1. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens VERIFICATION OF POWER PERFORMANCE OF ACTIVE POWER CONTROL WIND TURBINES IN COMPLEX TERRAIN N. Stefanatos, F. Mouzakis, E. Binopoulos, F. Kokkalidis, P. Papadopoulos Centre for Renewable Energy Sources (CRES) Wind Energy Department Laboratory for Wind Turbine Testing (LWTT)

2. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens Share the experience – respect confidentiality Verification of power performance in complex terrain The Laboratory for Wind Turbine Testing (LWTT) of CRES is a Testing Laboratory accredited by DAP GmbH according to ISO/IEC 17025 for wind turbine power performance measurements (and others). Numerous verifications of power curve in complex terrain sites have been successfully completed by CRES-LWTT Valuable experience gathered, but is commercially confidential Lets talk Confidential:  No site names  No wind turbine types  Non-dimensional results

3. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens Method-Standards applied IEC 61400-12:1998 MEASNET Power Performance Procedure Ver. 3/2000 IEC 61400-12-1:2005  requirements regarding instrumentation properties and positioning fulfilled Additional features  Shear profiles measured at reference mast and at wind turbine position Verification of power performance in complex terrain

4. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens CASE P1 -Pitch controlled -Fairly complex (terrain inclination typical 10%) -Only site calibration and shear results available CASE P2 Pitch controlled Semi-flat terrain (terrain inclination typical 4%) Power curve measurement campaign complete Overview of Cases studied (no photos, sorry..) Verification of power performance in complex terrain

5. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens Overview of Cases studied (no photos, sorry..) Verification of power performance in complex terrain - CASE P3 Pitch controlled Very complex terrain (terrain inclination typical 20% and higher) Power curve measurement campaign complete CASE S6 Stall controlled Extreme complex terrain (terrain inclination typical 40%) Velocity ratios direction and velocity sensitive Power curve measurement campaign complete 5 STALL CONTROL CASES Summary results from 5 older stall controlled cases also included

6. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens Verification of power performance in complex terrain Know your site (1) : Velocity ratios CASE P1 Fairly complex terrain case (10% inclination) Limited dependence of velocity ratios to mean wind speed CASE S6 Extreme complex terrain case (40% inclination) Strong dependence of velocity ratios to mean wind speed

7. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens Know your site (2) : Turbulence Verification of power performance in complex terrain Mean Turbulence levels in complex terrain sites may vary significantly (eg. from 7% to 20%)

8. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens Verification of power performance in complex terrain Know your site (3) : Shear Shear ratio from 0.80 to 0.92 Inverse shear at w/t position for one case

9. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens Verification of power performance in complex terrain Case P2 – Semi flat Terrain inclination: 4% Velocity ratio :1.01 ΔΑΕP=-0.45% Case P3 – Very complex Terrain inclination: 20% Velocity ratio: 1.17 ΔΑΕP=1.78 % Results (1) : The good, the perfect and…

10. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens Verification of power performance in complex terrain Case S6 – Stall, extreme complex Deviations  Velocity dependent site calibration factors  Working sector extended to NON-MEASNET complete direction bins to gain high wind speed bins  Warranted power curve not measured (optimised for site specific air density and wind speed annual distribution) Terrain inclination: up to 40% Velocity ratio:1.03 ΔΑΕP= - 10.9% Results (2) : … and the stall controlled

11. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens Verification of site calibration – Case S6 -Extreme Conventional site calibration Velocity-dependent s.c Verification of power performance in complex terrain Direction sensitive power curve Verification failed No direction effect on power curve Verification successful

12. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens Verification of power performance in complex terrain Effect of mast base altitude height difference on velocity ratio Small AEP deviation regardless of the Velocity ratio (for 5 stall cases also) Results 3 – Sensitivity analysis (or “stall control can be OK too…)

13. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens Verification of power performance in complex terrain Turbulence intensity : Limited effect Mast distance : No effect (within the IEC limits) Results 4 – Sensitivity analysis (or “stall control can be OK too…)

14. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens Lets get dimensional again Assume  10 MW wind farm  8 m/s Annual mean wind speed  kWh price : 0.075 EUROs  10% less AEP  Income lost per year: 200 kEUROs (many times the cost of a power curve verification campaign…) Verification of power performance in complex terrain Terrain inclination: up to 40% Velocity ratio:1.03 ΔΑΕP= - 10.9%

15. Nikolaos Stefanatos Laboratory for WT Testing (LWTT) EWEC 2006- Athens  Wide variety of flow conditions in complex terrain – not always bad  Current methods adequate to give reliable results even in difficult cases  Extreme cases do exist and require additional attention  Verification and cross-check procedures very important “A power curve verification campaign may prove to be a very good investment” Verification of power performance in complex terrain Conclusions