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ME 417
Design of Alternative Energy Systems
Wind Energy Calculations
Effect of Elevation on Wind Speed
To calculate the wind speed at one height, if it is known at another height, we can
use
n
1
2
1
2
h
h
v
v
=
r
r
where n is the ground surface friction coefficient and takes on different values
according to the nature of the terrain.
Some example values are
water or smooth flat ground: n = 0.1
tall crops: n = 0.2
city downtown: n = 0.4
Wind Power
The power of the wind can be calculated from
3
v
A
2
1
W
r
&
ρ
=
where
ρ
: density of the air
A: capture area of the wind
v
r
: wind speed
Wind Turbine Efficiency
The efficiency of a wind turbine is defined as
3
wt
wt
v
A
)
5
.
0
(
W
power
wind
produced
power
turbine
ind
w
r
&
ρ
=
=
η
Then the power of a wind turbine is given by
3
wt
wt
v
A
2
1
W
r
&
ρ
η
=
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ME 417 Design of Alternative Energy Systems
2
The efficiency for several different types of wind turbines is given in the figure
below.
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 Spring '07
 SOMERTON
 Wind turbine, Windmill

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