Environmental Engineering Reference
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10000
10000
IEC Small WT
1000
1000
100
100
10
10
1
1
0.1
1
10
100
V=7 m/s
V=10 m/s
V=13 m/s
Swept Area
0.1
0.1
0.01
0.01
Rotor Diameter [m]
Figure 4: Relation between rotor diameter and power or rotor swept area.
Table 1: Sub-classifi cation of SWT.
Sub-class
Rotor diameter
Technical feature
Micro wind turbine
D < 1.6 m*
Both size and power are very small
Mimi wind turbine
1.6 m
D < 5 m
Full or small Reynolds number problem
SWT
D < 16 m** Less small Reynolds number problem
* In IEC 61400-2, a rotor swept area smaller than 2 m 2 , which corresponds to 1.6 m in
diameter, is specially classifi ed in such a way that the maximum yaw rate shall be 3 rad/s.
5 m
200(4 /
p
)
=
15.96
16.
**
effi ciency and rotor swept area. IEC defi nition of SWT is 200 m 2 of rotor swept
area which corresponds to 16 m of rotor diameter and to 10-100 kW of power
output depending on the rated wind speed.
Based on the above technical reason, some fi ner classifi cation for SWT is desir-
able. Considering both Figs 3 and 4, an idea of sub-classifi cation for small WT is
shown in Table 1.
2 Other technical problems particular with SWTs
A non-dimensional design of wind turbines gives optimal power coeffi cient for a
given tip speed ratio if the rotor performance is not affected by Reynolds number.
At design point, design tip speed ratio l D is given as:
R
L
Ω
D
l
=
(3 )
D
D
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