Environmental Engineering Reference
In-Depth Information
Figure 2-12 shows the reference frequency distributions of steady wind speed,
f
W
, and wind
power density,
e
W
, at an elevation of 10 m. The area under the latter curve equals an annual
wind energy density of 2,324 kWh/y/m
2
. The wind speed at which the energy frequency is a
maximum lies in the middle of the most energetic wind range at the design site. This speed is
designated here as the
design wind speed, U
D
, because annual energy production is usually a
maximum if a wind turbine is designed for maximum aerodynamic eficiency at
U
»
U
D
. With
the model speciied by NASA for the vertical proile of the wind speed [see Figure 8-13; Spera
and Richards 1979], frequency distributions can be calculated for any given elevation. The pa-
rameters
C
,
k
,
U
A
,
U
D
, and
e
W
for the reference wind regime are given in Table 2-1
vs
. elevation.
It can be seen that the reference wind energy density increases signiicantly with elevation.
Figure 2-12. Frequency distribution functions for wind speed and wind energy density
at the DOE/NASA Design Reference Site.
Elevation = 10 m; air density = 1.225 kg/m
3
.
Referring to Equations (2-1) and (2-3), the reference annual wind energy becomes
ò
ò
(2-9)
E
W
=
e
W
(
z
)
dA
=
e
W
(
z
)
w
(
z
)
dz
A
H
where
E
W
= reference annual wind energy input to the rotor swept area (W/y)
H
= vertical height of the swept area; includes
tilt
, if any (m)
w
= width of the swept area at elevation
z
(m)
Search WWH ::
Custom Search