How appropriate are sales power curves on complex or forested sites? Tomas Blodau July 2 nd 2012

Agenda Rotor Aerodynamics PC Measurement Analysis Alternative Techniques for PC Measurement Summary 2

Turbulence intensity Rotor Aerodynamics Variable Site Conditions All sites show varying wind conditions Turbine design needs to account for this. Wind Speed 3

c_l [-] Rotor Aerodynamics Influence of profile properties u α Des,hist α PostStall α Stall α Stall historic profile current REpower profile u α Des,RE PostStall v1 v1 v1 v1 lift coefficient over angle of attack Lift = ρ/2 A c L v r 2 REpowers philosophy is to have a sufficient angle margin to stall. smooth stall behaviour. α Design, REpower α Design historic α Stall α PostStall currentl REpower profile alpha [ ] historic wind power profile 4

c_l [-] Rotor Aerodynamics Airfoil characteristics section A-A u α V 1,HH = const v 1,upper blade section A-A no shear section B-B lift coefficient over angle of attack u α v 1, lower blade section B-B α A-A = α B-B alpha [ ] 5

c_l [-] Rotor Aerodynamics Airfoil characteristics shear influence section A-A V 1,HH =const u α v 1,upper blade section A-A very normal high shear (IEC) shear exponent = 0.4 0.6 0.2 section B-B lift coefficient over angle of attack u α v 1, lower blade section B-B α B-B α A-A alpha [ ] 6

c_l [-] Rotor Aerodynamics Airfoil characteristics roughness influence section A-A u α V 1,HH = const v 1,upper blade section A-A high shear section B-B influence of roughness on lift u α v 1, lower blade section B-B α B-B α A-A alpha [ ] clean rough 7

Rotor Aerodynamics Stall power and aerodynamic safety factor u chord u chord α Des α Des short chord (slender blade design) v1 v1 REpower design Lift = ρ/2 A c L v r 2 A = f(,chord) Chord Profile Thickness Contamination Sensitivity Stall Power Loads 8

mechanical rotorpower Rotor Aerodynamics Stall power and aerodynamic safety factor Mechanical rotorpower against wind at nominal rotorspeed and design blade set angle sufficent stall power insufficent stall power nominal power 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 wind (m/s) For high performance under varying conditions REpower blades are designed with high Aerodynamic Safety Factors 9

Rotor Aerodynamics Aerodynamic safety factors Wind turbine using REpower blade design (no stall effects seen) Wind turbine showing stall effects 10

PC Measurement Analysis Measured power curves - practice 13

PC Measurement Analysis Power curve verification reference list 14

Alternative Techniques for PC Measurement Power curve verification today Met mast is industry standard and is required by the IEC 61400-12-1. 16

Alternative Techniques for PC Measurement Power curve verification Nacelle Anemometer IEC 61400-12-2 nearly complete (FDIS) Very high uncertainty approach: 15 to 20% uncertainty 17

Alternative Techniques for PC Measurement Power Curve Measurements Anticipated Development 1. Current Status 2. Draft IEC 3. Future I 4. Future II A 9 A 8 A 7 A 6 A 5 A 4 TE HU A 3 PA A 2 A 1 TE HU PA 18

Alternative Techniques for PC Measurement Power curve verification Sample comparisons show promising results: Normalized AEP compared to guaranteed power curve (100 %) Met mast LiDAR (Hub height) LiDAR (Equivalent wind speed) 103.5 % 102.7 % 101.1 % 100.0 % 99.4 99.0 19

Alternative Techniques for PC Measurement Power curve verification future Stand alone ground based LiDAR will be acceptable Further in the future nacelle based LiDAR (of special interest offshore) 20

Summary Wind conditions are highly variable on all sites Good aerodynamic blade design can handle highly variable conditions Power curve measurement show stable results for a wide variety of conditions 22

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