Technical Report

NREL/TP-500-46192

December 2009

Wind Turbine Generator System 

Power Performance Test Report 

for the Mariah Windspire 1-kW

Wind Turbine

A. Huskey, A. Bowen, and D. Jager
Wind Turbine Generator System

Power Performance Test Report

for the

Mariah Windspire 1-kW Wind Turbine

Conducted for

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401

Conducted by

National Wind Technology Center

National Renewable Energy Laboratory

1617 Cole Boulevard

Golden, Colorado 80401

Arlinda Huskey, Amy Bowen, Dave Jager

10 June 2009
ii

Notice

This report was prepared by the National Renewable Energy Laboratory (NREL), operated for 

the United States Department of Energy (DOE) by the Alliance for Sustainable Energy, LLC 

(Alliance), as an account of work sponsored by the United States government. The test results 

documented in this report define the characteristics of the test article as configured and under 

the conditions tested.

THIS REPORT IS PROVIDED "AS IS" AND NEITHER THE GOVERNMENT, ALLIANCE, NREL 

NOR ANY OF THEIR EMPLOYEES, MAKES ANY WARRANTY, EXPRESS OR IMPLIED, 

INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 

PURPOSE, OR ASSUMES ANY LEGAL LIABILITY OR RESPONSIBILITY FOR THE 

ACCURACY, COMPLETENESS, OR USEFULNESS OF ANY SUCH INFORMATION DISCLOSED 

IN THE REPORT, OR OF ANY APPARATUS, PRODUCT, OR PROCESS DISCLOSED, OR 

REPRESENTS THAT ITS USE WOULD NOT INFRINGE PRIVATELY OWNED RIGHTS. 

Neither Alliance nor the U. S. Government shall be liable for special, consequential or incidental 

damages. Reference herein to any specific commercial product, process, or service by trade 

name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its 

endorsement, recommendation, or favoring by the United States government or any agency 

thereof. The views and opinions of the authors expressed herein do not necessarily state or 

reflect those of the United States government or any agency thereof or Alliance. 

NREL is a DOE Laboratory, and as an adjunct of the United States government, cannot certify 

wind turbines. The information in this report is limited to NREL’s knowledge and understanding 

as of this date. 

NREL is accredited by the American Association for Laboratory Accreditation (A2LA) and the 

results shown in this test report have been determined in accordance with the NREL’s terms of 

accreditation unless stated otherwise in the report.

This report shall not be reproduced, except in full, without the written approval of Alliance or 

successor operator of NREL.

Approval By: __________________________________________________________

Arlinda Huskey, NREL Test Engineer Date

Review By: ___________________________________________________________

Jeroen van Dam, NREL Test Engineer Date
iii

Contents

Contents............................................................................................................................................................iii

List of Tables......................................................................................................................................................iv

List of Figures......................................................................................................................................................v

1. Background ............................................................................................................................................... 1

2. Test Summary............................................................................................................................................ 1

3. Test Turbine Configuration......................................................................................................................... 4

4. Test Site Description .................................................................................................................................. 6

5. Description of Test Equipment................................................................................................................... 8

6. Description of Test Procedure ...................................................................................................................10

7. Test Results ..............................................................................................................................................11

7.1. Results of Power Performance Test for the Normal Configuration..............................................................11

7.1.1. Tabular Results for Normal Power Production ....................................................................................11

7.1.2. Graphical Results for Normal Power Production.................................................................................15

7.2. Results of Power Performance Test for Optimized Power Production.........................................................21

7.2.1. Tabular Results for Optimized Power Production ...............................................................................21

7.2.2. Graphical Results for Power-Optimized Configuration........................................................................25

8. Deviations and Exceptions ........................................................................................................................32

8.1. Deviations from the Standard......................................................................................................................32

8.2. Exceptions to NWTC-CT Quality Assurance System .....................................................................................32

A. Appendix – Pictures of the Test Site from the Turbine Base .......................................................................33

B. Appendix – Equipment Calibration Sheets.................................................................................................38
iv

List of Tables

Table 1. Test Turbine Configuration .............................................................................................4

Table 2. Structures close to the test turbine .................................................................................7

Table 3. Criteria for test site without site calibration .....................................................................7

Table 4. Equipment used in the power performance test .............................................................8

Table 5. Uncertainty values used in the analysis........................................................................10

Table 6. Performance at Sea-level air density; 1.225 kg/m3 for normal power production..........12

Table 7. Performance at site average density; 1.00 kg/m3 for normal power production............13

Table 8. Annual energy production (AEP) at sea-level density; 1.225 kg/m3 for normal power 

production .......................................................................................................................14

Table 9. Annual energy production at site average density; 1.00 kg/m3 for normal power 

production .......................................................................................................................14

Table 10. Performance at sea-level air density; 1.225 kg/m3 for optimized power production....22

Table 11. Performance at site average density; 0.95 kg/m3 for optimized power production .....23

Table 12. Annual energy production (AEP) at sea-level density; 1.225 kg/m3 for optimized power 

production .......................................................................................................................24

