Wind Energy

28 Turbulence Correction for Power Curves 161
To evaluate a power curve measured with a specific turbulence these two
factors have to be determined. Equation (28.1) can be re-written as follows:
P (v) i = P0i (¯vi)+kiσ 2 i . (28.3)
To solve this equation we need for each bin at least two sets of values. If we
have more than two sets, the redundant equations can be used to minimise
the error of the computation using the least-square method.
28.3 Results
This methodology has been applied for the turbulence intensity correction of
power curves for three different turbine types and sites:
– Stall – moderately complex, coastal terrain
– Active Stall – moderately complex, forested terrain
– Variable Speed/Variable Pitch (VS/VP) – flat, inland terrain
Data is being presented in for moderate wind speeds from 7–8 m/s. Figure 28.2
shows three curves each. The horizontal line (dashed) shows the uncorrected
P/Prated Normalised power output
P/Prated Normalised power output
0.40 Stall turbine 7-8 m/s
0.35
0.30
0.25
0.20
0.00
0.40
0.35
0.30
0.25
0.20
0.00
IEC value
Turbulence corrected power output
Turbulence binned values
0.05 0.10 0.15 0.20 0.25
Turbulence intensity [%]
Variable speed, variable pitch turbine 7-8 m/s
IEC value
Turbulence corrected power output
Turbulence binned values
0.05 0.10 0.15 0.20 0.25
Turbulence intensity [%]
P/Prated Normalised power output
0.35
0.30
0.25
0.20
0.15
0.00
Active stall turbine 7-8 m/s
IEC value
Turbulence corrected power output
Turbulence binned values
0.05 0.10 0.15 0.20 0.25
Turbulence intensity [%]
Fig. 28.2. Normalized power output (P/Prated) as function of turb. intensity at
moderate wind speeds, stall (upper left), active stall (upper right) and VS (bottom)
turbines