Environmental Engineering Reference
In-Depth Information
Table 2-1. Parameters of the DOE/NASA Reference Wind Regime
vs.
Elevation
Elevation
Scale
Shape
Average Speed
Design Speed
Energy Density
z
(m)
C
(m/s)
k
U
A
(m/s)
U
D
(m/s)
e
W
(kWh/m
2
/y)
5
6.30
2.16
5.58
8.55
1,656
10
7.17
2.29
6.35
9.45
2,324
15
7.73
2.37
6.85
10.05
2,836
20
8.16
2.43
7.24
10.50
3,276
25
8.51
2.48
7.54
10.85
3,664
30
8.80
2.52
7.80
11.15
4,009
35
9.06
2.56
8.04
11.40
4,331
40
9.28
2.59
8.24
11.65
4,621
45
9.49
2.62
8.44
11.85
4,907
50
9.68
2.64
8.60
12.00
5,183
55
9.85
2.67
8.76
12.20
5,425
60
10.01
2.69
8.90
12.35
5,669
65
10.16
2.71
9.03
12.50
5,902
70
10.30
2.73
9.16
12.65
6,123
75
10.44
2.75
9.29
12.77
6,350
80
10.56
2.77
9.40
12.90
6,545
85
10.68
2.79
9.51
13.00
6,744
90
10.80
2.80
9.61
13.10
6,958
95
10.91
2.82
9.72
13.22
7,145
100
11.01
2.83
9.81
13.30
7,327
For example, taking
e
W
from Table 2-1 and performing the integrations numerically, the
reference annual wind energy inputs to the Mod-5B HAWT and the 34-m VAWT are
Mod-5B HAWT:
12.2
m
£
z
£ 109.7
m
,
A
= 7, 470
m
2
:
E
W
= 41, 710
MWh
/
y
(2-10a)
34-m VAWT:
7.1
m
£
z
£ 49.0
m
,
A
= 955
m
2
:
E
W
= 3, 640
MWh
/
y
(2-10b)
Estimating Rotor Shaft Power
Rotor shaft power is the resultant of the aerodynamic
lift and drag forces
acting on the
turbine blades and transmitted by them to the rotor hub. Lift forces act at right angles to the
wind vector at the blade section, and drag forces act in the same direction as the local wind
vector. Computer models for estimating rotor power are usually based on
strip theory
, in
which each incremental length or “strip” of each rotor blade is assumed to produce aerody-
namic forces independently of all other strips and blades. This assumption has been found to
be satisfactory for analyzing the performance of modern wind turbine rotors with relatively
low
solidity,
which is the ratio of the total
planform
(maximum projected) areas of the blades
to the swept area of the rotor.
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