Table 13. Annual energy production at site average density; 0.95 kg/m3 for optimized power 

production .......................................................................................................................24
v 

List of Figures

Figure 1. Power curve summary for the normal configuration ...................................................... 2

Figure 2. Power curve summary for the power optimized configuration ....................................... 3

Figure 3. Mariah Power Windspire 1-kW test turbine at the NWTC .............................................. 5

Figure 4. Map of the test site ........................................................................................................ 6

Figure 5. Meteorological tower and instruments ........................................................................... 9

Figure 6. Power curve at sea-level density; 1.225 kg/m3 for normal power production ............... 15

Figure 7. Power curve at site average density; 1.00 kg/m3 for normal power production ........... 16

Figure 8. Scatter plot of mean, standard deviation, minimum, and maximum power data for 

normal power production .............................................................................................. 17

Figure 9. Coefficient of power at sea-level density; 1.225 kg/m3 for normal power production ... 18

Figure 10. Wind turbulence intensity as a function of wind speed during for normal power 

production .................................................................................................................... 19

Figure 11. Wind speed and turbulence intensity as a function of wind direction during test for 

normal power production .............................................................................................. 20

Figure 12. Rotor speed as a function of wind speed (1-minute averages) and binned values for 

normal power production .............................................................................................. 21

Figure 13. Power curve at sea-level density; 1.225 kg/m3

 for optimized power production ........ 25

Figure 14. Power curve at site average density; 0.95 kg/m3

 for optimized power production ..... 26

Figure 15. Scatter plot of mean, standard deviation, minimum, and maximum power data for 

optimized power production ......................................................................................... 27

Figure 16. Coefficient of power at sea level density; 1.225 kg/m3 for optimized power 

production .................................................................................................................... 28

Figure 17. Wind turbulence intensity as a function of wind speed during the test for optimized 

power production .......................................................................................................... 29

Figure 18. Wind speed and turbulence intensity as a function of wind direction during the test for 

optimized power production ......................................................................................... 30

Figure 19. Rotor speed as a function of wind speed (1-minute averages) and binned values for 

optimized power production ......................................................................................... 31
1

1. Background

This test is being 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 turbines. In total, four turbines are 

being tested at the National Wind Technology Center (NWTC) as a part of this project. Power 

performance testing is one of up to 5 tests that may be performed on the turbines, including 

duration, safety and function, noise, and power quality tests. 

2. Test Summary

Figure 1 is a summary of the results of a power performance test that NREL conducted on the 

Mariah Windspire 1-kW wind turbine. In this test, the Windspire turbine was installed at the 

NWTC, close to Boulder, Colorado. This test was conducted in accordance with the 

International Electrotechnical Commission’s (IEC) standard, Wind Turbine Generator Systems 

Part 12: Power Performance Measurements of Electricity Producing Wind Turbines, IEC 61400-

12-1 Ed.1.0, 2005-12. However, because the Windspire is a small turbine as defined by IEC, 

NREL also followed Annex H that applies to small wind turbines. This test report refers to these 

procedures as the Standard.

During this test, two configurations were tested on the same turbine. In the first configuration, 

the turbine inverter was optimized for power production. Data collection was not completed with 

the last required wind speed bin (14 m/s) not filled. In the second configuration, the turbine 

inverter was set for normal power production. Again, data collection was not completed with the 

last wind speed bin (14 m/s) not filled. In both configurations, the inverter experienced failures 

and the tests were not finished.

In Figure 1, the first summary result, the normal configuration results are shown. Power is 

normalized to sea-level air density. Additional results are given in Section 7.1. This test was 

begun on October 7, 2008, and was ended on November 19, 2009. 291.57 hours of valid data 

were collected during that time. The highest wind speed bin filled was the 13.5 m/s bin. The 

amount of test data is not sufficient to meet the requirements of the Standard, Annex H.

In Figure 2, the second summary result, the optimized power configuration results are shown. 

is normalized to sea-level air density. Additional results are given in Section 7.2.

This test was begun on June 12, 2008, and was ended on September 13, 2009. 1023.5 hours

of valid data were collected during that time. The highest wind speed bin filled was the 13.5 m/s 

bin. The amount of test data is not sufficient to meet the requirements of the Standard, Annex H.

