Wind Characteristics - Wind Energy: Renewable Energy and the Environment - page 44

Hours Energy

1000 600

900

500

800

700

400

600

500 300

400

200

300

200

100

100

0

0

0 5 10

Wind Speed, m/s

15 20

fiGurE 3.12 Annual average, comparison of wind speed and energy histograms at 50 m for White Deer,
Texas, 1996-1999.

3.9 duration CurVE
Wind data can also be represented by a speed-duration curve (Figure 3.13), which is a plot of cumu-
lative frequency starting at the largest wind speed (subtract 100 from percent frequencies of cumu-
lative frequencies if starting at the lowest wind speed). The percent duration is usually converted
(multiplying by 8,760) to number of hours in a year. From wind speed-duration curves, estimates of
the time the wind speed is above a given value can be obtained. The data in Table 3.5 and the curve
in Figure 3.12 show, for example, that a wind of 3 m/s or greater blows 95% of the time, or 8,300
hours in a year for that location.

100

Series 1

90

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60

50

40

30

20

10

0

0 5 10

Wind Speed, m/s

15 20

fiGurE 3.13 Wind speed-duration curve at 50 m height for White Deer, Texas, 1996-1999.