Publishers version - DTU Orbit

PP rated
PP rated
1.0
0.8
0.6
0.4
0.2
RSS0.1
RSS0.1
0.0 a
0.2 0.4 0.6 0.8 1.0 1.2
1.0
0.8
0.6
0.4
0.2
residual0.1
residual0.1
Uequ rated
0.0 c
0.2 0.4 0.6 0.8 1.0 1.2
Uequ rated
CpCp max
CpCp max
1.2
1.0
0.8
0.6
0.4
0.2
0.2 0.4 0.6 0.8
b
1.0 1.2
1.2
1.0
0.8
0.6
Uequ rated
0.4
0.2
0.2
0.4 0.6 0.8
d
1.0 1.2
Uequ rated
Figure 97: (a) Scatter plot of power curves, (b) Scatter plot of C : p curves, (c) Averaged
power curves, (d) Averaged Cp curves. These plots are obtained using the equivalent wind
speed Eq. (168) and a Cp definition taking the wind shear into account
between wind speed measured by the lidar and the cup). Lidars are very attractive because of
their capacity to measure wind speed and direction profiles with the convenience of a ground
based measurement device. However, this is still a new and rather immature technology and
it is strongly recommended to verify each instrument against a tall mast (equipped with good
wind speed sensors at several heights) in flat terrain. A remote sensing classification and a
verification procedure are currently being defined within the standard committee.
7.5 Summary
As windspeedshearinfluencesthepowerperformanceofmulti-MWturbines,itisnecessaryto
characterize the wind speed profile in front of the turbine rotor. Remote sensing instruments
are of great interest, since theycan measure the windspeed profile overthe whole rotorrange.
Such measurements avoid the use of assumptions about the shape of the wind speed profile.
A more accurate kinetic energy flux can then be calculated resulting in a better evaluation
of the power performance of the turbine. The use of an equivalent wind speed taking the
wind speed shear into account reduces the scatter in the power curve and the uncertainty in
power performance measurement. In that sense, the use of remote sensing measurements can
improve the power performance measurements. However, this can only be achieved with a
good instrument. Finally, the remote sensing instrument should not show more scatter in the
powercurve than that of a cup at a given height. This requires a verificationof the instrument
prior to the power performance measurement.
Notation
A rotor swept area
Ai area of the ith element
c chord defined by the rotor swept area
Cp power coefficient
dFD local drag force
dFL local lift force
154 DTU Wind Energy-E-Report-0029(EN)