Power
2

Figure 1. Power curve summary for the normal configuration

Power Performance Test Bin Wind Bin Number

Mariah Power Windspire Speed Power Data Cp

(m/s) (kW) Points

Sea-Level Density Power Curve 0.54 -0.01 477 -10.70

1.03 -0.01 905 -1.56

Report Created: 1.52 -0.01 1,595 -0.48

2.01 -0.01 2,228 -0.21

Turbine Specifications: 2.50 -0.01 2,343 -0.11

2.99 -0.01 2,084 -0.06

Serial Number: 800021 3.48 0.00 1,335 -0.02

Rated Power: 1 kW 3.98 0.01 910 0.02

Cut-in Wind Speed: 4.00 m/s 4.50 0.03 670 0.07

Cut-out Wind Speed: N/A 4.99 0.05 599 0.10

Rated Wind Speed: 11 m/s 5.49 0.09 567 0.11

Rotor Diameter: 3.076 m 6.00 0.13 573 0.13

6.50 0.18 510 0.14

Control Type: Stall 7.01 0.25 472 0.16

Pitch Setting: Fixed 7.49 0.32 409 0.17

7.98 0.41 351 0.18

8.50 0.52 291 0.19

Site Conditions: 8.99 0.64 307 0.19

9.49 0.76 253 0.20

Location NWTC, Boulder, CO 9.98 0.88 189 0.19

Average Air Density: 1.00 kg/m3 10.48 0.96 132 0.18

Measurement Sectors: 132 - 323 degrees true 10.99 1.02 114 0.17

11.48 1.06 65 0.15

11.99 1.09 42 0.14

Test Statistics: 12.49 0.99 38 0.11

13.02 0.96 21 0.10

Start Date: 13.47 0.99 14 0.09

End Date:

Amount of Data Collected: 291.57 hours

Highest Bin Filled: 13.50 m/s

Test Completed? No

October 7, 2008

November 19, 2008

January 23, 2009

Sea-Level Air Density Normalized Power Curve

Mariah Power Windspire

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10 12 14

Wind Speed, m/s

Normalized Power, kW

0.00

0.05

0.10

0.15

0.20

0.25 Cp

Power

Cp
3

Figure 2. Power curve summary for the power optimized configuration
4

3. Test Turbine Configuration

Table 1 lists the configuration of the Windspire that was tested at the NWTC. 

Table 1. Test Turbine Configuration

Turbine make, model, serial number, production year Mariah Power, Windspire, 800021, 2008

Horizontal or vertical axis turbine Vertical

Rotor diameter (m) 3.05

Rotor height (m) 6.10

Rotor center height (m) 6.10

Tower type Tubular

Rated electrical power (kW) 1

Rated wind speed (m/s) 11.0

Rotor speed range (rpm) 0 – 500

Fixed or variable pitch Fixed

Number of blades/airfoils 3

Blade pitch angle (deg) 0

Blade make, type, serial number Mariah Power, Airfoil

Description of control system (device & software 

version)

Windspire 1.2G

The rotor diameter was verified by measurements. 
5

Figure 3. Mariah Power Windspire 1-kW test turbine at the NWTC
6

4. Test Site Description

The test turbine is located at site 3.3C at the NWTC, located 8 miles south of Boulder, Colorado. 

The terrain primarily consists of mostly flat terrain with short vegetation. The test site has 

prevailing wind bearing at 292 degrees relative to true north. For measurements where it is 

important to accurately measure wind speed, NREL used data obtained when wind direction is 

between 132° and 323° degrees true. In this measurement sector, the influence of terrain and 

obstructions on the anemometer is small. Figure 4 shows the turbine and meteorological tower 

locations. This figure also shows nearby obstructions and topographical features of the site. 

Sizes and distances of nearby obstructions are provided in Table 2. 

Figure 4. Map of the test site
7

Table 2. Structures close to the test turbine

Designation

Bearing from

Test Turbine

(deg. T)

Distance from

Test Turbine

(m)

Obstruction

Height

(m)

Rotor Diameter 

or Obstruction

Width

(m)

Windspire 

met

293 7.0 4.6 0.3

Data shed 341 60.0 3.1 7.0

ARE 442 26 303.4 31.0 7.3

ARE 442 met 13 299.3 31.0 0.4

Gaia 47 168.9 18.2 13.0

Gaia met 9 153.3 8.2 0.4

NREL completed a site assessment to determine if the site fails the requirements of Annex A of 

the Standard and would therefore require a site calibration. Table 3 shows the results from the 

site assessment. Based on the site assessment results, a site calibration is not required.

Table 3. Criteria for test site without site calibration

Description Distance Sector

(deg)

Test Site 

Condition

Pass/Fail

Maximum slope of best fit plane < 3% <2L 360 2.6% Pass

Maximum variation from best fit plane < 

0.08 D

<2L 360 0.04 Pass

Maximum slope of best fit plane < 5% 2-4L In 1.7% Pass

Maximum variation from best fit plane < 

0.15 D

2-4L In 0.04 Pass

Steepest slope maximum < 10% 2-4L Out 3.4% Pass

Maximum slope of best fit plane < 10% 4-8L In 2.0% Pass

Maximum variation from best fit plane < 

0.15 D

4-8L In 0.04 Pass

No neighboring and operating turbines <2Dn 360 0 Pass

No obstacles <2De 360 0 Pass

D = test turbine rotor diameter

L = distance between test turbine and meteorological tower

De = equivalent diameter of obstacle

In = inside preliminary measurement sector

Out = outside preliminary measurement sector

The Mariah Windspire was connected to the electrical grid at a nominal voltage of 120 VAC at a 

frequency of 60 Hz. The grid tolerances are 5% for voltage amplitude and 1% for frequency.
8

5. Description of Test Equipment

All test equipment was calibrated and the calibration sheets are included in Appendix B. Table 4

shows the equipment used and calibration due dates. Figure 5 shows placement of the 

meteorological instruments on the tower. The primary anemometer was sent out for recalibration after the test period. The difference between the pre-test and post-test calibrations 

was within the tolerances allowed by the standard. 

