sin αst

ROTOR
62
Figure 6.22: Efficiency �tot of the complete wind turbine
Actual performance of the wind turbine is expected to exhibit divergence from the theo-
retical performance of figure 6.20, as the assumptions and idealisations of the BEM theory
(see appendix B.1) seldom occur in reality. The variations are further amplified by the
effects of manufacturing inaccuracies and varying surface properties that cause airfoil
characteristics to change from those described in appendix D.
6.3.1 Annual energy production
The average wind turbine power output is given by the wind turbine power curve of figure
6.20 and the wind regime probability function pR(V), described in appendix A.1 [12, p. 62]
P ave
V2
�
= �
�
V1
pR( V)
Pg( V)
Pg(V) is found through regression analysis of the power curve in figure 6.20 to be
dV
Pg( V)
0.3718V 3 0.9126V 2
=
� � 2.4588V
(6.1)
(6.2)