sin αst

pR(V) is found in appendix A.1 to be
Where Vave is the average wind speed at the site, equal to 6 m/s.
ROTOR
The integral of (6.1) is calculated from generator cut-in at V1 = 4 m/s to V2 = 14 m/s, where
furling is initialised (see section 7.1 and 8.2).
Multiplication of this by 8760 h yields the annual energy production for the site defined in
appendix A.1.
P ave
pR( V)
(6.3)
(6.4)
(6.5)
The above annual energy production is a conservative assessment, as the wind turbine still
produces power beyond 14 m/s, where furling is initiated. The produced power beyond
furling will presumably be less than the maximum power generated at 14 m/s. Moreover
wind speeds above 14 m/s only occur 1.4% of the time for the installation site specified in
appendix A.1, which renders the power produced above the furling limit negligible. The
annual energy production of the wind turbine can be optimised by trimming the character-
istics of the generator, to make the best possible fit to the characteristics of the rotor (or
vice versa). The cut-in wind speed of the generator, currently 4 m/s, may also be lowered
to improve annual energy production, although the power available at low wind speeds is
close to insignificant. It should be noted that the expected power output divergence, de-
scribed in the previous section, also is applicable to the annual energy output.
The average wind turbine power Pave (or the annual energy production) may also be used
to calculate a related performance parameter, the capacity factor, CF. The capacity factor is
the ratio of actual productivity to the rated productivity:
�
�
2
V
2
Vave e
2
� V
� � �
� �
4 � Vave �
4 m
14
s
m
� s
�
=
�
pR( V)
Pg( V)
dV
= 107W
�
E ann
= Pave8760h = 935kWh
Pave CF = =
0.07
1500W
A capacity factor of 7% is relatively low. Typical capacity factors for larger wind turbines
are 20-40%, with values in the upper end of the range in particularly favourable sites [32].
(6.6)
For the present turbine the low capacity factor is caused mainly by the generator efficiency
of 45% and the low average wind speed of the installation site. If hypothetically only con-
63