Table 4. Equipment used in the power performance test

Instrument Make and Model Serial Number Calibration Due Date

Power transducer Second Wind, Phaser 5FM-4A20 02061 8 Feb 2009

Voltage transformers Ohio Semitronics, VT7-010E-11 08010700 Calibrated with power 

transducer

Primary anemometer Thies, First Class 0707894 27 Feb 2009

Reference 

anemometer

NRG, Max 40 179500049701

179500049703

In situ

Wind vane Met One, 020C with aluminum 

vane

W5515 27 Feb 2009

Pressure sensor

(replaced during test)

Vaisala, PTB101B C1040008

Y3350027

29 Oct 2008

29 Nov 2009

Temperature sensor 

(replaced during test)

Met One, T200 0673553

0602948

29 Oct 2008

10 Oct 2009

Precipitation sensor Campbell Scientific, 237 None In situ

Data acquisition 

system

Compact DAQ w/LabVIEW

cDAQ backplane

NI 9229

NI 9217

NI 9205

12E4D23

12B6DD2

12BD192

12E9C3E

28 Jun 2008

06 Jul 2008

08 Oct 2008

Modules post-test 

calibrated on 6 May 

2009 and found in 

compliance
9

Figure 5. Meteorological tower and instruments

To ensure that only data obtained during normal operation of the turbine are used in the 

analysis, and to ensure data are not corrupted, data sets are excluded from the database under 

the following circumstances:

• external conditions other than wind speed are out of the normal range for turbine 

operation,

• turbine cannot operate because of a turbine fault condition, and,

• turbine is manually shut down or in a test or maintenance operating mode.

Two methods are used to track when any of these conditions occur during the test. The first 

method, the logbook will be checked for such events. The other method is a signal from the 

turbine that indicates when the turbine is braked. 

Pr i mar y Anemomet er

Ref er ence

Anemomet er

Wi nd Di r ect i on

Temper at ur e

Pr essur e 1. 3m

3. 3m

4. 3m

6. 2m
10

6. Description of Test Procedure

The test was conducted according to the procedures in the Standard. The sampling rate was 

10 kHz, decimated to 40 Hz. The averaging time was 1 minute for the mean values. Standard 

deviation, minimum, and maximum values for each averaging period were also collected. 

The turbine status signal for the Windspire was obtained by checking the release of the brake. 

The status signal indicated if the turbine was braked or not.

Only database A is reported since the Windspire does not have a cut-out wind speed.

Table 5 gives the uncertainty sources and values used in the analysis.

Table 5. Uncertainty values used in the analysis

Component Uncertainty Source

Power

 Current sensor/signal 

 conditioner

6.00 W Specifications (specs)

 Power transducer 0.12% Specs

 Data acquisition 40.50 W +0.08% Specs

 Resistor 0.01% Specs

Wind Speed

 Calibration 0.02 m/s Calibration sheet

 Operational characteristics 0.05 m/s +0.52% IEC

 Mounting effects 1.00% Assumption

 Terrain effects 2.00% IEC 

 Data acquisition < 0.01 m/s Assumption

Temperature

 Temperature sensor 0.15 °C Specs

 Radiation shielding 1.15 °C Assumption

 Mounting effects 0.09 °C IEC method

 Data acquisition 0.35 °C Specs

Air Pressure

 Pressure sensor 0.20 kPa Instrument specs.

 Mounting effects < 0.01 kPa IEC method

 Data acquisition 0.06 kPa Specs
11

7. Test Results

Test results are given for two turbine configurations. The first section is for the normal 

configuration. The second section is for the power optimized configuration.

7.1. Results of Power Performance Test for the Normal Configuration

7.1.1. Tabular Results for Normal Power Production

Table 6 through Table 9 provide the power performance test results for the normal configuration 

in tabular format. Table 6 shows the binned power performance results at sea-level normalized 

air density for normal power production. Table 7 shows the binned power performance results 

for the site average air density at the NWTC for normal power production. 
12

Table 6. Performance at Sea-level air density; 1.225 kg/m3 for normal power production

Measured power curve (database A)

Reference air density: 1.225 kg/m3 Category A Category B Combined

Bin Wind Normalized Cp Number of Standard Standard Standard

Speed Power 1-Minute Uncertainty Uncertainty Uncertainty

Output Data Sets

(m/s) (m/s) (kW) (kW) (kW) (kW)

