1. Southwest Windpower, Inc.
The basics of wind energy and recommendations to installing Small Wind Systems

2. Wind is a form of Solar Energy
REFLECTED TO SPACE
53,000
SOLAR RADIATION
178,000
RERADIATED HEAT
82,000
PHOTOSYNTHESIS
100
KINETIC ENERGY
350
HEAT FROM EVAPORATION
40,000
TIDES 3
GEOTHERMAL
HEAT 30
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.

3. The details of wind
Important information about wind energy that you really don’t need to worry about but is good to know

4. Wind energy in scientific notation
K.E. = 1/2mv2
K.E. of wind = 1/2pAv3t
p= density of air
A = swept area
v = wind velocity
Power = K.E. of wind/time

5. 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
Power in 1 m2 at a wind speed of 3 m/s: 0.5 x x 3.14 x 12 x 33 = 51 W Power in 1 m2 at a wind speed of 5 m/s x x 3.14 x 12 x 53 = 236 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!

6. 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
Power in 1 m2 at a wind speed of 4 m/s: 0.5 x x 3.14 x 12 x 43 = 121 W Power in 1 m2 at a wind speed of 8 m/s 0.5 x x 3.14 x 12 x 83 = 968 W
Every time wind velocity doubles,
available energy increases 8 times!

7. Swept Area -and- Potential Energy
How does Swept Area affect Potential Energy? How does a 1 m
blade compare with a 1.5 m blade?
Power in 1 m2 at a wind speed of 5 m/s: 0.5 x x 3.14 x 12 x 53 = 236 W Power in 1.5 m2 at a wind speed of 5 m/s 0.5 x x 3.14 x 1.52 x 53 = 532 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!]

8. 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?
Eff. Actual Betz Lmt. Available
AIR X 31% 30 W W W
H40 31% W W W
H80 28% 150 W W W
% 420 W W W

9. Weibull Distribution
Frequency at which the wind blows
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.

10. Roughness for flat terrain

11. Wind speed change with height
V = Vo(H/Ho)
HEIGHT WINDSPEED
(ft) (mph)
13.5 90
12.9 60
12.2 30 10
surface
Tall towers matter – each 30 foot increase in height
will result in another 25% Energy Output!

12. The Details in Wind Elevation Tower height Wind speed average
Important information about wind energy that you really do need to know
Elevation
Tower height
Wind speed average

13. Elevation Altitude: Density decreases with altitude
Output compared to power curve
1-500 feet meters 100%
feet meters 97%
feet meters 94%
feet meters 91%
feet meters 88%
feet meters 85%
feet meters 82%
feet meters 79%
feet meters 73%
,000 feet meters 70%

14. Siting wind – It really is easy

15. 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.

16. Building Obstructions
Good location for wind turbine
Good location for wind turbine
PREVAILING WIND
Region of Highly Disturbed Flow
Turbulence 2H
Turbulence H
Turbulence 2H
20H
High
Turbulence
Undisturbed upstream wind speed profile 5H
10H
15H
Speed
Decrease
17% 6% 3%
Turbulence
Increase
20% 5% 2%
Wind Power
43% 9%
15H
Turbulence
10H 5H
Appropriate maximum values depend
Upon building shape, terrain and other
Nearby obstacles. 2H
Turbulence

17. 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 wind turbine
WINDWARD
LEEWARD
Good location for wind turbine
Good location for wind turbine
Turbulent
Region H
Turbulent
Region
Turbulent
Region
Wind
Direction 5H
10-15 H

18. 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.

19. Acceleration over a ridge
Crest of Windflow (also region of maximum wind acceleration)
Wind
Speed
Possible High
Turbulence
Crest of Ridge
200%
120%
100%
50%
Wind
Speed

20. Airflow over cliffs
= Turbulence
(A)
(B)
(C)
(D)

21. 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 between mountains)
Zone of high wind velocities
Mountains
Plains
Valley
(B)
Mountains
Prevailing Winds

22. 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

23. Deformation Ratio I II III IV V VI 5-9 8-11 10-13 12-16 14-18 15-21
D = A/B + C/45
Prevailing
Wind
Direction C B A
Deformation Ratio I II
III IV V VI
Probable Mean Annual
Wind Speed Range (MPH)
5-9
8-11
10-13
12-16
14-18
15-21
Source: Data prepared by E.W. Hewson, J.E. Wade, and R.W. Baker of Oregon State University.

24. Griggs-Putnam Index MPH 7-9 9-11 11-13 13-16 15-18 16-21 22+ m/s 3-4
Prevailing Wind I II
III IV V VI
VII
No Deformity
Brush and Slight
Flagging
Slight
Flagging
Moderate
Flagging
Complete
Flagging
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 II
III IV V VI
VII
MPH
7-9
9-11
11-13
13-16
15-18
16-21
22+
m/s
3-4
4-5
5-6
6-7
7-8
8-9
10+
Km/h
11-14
14-18
18-21
21-25
25-29
29-32
36+

25. Siting with no vegetation
If your customer can fly a flag,
they can run wind turbine!

26. In a nutshell – it is just common sense
Know your wind speed average
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