Publishers version - DTU Orbit

Height Height Hub
1.6
1.4
1.2
1.0
0.8
0.6
model:Α 0.33
mast measurement
0.4
0.6 0.7 0.8 0.9 1.0 1.1 1.2
UU rated
1.6
1.4
1.2
1.0
0.8
0.6
model:Α 0.4
mast measurement
0.4
0.6 0.7 0.8 0.9 1.0 1.1 1.2
UU rated
Figure 91: Two examples of profiles and their fit to the power law model (using the wind
speed values at 40 and 80 m). The model fits very well the measured profile on the left, but
it does not work for the profile on the right
profiles number
10
8
6
4
2
Height Height Hub
0
0.4 0.2 0.0 0.2 0.4
wsp error at 1.45 hub height
Figure 92: Distribution of the error made on the wind speed at 116.5mheight when assuming
a power law profile with a shear exponent estimated with the wind speeds at 40 and 80 m
evaluated the goodness of fit with the residual sum of squares RSS, defined as:
RSS =
(ufit(zi)−ui) 2 , (164)
i
where ufit is the fit function defined in Eq. (163) and ui the wind speed measured by the
lidar at height zi (i = 1 to 9). Figure 93 shows two examples of measured profiles with their
shear exponents and RSSs.
The profiles were then divided into two groups according to the RSS:
• Group 1: RSS ≤ 0.1 – the profiles from this group have a shape close to a power law
profile and are referred to as the power law profiles.
• Group 2: RSS > 0.1 – the profiles from this group have a shape that cannot be well
represented by a power law profile and are referred to as the non power law profiles.
DTU Wind Energy-E-Report-0029(EN) 149