2.5 2.50 -0.01 -0.11 2343 0.00 0.04 0.04

3 2.99 -0.01 -0.06 2084 0.00 0.04 0.04

3.5 3.48 0.00 -0.02 1335 0.00 0.04 0.04

4 3.98 0.01 0.02 910 0.00 0.04 0.04

4.5 4.50 0.03 0.07 670 0.00 0.04 0.04

5 4.99 0.05 0.10 599 0.00 0.04 0.04

5.5 5.49 0.09 0.11 567 0.00 0.04 0.04

6 6.00 0.13 0.13 573 0.00 0.04 0.04

6.5 6.50 0.18 0.14 510 0.00 0.04 0.04

7 7.01 0.25 0.16 472 0.00 0.05 0.05

7.5 7.49 0.32 0.17 409 0.00 0.05 0.05

8 7.98 0.41 0.18 351 0.00 0.05 0.05

8.5 8.50 0.52 0.19 291 0.00 0.06 0.06

9 8.99 0.64 0.19 307 0.00 0.07 0.07

9.5 9.49 0.76 0.20 253 0.00 0.07 0.07

10 9.98 0.88 0.19 189 0.00 0.07 0.07

10.5 10.48 0.96 0.18 132 0.01 0.06 0.06

11 10.99 1.02 0.17 114 0.01 0.05 0.05

11.5 11.48 1.06 0.15 65 0.02 0.05 0.05

12 11.99 1.09 0.14 42 0.03 0.04 0.05

12.5 12.49 0.99 0.11 38 0.03 0.07 0.08

13 13.02 0.96 0.10 21 0.04 0.04 0.06

13.5 13.47 0.99 0.09 14 0.06 0.04 0.07
13

Table 7. Performance at site average density; 1.00 kg/m3 for normal power production

Measured power curve (database A)

Reference air density: 1.00 kg/m3 Category A Category B Combined

Bin Wind Normalized Cp Number of Standard Standard Standard

Speed Power 1-Minute Uncertainty Uncertainty Uncertainty

Output Data Sets

(m/s) (m/s) (kW) (kW) (kW) (kW)

2.5 2.50 -0.01 -0.11 2343 0.00 0.04 0.04

3 2.99 -0.01 -0.06 2084 0.00 0.04 0.04

3.5 3.48 0.00 -0.02 1335 0.00 0.04 0.04

4 3.98 0.01 0.02 910 0.00 0.04 0.04

4.5 4.50 0.02 0.07 670 0.00 0.04 0.04

5 4.99 0.04 0.10 599 0.00 0.04 0.04

5.5 5.49 0.07 0.11 567 0.00 0.04 0.04

6 6.00 0.10 0.13 573 0.00 0.04 0.04

6.5 6.50 0.15 0.14 510 0.00 0.04 0.04

7 7.01 0.20 0.16 472 0.00 0.04 0.04

7.5 7.49 0.26 0.17 409 0.00 0.05 0.05

8 7.98 0.33 0.18 351 0.00 0.05 0.05

8.5 8.50 0.42 0.19 291 0.00 0.05 0.05

9 8.99 0.52 0.19 307 0.00 0.06 0.06

9.5 9.49 0.62 0.20 253 0.00 0.06 0.06

10 9.98 0.72 0.19 189 0.00 0.06 0.06

10.5 10.48 0.78 0.18 132 0.01 0.05 0.05

11 10.99 0.83 0.17 114 0.01 0.05 0.05

11.5 11.48 0.87 0.15 65 0.01 0.05 0.05

12 11.99 0.89 0.14 42 0.02 0.04 0.05

12.5 12.49 0.81 0.11 38 0.02 0.06 0.07

13 13.02 0.78 0.10 21 0.03 0.04 0.05

13.5 13.47 0.80 0.09 14 0.05 0.04 0.06
14

Table 8 shows the annual energy production at sea-level normalized air density for normal 

power production. Table 9 shows the annual energy production at the site average air density 

for the NWTC for normal power production. A cut-out wind speed of 25 m/s is assumed for 

analysis purposes, though the turbine does not have a cut out wind speed. 

Table 8. Annual energy production (AEP) at sea-level density; 1.225 kg/m3 for normal 

power production

Table 9. Annual energy production at site average density; 1.00 kg/m3 for normal power 

production

Reference air density: 1.225 kg/m^3

Cut-out wind speed: 25.00 m/s

Hub height 

annual 

average wind 

speed 

(Rayleigh)

AEP-measured AEPextrapolated

Complete if AEP 

measured is at least 

95% of AEP 

extrapolated

m/s kWh kWh % kWh

4 615 372 61% 617 Complete

5 1,354 391 29% 1,383 Complete

6 2,120 402 19% 2,283 Incomplete

7 2,700 400 15% 3,156 Incomplete

8 3,032 385 13% 3,898 Incomplete

9 3,152 362 11% 4,459 Incomplete

10 3,126 336 11% 4,827 Incomplete

11 3,010 308 10% 5,024 Incomplete

Estimated annual energy production, database A (all valid data)

