Wind Power Generation - Renewable Energy: Technology, Economics and Environment - page 326

tric power is thus almost equal to the installed generator capacity. The cut-out
wind speed which protects the operation phase from higher wind speeds ranges
from 24 to 26 m/s.
− Phase IV. If the wind speed exceeds a certain speed limit determined by the
converter design and type the wind energy converter must be shut down to pre-
vent mechanical deterioration. Under the described meteorological conditions
no electric power will be yielded.
On the basis of such a characteristic power curve (Fig 7.17) the electric power
generated by means of a wind energy converter within a given period of time (Fig.
7.18) can be determined if the corresponding frequency distribution of the wind
speed (Chapter 2.3.2; Fig. 2.35) is a known quantity. The frequency distribution
refers to the probability of the occurrence of a certain wind speed or a defined
wind speed interval within a given period.
Electric power output of a wind energy converter E WEC can thus be calculated
by Equation (7.22), whereas h i represents the wind occurrence probability within
a certain speed interval i within the course of period t . P el,i indicates the electric
power corresponding to the defined wind speed interval i according to the charac-
teristic power curve. The entire energy output is thus equal to the total of the re-
spective interval-specific product of the available wind quantity and correspond-
ing power within a given period over all observed wind speed intervals.

n

∑ =

E = h P t

(7.22)

WEC i el , i

i 1

c

b

a

Wind speed

Wind speed

Fig. 7.18 Determination of the energy yield (c) within a certain period by means of the
wind speed frequency distribution curve (a; see Fig. 2.35) and the characteristic power
curve (b; see Fig. 7.17) (see /7-4/)

Wind speed