Introduction to Wind Turbine Technology - Small Wind Turbines: Analysis, Design, and Application - page 11

Fig. 1.5 Power curve for the
Vestas V80 turbine. Data
from www.restscreen.net
(accessed 4 Apr 2010)

2000

1800

1600

1400

1200

1000

800

Cut-in wind
s peed

600

400

200

0

0 5 10 15 20

Wind speed (m/s)

Table 1.1 Power and power
coefficient variation with
wind speed for the Vestas
V80 2 MW and Bergey XL
10 kW turbines

Wind speed (m/s) Vestas V80 2 MW Bergey XL 10 kW

P (kW) C P P (kW) C P

3 0 0 0 0

4 44.0 0.228 0.3 0.203

5 135.0 0.358 0.6 0.208

6 261.0 0.401 1.8 0.361

7 437.0 0.422 2.6 0.328

8 669.0 0.433 3.5 0.296

9 957.9 0.435 4.9 0.291

10 1279.0 0.424 6.4 0.277

11 1590.0 0.396 7.7 0.251

12 1823.0 0.350 9.2 0.231

13 1945.0 0.294 10.0 0.197

14 1988.0 0.240 10.0 0.158

15 2000.0 0.196 10.0 0.128

16 2000.0 0.162 5.5 0.058

17 2000.0 0.135 2.8 0.025

Data from www.retscreen.net (accessed 4 Apr 2010)

scale. For nearly all large turbines but rarely for small ones, there is also a
''cut-out'' wind speed at which the turbine is shut down for safety reasons. This is
25 m/s for the V80 (not shown in Fig. 1.5 ). At this speed, the brake is activated,
and not released until the wind has died down. At high wind speeds, smaller
turbines such as the Bergey 10 kW, are often ''furled'', that is turned out of the
wind direction by the collapse of the tail fin as described in Chap. 8 . Other small
turbines rely on control of the generator's field current to reduce output in high
winds and shorting of the generator output for braking. This ''electrical'' rather
than ''mechanical'' or ''aerodynamic'' braking is described in Chap. 11 .
As the wind speed increases from below the cut-in, the brake on larger turbines
is released, and, the blades are pitched into the wind (this phrase should be clearer