Standard Uncertainty in AEPmeasured

AEP measured assumes zero power between highest bin and cutout

AEP extrapolated assumes power in last bin between last bin and cutout

Reference air density: 1.00 kg/m^3

Cut-out wind speed: 25.00 m/s

Hub height 

annual 

average wind 

speed 

(Rayleigh)

AEP-measured AEPextrapolated

Complete if AEP 

measured is at least 

95% of AEP 

extrapolated

m/s kWh kWh % kWh

4 502 367 73% 503 Complete

5 1,106 380 34% 1,129 Complete

6 1,731 386 22% 1,864 Incomplete

7 2,204 381 17% 2,577 Incomplete

8 2,475 365 15% 3,182 Incomplete

9 2,573 342 13% 3,640 Incomplete

10 2,552 316 12% 3,941 Incomplete

11 2,457 290 12% 4,101 Incomplete

Estimated annual energy production, database A (all valid data)

Standard Uncertainty in AEPmeasured

AEP measured assumes zero power between highest bin and cutout

AEP extrapolated assumes power in last bin between last bin and cutout
15

7.1.2. Graphical Results for Normal Power Production

Figure 6 through Figure 12 show the results of the power performance test for normal power 

production in graphical format. Figure 6 shows a plot of the binned power curve normalized to 

sea level air density for normal power production. 

Figure 6. Power curve at sea-level density; 1.225 kg/m3 for normal power production

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

0 2 4 6 8 10 12 14

Power (kW), Normalized to Sea Level Air Density 

Wind Speed (m/s)
16

Figure 7 shows a plot of the binned power curve at the site average air density during the test 

period for normal power production. 

Figure 7. Power curve at site average density; 1.00 kg/m3 for normal power production

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

0 2 4 6 8 10 12 14

Power (kW), Normalized to Site Specific Air Density

Wind Speed (m/s)
17

Figure 8 shows a scatter plot of statistics for normal power production.

Figure 8. Scatter plot of mean, standard deviation, minimum, and maximum power data

for normal power production

Multiple power curves appear at the higher wind speeds. NREL did not find the cause during 

testing. 
18 

Figure 9 shows a plot of the binned coefficient of power as a function of wind speed at sea-level 

normalized air density for normal power production. 

Figure 9. Coefficient of power at sea-level density; 1.225 kg/m3 for normal power 

production 

 

0%

5%

10%

15%

20%

25%

0 2 4 6 8 10 12 14 16

Cp

Wind speed (m/s)
19

Figure 10 shows a scatter plot and binned turbulence intensity as a function of wind speed for 

normal power production. 

Figure 10. Wind turbulence intensity as a function of wind speed during for normal power 

production
20

Figure 11 shows a scatter plot of wind speed and turbulence intensity as a function of wind 

direction for normal power production.

Figure 11. Wind speed and turbulence intensity as a function of wind direction during 

test for normal power production
21

Figure 12 shows a scatter plot of binned values of rotor speed as a function of wind speed for 

normal power production.

Figure 12. Rotor speed as a function of wind speed (1-minute averages) and binned 

values for normal power production

7.2 Results of Power Performance Test for Optimized Power Production

7.2.1 Tabular Results for Optimized Power Production

Table 10 through Table 13 provide the power performance test results for the optimized power 

production in tabular format.

Wind speed m/s 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7

Rotor speed rpm 0 0 1 3 9 20 42 80 137 177 204 228 255 276

Wind speed m/s 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14

Rotor speed rpm 291 312 331 344 353 359 355 352 348 346 326 318 321 299

0

50

100

150

200

250

300

350

400

0 2 4 6 8 10 12 14 16 18 20

wind speed (m/s)

rotor speed (rpm)

Averages

Binned Values
22

Table 10 shows the binned power performance results at sea-level normalized air density for 

optimized power production.

Table 10. Performance at sea-level air density; 1.225 kg/m3 for optimized power 

production

Measured power curve (database A)

Reference air density: 1.225 kg/m3 Category A Category B Combined

Bin Wind Normalized Cp Number of Standard Standard Standard

Speed Power 1-Minute Uncertainty Uncertainty Uncertainty

Output Data Sets

(m/s) (m/s) (kW) (kW) (kW) (kW)

