WIND ENERGY SYSTEMS - Cd3wd

Chapter 4—Wind Turbine Power 4–25
Figure 17: Normalized power versus normalized rated speed: (a) u c =0.5u R , u F
u c =0.4u R , u F =2u R .
=2u R ;(b)
errors in selecting a rated speed are not critical. In fact, a manufacturer could cover most
of the potential market by having only two rated speeds for a given size of turbine. A rated
speed of 11 m/s would be adequate for most sites with mean wind speeds up to 6 m/s, and
a rated speed of 13 or 14 m/s would be appropriate for sites with greater wind speeds. This
is a big help to the mass production of turbines in that it is not essential to have a turbine
specifically designed for each site. Only when a wind turbine factory is dedicated to producing
turbines for a specific wind regime, such as a large wind farm, would a more detailed design
be advisable.
It would appear from Fig. 17 that sites with lower k are superior to those with larger
k. This is true only if the mean wind speed is the same at each site. As was mentioned in
Chapter 2, sites with low mean wind speeds tend to have lower values of k than sites with
greater mean wind speeds. These lower wind speeds will usually reduce the average power
Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001