Page 210 - Wind Energy Handbook

184 WIND-TURBINE PERFORMANCE

0.4 60
Measurement
Theory
0.3 40
Power coefficient 0.2 Electrical power (kW)

0.1 20 Measurement
Theory
0 0
0 2 4 6 8 10 0 5 10 15 20 25 30
Tip speed ratio Wind speed (m/s)
Figure 4.12 Comparison of Measured and Theoretical Performance Curves

60

50

40
Electrical power (kW) 30 Wind direction

SE
20 ESE
S
SSW
SW
10
WSW
W
0
0 5 10 15 20 25 30
Wind speed (m/s)
Figure 4.13 Measured Raw Results of a Three-blade Wind Turbine

4.4 Variable-speed Operation

If the speed of the rotor can be continuously adjusted such that the tip speed ratio
remains constant at the level which gives the maximum C P then the efficiency of
the turbine will be significantly increased. Active pitch control is necessary to
maintain a constant tip speed ratio but only in the process of adjustment of