Environmental Engineering Reference
In-Depth Information
Turbulence intensity is usually calculated for short time periods, minutes to an hour, and is the
mean wind speed divided by the standard deviation:
v
S
(3.15)
I
3.8 WIND SPEED HISTOGRAMS
A wind speed histogram shows the number of hours (or whatever time period is used) the wind
blew at each wind speed class (Table 3.5). Wind speeds were sampled at 1 Hz and averaged for 1 h,
and year wind speed histograms for 1996-1999 were averaged to obtain a representative annual
value. An average density of 1.1 kg/m
3
was used to calculate the average wind power potential.
The average wind speed was 8.2 m/s, and the average wind power potential was 467 W/m
2
for a
height of 50 m. The plots of the wind speed histogram and energy histogram (
Figure 3.12
)
show
the relationship between the two. There is little energy in low wind speeds because of the low
wind speed, and little energy at high wind speeds because of the small amount of time of high
wind speeds.
TABLE 3.5
Annual Average: Wind Speed Histogram, Frequency and Calculation of Mean Wind Speed
and Wind Power Potential at 50 m for White Deer, Texas, 1996-1999
Wind
Bin
Speed,
Duration
Class
m/s
Hours
Frequency
f
j
v
j
f
j
v
j
3
%
k
Wh/m
2
1
0.5
54
0.01
0.00
0.0
100
0
2
1.5
146
0.02
0.03
0.1
99
0
3
2.5
353
0.04
0.10
0.6
98
3
4
3.5
487
0.06
0.19
2.4
94
11
5
4.5
617
0.07
0.32
6.4
88
31
6
5.5
747
0.09
0.47
14.2
81
68
7
6.5
844
0.10
0.63
26.4
73
127
8
7.5
950
0.11
0.81
45.7
63
220
9
8.5
949
0.11
0.92
66.5
52
320
10
9.5
940
0.11
1.02
92.0
41
443
11
10.5
801
0.09
0.96
105.9
31
510
12
11.5
702
0.08
0.92
122.0
21
588
13
12.5
486
0.06
0.69
108.4
13
522
14
13.5
302
0.03
0.47
84.8
8
409
15
14.5
175
0.02
0.29
60.9
4
293
16
15.5
85
0.01
0.15
35.9
2
173
17
16.5
52
0.01
0.10
26.9
1
130
18
17.5
32
0.00
0.06
19.6
1
94
19
18.5
22
0.00
0.05
15.7
0
76
20
19.5
12
0.00
0.03
10.5
0
51
21
20.5
4
0.00
0.01
3.6
0
17
Sum
8,760
1
8.2
849
4,088
Power/area
467
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