.3 0 422 291.5 9.4 120.7 0 100

Aug 272.7 23.5 2.8 27.6 17.1 4 744 676.7 57.3 10 0 100

Sep 157.3 17 2.5 27.7 14.5 2 720 321.2 390.5 8.3 0 100

Oct 292.5 77.3 31.2 38.2 20.6 31 744 645.5 84.2 14.3 0 100

Nov 283 62.3 19.8 41.9 19.1 19 720 715.5 2.6 2 0 100

Dec 298.8 66.2 29.3 35.3 17.7 25 744 715.7 18.7 9.5 0 100

Jan 2011 424.8 187.2 67.3 40.9 19.3 75 744 676.8 64.1 3.2 0 100

Feb 258.8 85.2 30 32.4 17.4 41 672 478.5 186.9 6.7 0 100

Mar 398.5 101 39 40.9 19.7 34 744 637.3 38 1.3 67.3 90.4

Apr 448.5 155 37.5 40.5 17.3 34 720 699.7 3.9 16.3 0 100

May 279.5 29.3 3 30.5 20.8 4 565 564.2 0.2 1 0 100

Hours of power production Environmental conditions Operational time fraction
14

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The overall operational time fraction of the combined wind turbine system during the total testing period 

was 99.0%. The final column of Table 3 shows the operational time fraction per month. 

The total test time (TT) was 3,206.4 hours. The total environmental exposure from the beginning of the 

test to completion was over 7,539 hours.

The VT10 turbine system experienced one period of non-operational time, or downtime (TN), in March 

2011, which was due to a bad electrical connection in the up-tower slip-ring housing. On 21 March 2011, 

it was discovered that the turbine was not working properly. On 24 March 2011, inspections found that a 

wire nut had burned. See Figure 5 for details.

Figure 5. Burned wire nut in generator slip-ring assembly 

Source: NREL 22250

The main reasons for excluding time (TE) in the duration test included: 

• Time during power outages that prevented the turbine from running

• Noise or safety and function testing that required the turbine to be shut down

• NWTC-initiated inspections of the VT10. 

If no reliable measurements were available, the time was classified as unknown time (TU) because the 

turbine’s status was unknown. These downtimes occurred primarily when the data acquisition system 

(DAS) was off (during maintenance or a power outage), or if both of the anemometers were iced.
15

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6.5 Environmental Conditions

During the test period, the highest instantaneous wind speed was 42 m/s during November 2010. The 

average turbulence intensity at 15 m/s during the test was 18.8%.

Figure 6. Power in each wind speed bin (m/s) versus time

For the power degradation analysis, the average power level for each wind speed bin was plotted as a 

function of time over the whole test period. This plot was analyzed for any noticeable trends in power 

production (shown in Figure 6). There is a slight increase in several bins during the winter months, which 

corresponds to increased air density. After accounting for seasonal density changes, there did not appear 

to be a trend of decreased power at any given wind speeds over time.

6.6 Dynamic Behavior

The turbine operation was observed by NWTC personnel for at least 5 minutes at wind speeds of 

approximately 5 m/s, 10 m/s, 15 m/s, and 20 m/s, for a total observation time of at least 1 hour. 

The VT10 requires winds between 5 and 6 m/s to get the rotor spinning, but winds as low as 3 m/s can 

keep a spinning rotor moving. The turbine at NWTC, when not spinning, could exhibit significant yaw 

error in winds below 4 m/s, but in winds above 4 m/s, it would orient itself properly in the downwind 

orientation. It was never observed to operate in the upwind position.

0

1

2

3

4

5

6

7

8

9

10

Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May

Power (kW)

Month

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26
16

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In winds around 10 m/s, the turbine tracked the wind well when compared to the wind vane on the nearby 

met tower. Some tower vibration was observed, but it was not excessive (accelerations on the VT10 were 

not measured).

In winds above 13 m/s, the rotor tips would start to pitch. This would dramatically increase the noise, but 

the turbine continued to track the wind well. There were noticeable vibrations in the tower, especially at 

the joint between the lattice tower and the 3-m extension tube, where the generator was mounted. These 

were not deemed excessive.

6.7 Post-Test Inspection

The test was completed on 24 May 2011. The turbine was decommissioned on 13 June 2011. Post-test 

inspections took place at decommissioning and a more thorough inspection was performed on 16 June

2011. The following post-test inspection observations were made:

• There was no significant accumulation of wear during the test. However, neither the generator nor 

the blades were disassembled, as their disassembly could be dangerous (strong magnets in the 

generator and springs with potential energy in the blades), and without proper reassembly, the 

VT10 would be unusable for a future installation.

• During installation very minor cracks were noticed in the generator’s housing, which was a resin 

cast around the stator coils. These cracks did not appear to expand at all during the test.

• The exterior of the yaw bearings were rusting, but this would not affect performance in any way.

• The nut and bolt positions were marked before the test, and all were still in the same positions at 

the end of the test.

Figure 7. Rust on the outside of the yaw bearing (circled) 

Source: NREL 22254
17

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7. Uncertainty

The uncertainty was estimated for the following parameters:

• Hours of power production 

• Operational time fraction

• Environmental conditions. 

No uncertainty analysis was done for the power degradation results. These results were used only to find 

relative trends that might indicate deterioration of the turbine’s performance. 

7.1 Hours of Power Production

It is assumed that the turbine is producing power for the entire 10-minute period whenever the average 

power for that period is positive. This method overestimates time for power production in low average

wind speed, when the VT10 might only produce for a fraction of the 10-minute period. At higher wind 

speeds, this method would produce less of an overestimate. If the VT10 was only producing power 25%

of the time in average wind speeds below 5 m/s, the total time of power production would be 2,550 hours, 

which is still in excess of the minimum required by the Standard.

