# Small System Resource Assessment

```Southwest Windpower, Inc.
The basics of wind energy and
recommendations to installing
Small Wind Systems
Wind is a form of Solar Energy
REFLECTED TO SPACE
53,000
KINETIC ENERGY
350
GEOTHERMAL
HEAT 30


178,000
82,000
PHOTOSYNTHESIS
100
HEAT FROM EVAPORATION
40,000
TIDES 3
ABSORBED
120,000
Wind is solar energy transformed to kinetic energy
Earth absorbs 120,000 terawatts (120·1015 watts) of energy
from the sun. 0.3% is transformed into wind. This is 26
times the world’s current energy use.
The details of wind
energy that you really don’t need to
worry about but is good to know
Wind energy in scientific notation
2
= 1/2mv
3
K.E. of wind = 1/2pAv t
– p= density of air
K.E.
– A = swept area
– v = wind velocity
Power
= K.E. of wind/time
Wind speed -and- Potential Energy
Energy Available in the wind follows the equation
½ (air pressure) x 3.14 (pi) x (blade length)2 x (wind velocity)3
2
Power in 1 m at a wind speed of 3 m/s:
3
0.5 x 1.204 x 3.14 x 12 x 3 = 51 W
2
Power in 1 m at a wind speed of 5 m/s
0.5 x 1.204 x 3.14 x
12
x 5 = 236
3
W
Beware of turbines that claim great low wind
speed performance – only 51 Watts are
available at 3 m/s using a 1 m blade!
Wind speed -and- Potential Energy
Energy Available in the wind follows the equation
½ (air pressure) x 3.14 (pi) x (blade length)2 x (wind velocity)3
2
Power in 1 m at a wind speed of 4 m/s:
3
0.5 x 1.204 x 3.14 x 12 x 4 = 121 W
2
Power in 1 m at a wind speed of 8 m/s
0.5 x 1.204 x 3.14 x
12 x
8 = 968
3
W
Every time wind velocity doubles,
available energy increases 8 times!
Swept Area -and- Potential Energy
How does Swept Area affect Potential Energy? How does a 1 m
2
Power in 1 m at a wind speed of 5 m/s:
3
2
0.5 x 1.204 x 3.14 x 1 x 5 = 236 W
2
Power in 1.5 m at a wind speed of 5 m/s
0.5 x 1.204 x 3.14 x 1.52 x 5 = 532
3
W
Swept Area is the best way to determine Turbine
Performance at normal wind speeds (sub 18 mph avg.)
[Keep this fact in mind when comparing the Whisper H40 with the Whisper H80!]
Betz Limit
The maximum amount of energy that may be extracted from the wind
utilizing a wind turbine is 59% of Available Energy.
Most commercial turbines hover in the 20-35% efficiency
(extracted energy divided by available energy).
How do SWWP Turbines fare at 5 m/s?
AIR X
H40
H80
175
Eff.
Actual
Betz Lmt.
Available
31%
31%
28%
35%
30 W
80 W
150 W
420 W
58 W
154 W
314 W
706 W
98 W
260 W
531 W
1196 W
Frequency at which the wind blows
Weibull Distribution
From Hybrid Power Design Handbook, by C.D. Barley
WIND SPEED AVERAGE IN METERS PER SECOND – M/S
All 3 curves have the same Average Wind Speed, but will vary
greatly in energy available. K=2.5 shows more consistent winds.
However, the more gusty site with k=1.5 contains significantly more
energy because of the greater occurrences of 10+ m/s velocities.
Roughness for flat terrain
Roughness
Water or ice
Wind shear
exponent
0.1
Low grass or steppe
0.14
Rural with obstacles
0.2
Suburb and woodlands
0.25
Wind speed change with height
V = Vo(H/Ho)
HEIGHT
(ft)
90
60
30
0
WINDSPEED
(mph)
13.5
12.9
12.2
10
surface
Tall towers matter – each 30 foot increase in height
will result in another 25% Energy Output!
The Details in Wind
energy that you really do need to know
Elevation
Tower
height
Wind speed average
Elevation
Altitude: Density decreases with altitude
Output compared to power curve
1-500 feet
1-150 meters
100%
500-1000 feet
1000-2000 feet
2000-3000 feet
3000-4000 feet
4000-5000 feet
5000-6000 feet
7000-8000 feet
8000-9000 feet
9000-10,000 feet
150-300 meters
300-600 meters
600-900 meters
900-1200 meters
1200-1500 meters
1500-1800 meters
2100-2400 meters
2400-2700 meters
2700-3000 meters
97%
94%
91%
88%
85%
82%
79%
73%
70%
Siting wind – It really is easy
Barriers to wind flow

Barriers produce disturbed areas of airflow
downwind which are called wakes. In barrier
wakes, wind speed is reduced and rapid changes in
wind speed and direction, called turbulence, are
increased.
