Environmental Engineering Reference
In-Depth Information
Persistence of Wind Speeds
Persistence is the duration of the wind speed within a given range. Sigl
et al.
[1979]
used hourly wind speed records to develop a model for the probability distribution of wind
speed persistence above and below fixed reference speeds, which represented the operat-
ing range of a wind turbine. Examination of duration histograms from 19 sites for records
varying from 5 to 24 years in length led to the development of a simple
composite distri-
bution
model. As shown in Figure 8-8, the probability that a run duration will exceed a
given time period is modeled by a power function for the shorter runs and an exponential
function for longer runs. The transition between the two functions occurs at a run duration
of
t
p
, referred to as the
partition parameter.
Equations for these probability functions are
F
(
t
r
£
t
) = 1- (1 -
F
p
)(
t
/
t
p
)
-
m
,
t
o
£
t
£
t
p
(8-9a)
F
(
t
r
£
t
) = 1- (1-
F
p
) exp[-m(
t
/
t
p
- 1)],
t
>
t
p
(8-9b)
t
p
=
t
o
(1 -
F
p
)
-
1/m
(8-9c)
where
F
( )
=
cumulative probability of ( )
t
r
=
run duration (h)
t =
specified time (h)
t
p
=
partition parameter (h)
F
p
=
empirical probability parameter; cumulative probability at
t
r
= t
p
µ
=
empirical shape parameter, greater than zero
t
o
=
shortest observable run duration (h)
Figure 8-8. Composite distribution model for estimating probabilities of wind speed
persistence, with comparison to sample test data.
Data are for runs at wind speeds below
4 m/s during five winters at Cheyenne, Wyoming. [Sigl
et al.
1979]
Search WWH ::
Custom Search