What Your Anemometer Calibration Really Means

Transcription

1 ENERGY What Your Anemometer Calibration Really Means Carl Ostridge and Taylor Geer 2 June DNV GL 2 June 2015 SAFER, SMARTER, GREENER

2 Overview Why are we talking about anemometers again?! Why do anemometer measurements vary? Why does this matter? 2

3 Why are we talking about this again?! 3

4 Why Are We Talking About This Again?! Do all cup anemometers measure the same thing? No, probably not. 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 We are talking about this because if we aren t careful, significant biases can enter our work. 4

5 Why Do Anemometer Measurements Vary? 5

6 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 6

7 Wind Speed and Turbulence Intensity Measurement Example Wind speed Turbulence Intensity 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 7

8 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 T. Blodau, A. Janzen, K. Neumann: Anemometer Calibration Variability. DEWEK O. Frost Hansen, S.O. Hansen and L. Kristensen: Wind tunnel calibration of cup anemometers. AWEA WindPower S. Clark: SOH Wind Engineering Qualification, Calibration, and Accreditation, Renewable NRG Systems. 8

9 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 9

10 Wind Tunnel Calibrations Results 2% Each anemometer s results are normalized across all facilities Deviation relative to average at 8 m/s 1% 0% -1% Facility A Facility B Facility C Facility D -2% Anem 1 Anem 2 Anem 3 Anem 4 Anem 5 Anem 6 10

11 Wind Tunnel Calibrations Results Deviation relative to average [%] 1.50% 1.00% 0.50% 0.00% -0.50% -1.00% -1.50% Wind Speed [m/s] Anem 1 Facility A Facility B Facility C Facility D Facility A Consensus Slope and offset variations between tunnels cause wind speed-dependent variation in results Deviations can exceed 1% threshold at different wind speeds Deviation relative to average [%] 1.50% 1.00% 0.50% 0.00% -0.50% -1.00% -1.50% Wind Speed [m/s] Anem 5 Facility A Facility B Facility C Facility D Facility A Consensus Repeatability of test results may also be anemometer-dependent Caution required due to small sample size 11

12 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 sitespecific 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 12

13 Why Does This Matter? 13

14 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 14

15 Thank you Carl Ostridge Taylor Geer SAFER, SMARTER, GREENER 15