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DNV GL © 2 June 2015 SAFER, SMARTER, GREENER DNV GL ©
2 June 2015 Carl Ostridge and Taylor Geer
ENERGY
What Your Anemometer Calibration Really Means
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DNV GL © 2 June 2015
Overview
Why do anemometer measurements vary?
Why does this matter?
Why are we talking about anemometers again?!
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DNV GL © 2 June 2015
Why are we talking about this again?!
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DNV GL © 2 June 2015
Why Are We Talking About This Again?!
Do all cup anemometers measure the same thing? Implications for pre-construction P50 estimates and power
performance testing – Anemometer Model + Calibration Facility could cause >2%
deviation on wind speed, 3-4% on energy. – Not all uncertainty – some biases – Disconnect between anemometer models and calibration
facilities used in pre-construction assessments and power performance testing
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No, probably not.
We are talking about this because if we aren’t careful, significant biases can enter our work.
DNV GL © 2 June 2015
Why Do Anemometer Measurements Vary?
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DNV GL © 2 June 2015
Why Do Anemometer Measurements Vary? 1. Anemometer Design & Atmospheric Conditions
Anemometer Design – Cup shape, size
– Aerodynamics
– Bearing
– Signal generation
Atmospheric Conditions – Inflow angles
– Turbulence Intensity
– Temperature
– Air Density
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DNV GL © 2 June 2015
Wind Speed and Turbulence Intensity Measurement Example
Two different anemometer models calibrated in different facilities, mounted in parallel
Strong divergence and trend at lower wind speeds, better agreement at mid to high wind speeds, still some bias in both wind speed and turbulence
Deviation in correlation may seem small, but can result in big impacts
– Long-term mean wind speed and energy – up to 3-4% energy
– Smaller impacts on loss factor calculations and turbine suitability due to turbulence intensity
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Wind speed Turbulence Intensity
DNV GL © 2 June 2015
Why Do Anemometer Measurements Vary? 2. Wind Tunnel Calibrations
Wind tunnels vary in size and design – Large variation in test cross section area between MEASNET tunnels
– A mix of open and closed test sections
– Boundary and blockage effects have been shown to influence anemometer calibrations
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T. Blodau, A. Janzen, K. Neumann: “Anemometer Calibration Variability”. DEWEK 2012.
O. Frost Hansen, S.O. Hansen and L. Kristensen: “Wind tunnel calibration of cup anemometers“. AWEA WindPower 2012.
S. Clark: “SOH Wind Engineering Qualification, Calibration, and Accreditation”, Renewable NRG Systems.
DNV GL © 2 June 2015
Wind Tunnel Calibrations – Working Group Round Robin
Working Group formed to investigate variability of calibrations seen at different MEASNET facilities
All common anemometer types and MEASNET facilities included
1 or 2 anemometers of each type sent to each facility and calibrated
Finally, each instrument is returned to the first facility and recalibrated
Working Group Members
AWS Truewind
DNV GL
NREL
Pattern Energy
Renewable NRG Systems
Siemens
SOH Wind Engineering
WSP
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DNV GL © 2 June 2015
-2%
-1%
0%
1%
2%
Dev
iation
rel
ativ
e to
ave
rage
at
8 m
/s
Facility A
Facility B
Facility C
Facility D
Wind Tunnel Calibrations – Results
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Each anemometer’s results are normalized across all facilities
Anem 1 Anem 2 Anem 3 Anem 4 Anem 5 Anem 6
DNV GL © 2 June 2015
Wind Tunnel Calibrations – Results
Slope and offset variations between tunnels cause wind speed-dependent variation in results
Deviations can exceed 1% threshold at different wind speeds
Repeatability of test results may also be anemometer-dependent
Caution required due to small sample size
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-1.50%
-1.00%
-0.50%
0.00%
0.50%
1.00%
1.50%
0 4 8 12 16 20
Dev
iation
rel
ativ
e to
ave
rage
[%
]
Wind Speed [m/s]
Facility A
Facility B
Facility C
Facility D
Facility A
Consensus
-1.50%
-1.00%
-0.50%
0.00%
0.50%
1.00%
1.50%
0 4 8 12 16 20
Dev
iation
rel
ativ
e to
ave
rage
[%
]
Wind Speed [m/s]
Facility A
Facility B
Facility C
Facility D
Facility A
Consensus
Anem 1
Anem 5
DNV GL © 2 June 2015
Wind Tunnel Calibrations – Results
Variation in calibration results between wind tunnels can approach or exceed the 1% threshold
Impact on measurements is wind speed dependent and therefore site-specific
No strong bias towards any particular anemometer or facility
Analysis is limited by small sample size and single snapshot of facility performance – time variance of calibration results not captured
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DNV GL © 2 June 2015
Why Does This Matter?
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DNV GL © 2 June 2015
Summary
A variety of factors influence the wind speeds recorded by anemometers in the field – Response to atmospheric conditions
– Calibration
Wind tunnel calibrations can vary by +/- 1% for a given anemometer type – Variation seems to be dependent on anemometer model
– Unclear impact of wind tunnel size and design
Pre-construction assessments and power performance tests impacted by anemometer type and calibration facility – Impact on P50 can be up to 3-4%, meaning €Millions in NPV of projects
– AEP can vary by ~2% for power curve tests
Reduced bias risk with mixed anemometer models and calibration facilities
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DNV GL © 2 June 2015
SAFER, SMARTER, GREENER
www.dnvgl.com
Thank you
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Carl Ostridge [email protected]
Taylor Geer [email protected]