3 2.99 -0.01 -0.06 8497 0.00 0.01 0.01

3.5 3.48 -0.01 -0.03 6251 0.00 0.01 0.01

4 3.98 0.01 0.02 3977 0.00 0.01 0.01

4.5 4.48 0.02 0.06 2690 0.00 0.02 0.02

5 4.99 0.05 0.09 2031 0.00 0.02 0.02

5.5 5.49 0.08 0.11 1576 0.00 0.03 0.03

6 6.00 0.12 0.12 1391 0.00 0.03 0.03

6.5 6.48 0.16 0.13 1124 0.00 0.04 0.04

7 6.99 0.22 0.14 953 0.00 0.05 0.05

7.5 7.49 0.29 0.15 741 0.00 0.06 0.06

8 7.99 0.37 0.16 559 0.00 0.08 0.08

8.5 8.47 0.48 0.17 411 0.01 0.11 0.11

9 8.98 0.60 0.18 331 0.01 0.11 0.11

9.5 9.48 0.72 0.19 206 0.01 0.13 0.13

10 10.00 0.86 0.19 181 0.01 0.14 0.14

10.5 10.50 0.96 0.18 146 0.01 0.11 0.11

11 10.99 1.08 0.18 121 0.01 0.12 0.12

11.5 11.47 1.15 0.17 80 0.01 0.09 0.09

12 12.02 1.24 0.16 71 0.02 0.09 0.09

12.5 12.50 1.29 0.14 43 0.01 0.07 0.07

13 13.02 1.32 0.13 29 0.01 0.04 0.04

13.5 13.56 1.37 0.12 14 0.01 0.06 0.06
23

Table 11 shows the binned power performance results at the site average air density for the 

NWTC for optimized power production.

Table 11. Performance at site average density; 0.95 kg/m3 for optimized power production

Measured power curve (database A)

Reference air density: 0.95 kg/m3 Category A Category B Combined

Bin Wind Normalized Cp Number of Standard Standard Standard

Speed Power 1-Minute Uncertainty Uncertainty Uncertainty

Output Data Sets

(m/s) (m/s) (kW) (kW) (kW) (kW)

3 2.99 -0.01 -0.06 8497 0.00 0.01 0.01

3.5 3.48 0.00 -0.03 6251 0.00 0.01 0.01

4 3.98 0.00 0.02 3977 0.00 0.01 0.01

4.5 4.48 0.02 0.06 2690 0.00 0.02 0.02

5 4.99 0.04 0.09 2031 0.00 0.02 0.02

5.5 5.49 0.06 0.11 1576 0.00 0.02 0.02

6 6.00 0.09 0.12 1391 0.00 0.03 0.03

6.5 6.48 0.13 0.13 1124 0.00 0.03 0.03

7 6.99 0.17 0.14 953 0.00 0.04 0.04

7.5 7.49 0.22 0.15 741 0.00 0.05 0.05

8 7.99 0.29 0.16 559 0.00 0.06 0.06

8.5 8.47 0.37 0.17 411 0.00 0.08 0.08

9 8.98 0.46 0.18 331 0.00 0.09 0.09

9.5 9.48 0.56 0.19 206 0.01 0.10 0.10

10 10.00 0.67 0.19 181 0.01 0.11 0.11

10.5 10.50 0.75 0.18 146 0.01 0.08 0.08

11 10.99 0.83 0.18 121 0.01 0.10 0.10

11.5 11.47 0.90 0.17 80 0.01 0.07 0.07

12 12.02 0.96 0.16 71 0.01 0.07 0.07

12.5 12.50 1.00 0.14 43 0.01 0.05 0.05

13 13.02 1.02 0.13 29 0.01 0.03 0.03

13.5 13.56 1.06 0.12 14 0.01 0.05 0.05
24

Table 12 shows the annual energy production at sea-level normalized air density for optimized 

power production. Table 13 shows the annual energy production at the site average air density 

at the NWTC for optimized power production.

Table 12. Annual energy production (AEP) at sea-level density; 1.225 kg/m3 for optimized 

power production

Table 13. Annual energy production at site average density; 0.95 kg/m3 for optimized 

power production

Reference air density: 1.225 kg/m^3

Cut-out wind speed: 20.00 m/s

Hub height 

annual average 

wind speed 

(Rayleigh)

AEP-measured AEPextrapolated

Complete if AEP 

measured is at least 

95% of AEP 

extrapolated

m/s kWh kWh % kWh

4 569 229 40% 571 Complete

5 1,309 332 25% 1,347 Complete

6 2,127 416 20% 2,343 Incomplete

7 2,786 463 17% 3,397 Incomplete

8 3,192 476 15% 4,361 Incomplete

9 3,367 467 14% 5,139 Incomplete

10 3,376 444 13% 5,690 Incomplete

11 3,277 414 13% 6,023 Incomplete

Standard Uncertainty in AEPmeasured

AEP measured assumes zero power between highest bin and cutout

AEP extrapolated assumes power in last bin between last bin and cutout

Estimated annual energy production, database A (all valid data)

Reference air density: 0.95 kg/m^3

Cut-out wind speed: 25.00 m/s

Hub height 

annual 

average wind 

speed 

(Rayleigh)

AEP-measured AEPextrapolated

Complete if AEP 

measured is at least 

95% of AEP 

extrapolated

m/s MWh MWh % MWh

4 442 194 44% 443 Complete

5 1,015 271 27% 1,044 Complete

6 1,650 334 20% 1,817 Incomplete

7 2,160 368 17% 2,634 Incomplete

8 2,475 377 15% 3,382 Incomplete

9 2,612 369 14% 3,985 Incomplete

10 2,618 350 13% 4,413 Incomplete

11 2,542 327 13% 4,671 Incomplete

Estimated annual energy production, database A (all valid data)

Standard Uncertainty in AEPmeasured

AEP measured assumes zero power between highest bin and cutout

AEP extrapolated assumes power in last bin between last bin and cutout
25

7.2.2 Graphical Results for Power-Optimized Configuration

Figure 13 through Figure 19 show the results of the power performance test for optimized power 

production in graphical format. Figure 13 shows a plot of the binned power curve normalized to 

sea-level air density of optimized power production. 

