Wind Characteristics - Wind Energy: Renewable Energy and the Environment - page 39

0.00-10 0.10-0.20 0.20-0.30 0.30-0.40

0.40

0.30

0.20

0.10
0.00

0

3

Oct

6

9

Jul

12

Hour

15

Apr

18

Jan

21

fiGurE 3.9 Wind shear exponent between 10 and 50 m for average month by time of day, Dalhart, Texas,
April 1996-2000.

where z 0 is the roughness parameter. Equation 3.8 allows a zero wind speed at the surface. The
roughness parameter ranges from 0.01-0.03 m for flat open terrain with short grass to larger than
1 m for rough terrain ( Table 3.4) .

ExamPlE 3.3

A met tower is located close to the edge of town. If the wind speed is 8 m/s at 10 m height, what is the
wind speed at 50 m? Use Equation 3.8 and select z 0 = 1.2.

10 m 25 m 40 m

10

9

8

7

6

0 246810 12 14 16 18 20 22

Hour

fiGurE 3.10 Annual average wind speed by time of day at 10, 25, and 40 m height, Guadalupe Pass, Texas,
1995-1999.