Introduction to Wind Turbine Technology - Small Wind Turbines: Analysis, Design, and Application - page 17

Fig. 1.8 Probability
distribution for a mean wind
speed of 5 m/s (solid line)
and the variation of
contribution to the power
output with wind speed for
the Bergey XL 10 kW turbine
(squares)

0.25

0.2

0.15

0.1

0.05

0

0 5 10 15 20

Wind speed (m/s)

favourable locations around the world, and much higher at the Australian Antarctic
Base at Mawson where the 10 m average wind speed is 14 m/s. Small wind
turbines tend to have much lower capacity factors, and a value of 0.20 is usually
regarded as ''high''. Figure 1.8 also shows another important general fact of wind
turbines: the greatest contribution to the average power comes from wind speeds
above the mean. If the rated speed is less than about twice the mean speed, then
significant reductions in capacity factor are likely. Finally, the broad spread of
possible wind speeds at most sites causes the average power output of a turbine to
have a different dependence on the average wind speed than the near cubic one
exhibited in the power curves of Figs. 1.4 and 1.5 .

1.8 The Electrical and Mechanical Layout of Wind Turbines

The generator and bulk of the mechanical components are housed in the nacelle on
top of the tower of most turbines. Much of the control electronics is also located
on top of the tower for many large and some small ones. For the Vestas V80 in
Fig. 1.9 the main component is, of course, the generator, but there are many others,
such as a gearbox (#6), which is not common on small machines and is slowly
losing favour on large machines as well. Most small turbines have little more than
the generator in the nacelle, so large turbines are significantly more complex, with,
for example, an anemometer and wind vane (#10) used in conjunction with the
hydraulic yaw gear (#17) to drive the turbine into the wind. This turbine also has
blade pitch adjustment (see #2), as do most large turbines.
The Skystream 2.4 kW turbine is unusual in having much of the elctronics
within the nacelle as shown in Figs. 1.10 and 1.11 . The bolted shaft in Fig. 1.10
holds the rotor of the permanent magnet generator with the stator attached to the
nacelle casting. The blades are attached on the shaft outside the nacelle, which is
not shown in the figure. The electronic components comprise the rectifier and