Figure 13. Power curve at sea-level density; 1.225 kg/m3 for optimized power production

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 2 4 6 8 10 12 14

Wind Speed (m/s)

Power (kW), Normalized to Sea Level Air Density 
26

Figure 14 shows a plot of the binned power curve at the site average air density for the NWTC 

for optimized power production. 

Figure 14. Power curve at site average density; 0.95 kg/m3 for optimized power 

production

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 2 4 6 8 10 12 14

Wind Speed (m/s)

Power (kW), Normalized to Site Specific Air Density
27

Figure 15 shows a scatter plot of statistics for optimized power production.

Figure 15. Scatter plot of mean, standard deviation, minimum, and maximum power data 

for optimized power production
30 

Figure 16 shows a plot of the binned coefficient of power as a function of wind speed at sealevel normalized air density for optimized power production. 

Figure 16. Coefficient of power at sea level density; 1.225 kg/m3 for optimized power 

production 

 

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

0 2 4 6 8 10 12 14

Wind speed (m/s)

Cp
29

Figure 17 shows a scatter plot and binned turbulence intensity as a function of wind speed for 

optimized power production.

Figure 17. Wind turbulence intensity as a function of wind speed during the test for 

optimized power production
30

Figure 18 shows a scatter plot of wind speed and turbulence intensity as a function of wind 

direction for optimized power production.

Figure 18. Wind speed and turbulence intensity as a function of wind direction during the 

test for optimized power production
31

Figure 19 shows a scatter plot and binned values of rotor speed as a function of wind speed for 

optimized power production.

Figure 19. Rotor speed as a function of wind speed (1-minute averages) and binned 

values for optimized power production
32

8. Deviations and Exceptions

8.1. Deviations from the Standard

1. The current transformers are not complaint with IEC 60044-1, but do exceed the 

minimum accuracy required by the Standard.

2. For both turbine configurations, the 14 m/s wind speed bin was not filled as required 

in Annex H.

8.2. Exceptions to NWTC-CT Quality Assurance System

The data acquisition modules were used beyond the calibration due date. The modules were 

post-test calibrated and found in compliance with the specifications. The post-test calibration 

sheets are included in Appendix B.
33

A. Appendix – Pictures of the Test Site from the Turbine Base
34

Figure A.1. South-southwest

Figure A.2. South-southeast
35

Figure A.3. East-southeast

Figure A.4. East-northeast
36

Figure A.5. North-northeast

Figure A.6. Northwest
37

Figure A.7. West-northwest

Figure A.8. West
38

B. Appendix – Equipment Calibration Sheets
39

Figure B.1. Power transducer calibration sheet
40

Figure B.2. RTD probe calibration sheet I
41

Figure B.3. RTD probe calibration sheet II
42

Figure B.4. Primary anemometer calibration sheet I
43

Figure B.5. Primary anemometer calibration sheet II
44

Figure B.6. Wind vane calibration sheet
45

Figure B.7. Pressure transmitter calibration sheet
46

Figure B.8. Pressure transmitter calibration sheet II
47

Figure B.9. NI 9229 data acquisition module calibration sheet I
48

Figure B.10. NI 9217 data acquisition module calibration sheet I
49

Figure B.11. NI 9205 data acquisition module calibration sheet I
50

Figure B.12. NI 9229 data acquisition module calibration sheet II
51

Figure B.13. NI 9217 data acquisition module calibration sheet II
52

Figure B.14. NI 9205 data acquisition module calibration sheet II
F1147-E(10/2008)

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1. REPORT DATE (DD-MM-YYYY)

December 2009

2. REPORT TYPE

Technical Report

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Wind Turbine Generator System Power Performance Test Report 

for the Mariah Windspire 1-kW Wind Turbine

5a. CONTRACT NUMBER

DE-AC36-08-GO28308

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

A. Huskey, A. Bowen, and D. Jager

5d. PROJECT NUMBER

NREL/TP-500-46192

5e. TASK NUMBER

WE102211

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401-3393

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NREL/TP-500-46192

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NREL

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13. SUPPLEMENTARY NOTES

14. ABSTRACT (Maximum 200 Words)

This report summarizes the results of a power performance test that NREL conducted on the Mariah Windspire 1-kW 

wind turbine. During this test, two configurations were tested on the same turbine. In the first configuration, the 

turbine inverter was optimized for power production. In the second configuration, the turbine inverter was set for 

normal power production. In both configurations, the inverter experienced failures and the tests were not finished.

15. SUBJECT TERMS

wind energy; Mariah; Mariah Windspire 1-kW wind turbine; 1-kW wind turbine; power performance

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