Turbulence and Heterogeneous Wind Conditions in the Field of Wind Energy MSc Thesis Presentation Robin Keus Wednesday, 17 May 2017 Supervisors: Dr. Ir. W.A.A.M. Bierbooms, TU Delft Drs. J. P. Coelingh, Vattenfall

Conditions under which turbine performance is guaranteed should be improved Power curve only guaranteed in 30% of the operating time Need turbulence normalisation! Source: Windpower

Content Background Methodology Results Conclusions

Background

Power Curve Verification Monitoring wind turbine performance Operator strives for best turbine performance Source: Vestas

Monitoring wind conditions IEC-certified met-mast Lidar Spinner anemometers

Met-mast Cup anemometers and wind vanes Limited in height Foundation Building permits Costs Source: SgurrEnergy

Lidar Aerosols Doppler shift Flexible Range Nacelle-based (optional) Five-beam Lidar: Shear Performance Source: Unitte

Sonic spinner anemometers Sound pulses Mounted on the spinner Undisturbed measurements Calibrate spinner design Source: Pedersen et al. [2015] Source: iwrpressedienst

Innovative measurement devices Still uncertain measurement accuracy Turbulence measurements of Lidar Different method Volume averaging Require more research!

Power curves depend on turbulence TI effect on power curve IEC standard turbulence normalisation procedure Reduce power curve uncertainty 4 m/s: 200 kW -270 kW 5 m/s: 470 kW 6 m/s: 840 kW +340 kW Vavg=5 m/s: 503 kW > 470 kW 𝜎=0.8 𝑚/𝑠 𝑇𝐼= 𝜎 𝑉 𝑎𝑣𝑔 =0.16 Power (kW) Wind speed (m/s) Source: Kaiser

Homogeneous wind conditions LOS 2 experiences the same wind conditions as LOS 1 LOS 2 LOS 1

Heterogeneous wind conditions LOS 2 experiences different wind conditions than LOS 1 LOS 2 LOS 1

Research Main topic: Objectives: To what extent can a (nacelle-based) Lidar measure YM and TI accurately compared to other measurement devices and what is the effect of heterogeneity on its measurements, as well as turbulence normalisation on turbine power performance? Objectives: Difference in PCV between Lidar and met-mast? Accuracy in measuring wind conditions and PCV of five-beam Lidar compared to other Lidar, spinner anemometers and met-mast? Effect of turbulence normalisation on the turbine performance and AEP? Effect on the scatter around the power curve? Can heterogeneity be quantified? Effect on Lidar measurements?

Methodology

Overview of research Prinses Alexia: Nørrekær Enge: Experience and knowledge with Lidar measurements Nørrekær Enge: Comparison of met-mast, Lidars and spinner anemometers Turbulence normalisation Validation heterogeneity

Nørrekær Enge Flat site Nacelle-based Lidars Spinner anemometers Avent 5-beam Lidar ZephIR Lidar Spinner anemometers Met-mast close to turbine 4 13 2.3MW Siemens turbines

Simulations for turbulence norm IEC procedure PC uncertainty Site-specific TI for PC Steps: Determine site TI Determine zero TI power curve Normalise power curve to site TI Zero TI PC – Measured PC (%)

Simulations for heterogeneity Synthetic wind field Approach the heterogeneity effect on Lidar measurements Possibility to correct for heterogeneity Linear Non-linear α x α x2 x1

Results

Wind speed comparison Good comparisons between Lidars and spinner anemometers with met-mast Slight overestimation of Avent Lidar Avent Lidar ZephIR Lidar ROMO spinner

Yaw misalignment comparison Spinner anemometer shows good comparison with met-mast Lidars show poor accuracy Avent Lidar ZephIR Lidar ROMO spinner

Turbulence intensity comparison Unfiltered and filtered measurements Avent Lidar compared best with met-mast ZephIR underestimates TI Spinner average TI is close to unity, but high scatter Avent Lidar ZephIR Lidar ROMO spinner

PCV Nørrekær Enge Better than guarantees Underestimation in AEP by Avent Lidar compared to met-mast (-3.5%) Overestimation by spinner (+2%) P – Pguaranteed(%)

Turbulence normalisation Simulations Effect of TI Improvement in scatter Zero TI PC – Measured PC (%) σPower/Prated

Turbulence normalisation Measurements Effect of TI No improvement in scatter Other factors influence power output Zero TI PC – Measured PC (%) σPower/Prated

Heterogeneity Simulations: Measurements: Only significant heterogeneity in wind field affects Lidar Possible to quantify heterogeneity In case of linear heterogeneity a correction is feasible Measurements: No significant impact of heterogeneity on Lidar measurements LOS 2 LOS 1

Conclusions

Measurement devices Good accuracy in measuring wind speed Poor accuracy of Lidars in YM Spinner anemometer shows better correlation with met-mast regarding YM Avent Lidar TI shows some correlation with met-mast ZephIR and spinner anemometer show low accuracy in TI

PCV Underestimation of PC by Avent Lidar Spinner anemometer overestimated PC

Turbulence normalisation Simulations showed TI effects clearly Improvement in scatter and uncertainty Measurements susceptible to other factors besides TI Possible to determine site-specific PC based on TI

Heterogeneity Possible to quantify heterogeneity Only significant heterogeneous wind conditions lead to uncertainty in measurements Corrections sensitive to wind field heterogeneity

Recommendations Perform measurements in complex terrain Investigate turbulence normalisation by isolating effects of TI on power curve Improve heterogeneity simulations Change reference point wind speed to wind conditions experienced by a turbine rotor

Thank you for your attention!

Research objectives 1. What is the difference in PCV between a ground- or nacelle-based Lidar and a met-mast? 2. How does accuracy in measuring wind conditions and PCV of a five-beam Lidar compare to other nacelle-based Lidar, spinner anemometers and IEC-compliant met-masts? 3. What is the effect of turbulence normalisation on the turbine performance and AEP? And how does it affect the scatter around the power curve? 4. Can heterogeneity be quantified? And what is its effect on Lidar measurements?

Lidar measuring volumes

Lidar derivations

Site layout Prinses Alexia Ground-based Lidar 36 3.4MW Senvion turbines

Data synchronisation

Results wind speed validation >3.5 m/s Lidars vs spinner Lidars

Results YM validation Avent vs ZephIR Lidars vs spinner

Results TI validation

Results PCV

Results inner-outer conditions Prinses Alexia Met-mast Lidar

Turbulence normalisation

TI normalisation procedure Avent ZephIR Spinner Met-mast

TI normalisation zero TI Avent ZephIR Spinner Met-mast

Heterogeneity Non-linear adjustment for heterogeneity Linear simulations Non-linear simulations