For the hours of power production above 9 m/s and 13.5 m/s, the uncertainty in the wind speed is 

assumed to be the dominant factor. Assuming an uncertainty in wind speed of 0.3 m/s, the hours of power 

production reduced to 804.3 (above 9.3 m/s) and 260.8 (above 13.8 m/s), which is still well in excess of 

the 250 and 25 hours, respectively, that are required.

The analysis tool used at the NWTC does not accurately account for switching from standard to daylight 

savings time, even though the time stamp on the data does reflect this switch. It is assumed that the net 

effect on results is negligible, even though its influence can be seen in the values of TU for November and 

March.

7.2 Operational Time Fraction

If there was a failure at any time during a 10-minute period, the entire 10-minute period was classified as 

downtime (TN). This means that the 99.0% is the lower bound of the operational time fraction.

7.3 Environmental Conditions

The maximum deviation in wind speed measurements for the calibration range was 0.028 m/s, which 

resulted in a standard uncertainty of 0.02 m/s. The calibration range was only to 16 m/s, and thus an 

extrapolation to 44 m/s could be unreliable. However, it was assumed that the standard uncertainty of 

calibration was consistent at 0.02 m/s. Combining the calibration uncertainty with operational 

characteristics (0.052 m/s + 0.52%), mounting effects (1%), and terrain effects (2%), while assuming that 

the DAS uncertainty was negligible (for the maximum instantaneous gust of 42 m/s) the uncertainty was 

1 m/s. 

Standard deviation of wind speed was used for the turbulence intensity (TI) calculation. Average wind 

speed at 15 m/s has an uncertainty of 0.4 m/s, resulting in a TI estimate of between 18.3% and 19.3%.
18

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8. Deviations and Exceptions

8.1 Deviations from the Standard

As explained in Section 5, Description of Instrumentation:

• The power transducer was not compliant with IEC 60688, but exceeded the minimum accuracy 

required by the Standard. This should have no effect on results or uncertainty.

• The current transformers were not IEC 60044-1, but exceeded the minimum accuracy required by 

the Standard. This should have no effect on results or uncertainty.

8.2 Deviations from Quality Assurance

The primary anemometer was used beyond its calibration due date. The anemometer was post-test 

calibrated and found to have held its calibrations for the test period. Appendix A includes the post-test 

calibration sheets.

The wind vane was damaged and repaired during the test. It was also used beyond its calibration due date.

In situ comparisons with other NWTC test sites showed that the vane held its performance throughout the 

test.

The DAS modules were used beyond the calibration due date. They were post-test calibrated and found to 

be in compliance with the specifications. Appendix A includes the post-test calibration sheets.
19

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

A. Appendix - Equipment Calibration Sheets

A.1. Primary anemometer pre-test calibration sheet; installed on 21 January 2010, 

and used until the end of the test 

A.2. Primary anemometer post-test calibration sheet

A.3. Primary anemometer pre- and post-test calibration comparison; the difference 

was less than 0.1 m/s for the range of 6 m/s to 12 m/s

A.4. Power transducer calibration sheet; installed 28 September 2010, and used until 

the end of the test

A.5. Wind vane calibration sheet; installed 18 February 2010 and used for the entire 

test

A.6. RTD probe calibration sheet; installed 17 August 2010 and used until the end of

the test

A.7. Pressure transducer calibration sheet; installed 17 August 2010 and used until

the end of the test

A.8. NI 9229 data acquisition module calibration; installed 26 July 2010 and used until 

the end of the test

A.9. NI 9229 data acquisition module post-test calibration; in tolerance

A.10. NI 9217 data acquisition module calibration; installed 26 July 2010 and used until 

the end of the test

A.11. NI 9217 data acquisition module post-test calibration; in tolerance

A.12. NI 9205 data acquisition module calibration; installed 26 July 2010 and used until

the end of the test

A.13. NI 9205 data acquisition module post-test calibration; in tolerance
20

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Figure A.1. Primary anemometer pre-test calibration sheet; installed on 21 January 2010

and used until the end of the test
21

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Figure A.2. Primary anemometer post-test calibration sheet
22

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Figure A.3. Primary anemometer pre- and post-test calibration comparison; the 

difference was less than 0.1 m/s for the range of 6 m/s to 12 m/s

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

5

6

7

8

9

10

11

12

13

110 130 150 170 190 210 230 250

Wind Speed [m/s]

Difference [m/s]

Anemometer Pulses [Hz]

Primary Anemometer Pre- & Post-Test Calibrations

pre-test

post-test

difference
23

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Figure A.4. Power transducer calibration sheet; installed 28 September 2010 and used 

until the end of the test
24

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Figure A.5. Wind vane calibration sheet; installed 18 February 2010 and used for the 

entire test
25

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Figure A.6. RTD probe calibration sheet; installed 17 August 2010 and used until the end 

of the test
26

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Figure A.7. Pressure transducer calibration sheet; installed 17 August 2010 and used 

until the end of the test
27

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Figure A.8. NI 9229 data acquisition module calibration; installed 26 July 2010 and used 

until the end of the test
28

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Figure A.9. NI 9229 data acquisition module post-test calibration; in tolerance
29

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Figure A.10. NI 9217 data acquisition module calibration; installed 26 July 2010 and used 

until the end of the test
30

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Figure A.11. NI 9217 data acquisition module post-test calibration; in tolerance
31

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Figure A.12. NI 9205 data acquisition module calibration; installed 26 July 2010 and used 

until the end of the test
32

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Figure A.13. NI 9205 data acquisition module post-test calibration; in tolerance