Building Obstructions
Good location for
wind turbine
Good location for
wind turbine
PREVAILING
WIND
Turbulence
Turbulence
20H
Undisturbed upstream
wind speed profile
High
Turbulence
5H
15H
Turbulence
10H
5H
Turbulence
Turbulence
H
2H
2H
2H
Region of Highly
Disturbed Flow
10H
15H
Speed
Decrease
17% 6%
3%
Turbulence
Increase
20% 5%
2%
Wind Power
Decrease
43% 17% 9%
Appropriate maximum values depend
Upon building shape, terrain and other
Nearby obstacles.
Siting behind a row of trees
The region underneath the curve has too much turbulence, and is not a good site to install a wind turbine. This
Region is determined by the height (H) of the tallest tree. The region with the straight, smooth lines ABOVE the
Curve has air flow that is laminar, free flowing, which is IDEAL for a wind turbine.
Good location for
LEEWARD
WINDWARD
wind turbine
Good location for
wind turbine
Turbulent
Region
Good location for
wind turbine
H
Turbulent
Region
Turbulent
Region
Wind
Direction
5H
10-15 H
Streamers and turbulence
Kite
Smooth Flow
(Good height to install a
Southwest Windpower Turbine)
Top of barrier-induced turbulence
Predominant wind direction
Turbulent
Flow
By using a kite and adding streamers to the
line you can determine the area behind trees
or buildings where turbulence is present. The area
with smooth air flow will have a straight streamer as
opposed to turbulent streamers that are flapping
constantly.
Acceleration over a ridge
Crest of Windflow (also region of maximum wind acceleration)
Wind
Speed
Possible High
Turbulence
Crest of Ridge
120%
100%
Wind
Speed
50%
200%
Airflow over cliffs
= Turbulence
(A)
(B)
(C)
(D)
Valleys between mountains
Prevailing
winds
Zone of accelerated air flow
Mountains
Plains
Plains
(A)
Mountains
Valleys can be areas of
high wind speeds when
winds are funneled and
accelerated because of
the topography (valleys Plains
between mountains)
Zone of high wind velocities
Mountains
Valley
(B)
Mountains
Prevailing Winds
Siting using vegetation
 Brushing:
Branches and twigs bend
downwind.
 Flagging: Branches stream downwind,
upwind branches are short
 Throwing: A tree has trunk and branches
bent downwind
 Carpeting: Winds are so strong it will not
allow vertical growth of tree
Deformation Ratio
D = A/B + C/45
Prevailing
Wind
Direction
C
B
Deformation Ratio
Probable Mean Annual
Wind Speed Range
(MPH)
A
I
5-9
II
III
8-11 10-13
IV
V
VI
12-16
14-18
15-21
Source: Data prepared by E.W. Hewson, J.E. Wade, and R.W. Baker of Oregon State University.
Griggs-Putnam Index
Prevailing Wind
0
No Deformity
I
II
Brush and Slight
Flagging
III
Slight
Flagging
IV
Moderate
Flagging
Complete
Flagging
V
VI
VII
Partial
Throwing
Complete
Throwing
Carpeting
The degree to which conifers have been deformed by the wind can be used
as a rough gauge of average annual wind speed. (Battelle, PNL)
Wind
Speed
Index
I
MPH
7-9
9-11
11-13
m/s
3-4
4-5
11-14
14-18
Km/h
II
III
IV
V
VI
VII
13-16
15-18
16-21
22+
5-6
6-7
7-8
8-9
10+
18-21
21-25
25-29
29-32
36+
Siting with no vegetation
Observations
Wind speed (m/s)
Calm; smoke rises vertically
0.0 – 0.2
Smoke drift indicate wind direction
0.3 – 1.5
Wind felt on face; vanes begin to move
1.6 – 3.3
Light flags extended
3.4 – 5.4
Leaves and loose paper raised up
5.5 – 7.9
If your customer can fly a flag,
they can run wind turbine!
In a nutshell – it is just common sense
 Know
– Wind maps
– Local weather or television station
– Local airport
 Site
tower 30’ (9 meters) above any
surrounding object within a 300 foot radius
 Know the elevation to estimate energy loss
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