The basics of wind energy and recommendations to installing

Small Wind Systems

Southwest Windpower, Inc.

Wind is a form of Solar Energy

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.

RERADIATED HEAT82,000

ABSORBED120,000

GEOTHERMAL GEOTHERMAL HEAT 30HEAT 30

SOLAR RADIATION178,000

PHOTOSYNTHESIS100

TIDES 3

HEAT FROM EVAPORATION40,000

REFLECTED TO SPACE53,000

KINETIC ENERGY350

The details of wind

Important information about wind energy that you really don’t need to

worry about but is good to know

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

Wind speed -and- Potential Energy

Power in 1 m2 at a wind speed of 3 m/s:

0.5 x 1.204 x 3.14 x 12 x 33 = 51 W

Power in 1 m2 at a wind speed of 5 m/s

0.5 x 1.204 x 3.14 x 12 x 53 = 236 W

Energy Available in the wind follows the equation

½ (air pressure) x 3.14 (pi) x (blade length)2 x (wind velocity)3

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

Power in 1 m2 at a wind speed of 4 m/s:

0.5 x 1.204 x 3.14 x 12 x 43 = 121 W

Power in 1 m2 at a wind speed of 8 m/s

0.5 x 1.204 x 3.14 x 12 x 83 = 968 W

Energy Available in the wind follows the equation

½ (air pressure) x 3.14 (pi) x (blade length)2 x (wind velocity)3

Every time wind velocity doubles, available energy increases 8 times!

Swept Area -and- Potential Energy

Power in 1 m2 at a wind speed of 5 m/s:

0.5 x 1.204 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 1.204 x 3.14 x 1.52 x 53 = 532 W

Swept Area is the best way to determine TurbinePerformance at normal wind speeds (sub 18 mph avg.)

How does Swept Area affect Potential Energy? How does a 1 m blade compare with a 1.5 m blade?

[Keep this fact in mind when comparing the Whisper H40 with the Whisper H80!]

Betz LimitThe 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 58 W 98 W H40 31% 80 W 154 W 260 W H80 28% 150 W 314 W 531 W 175 35% 420 W 706 W 1196 W

Weibull Distribution

From Hybrid Power Design Handbook, by C.D. Barley

WIND SPEED AVERAGE IN METERS PER SECOND – M/S

Fre

quen

cy a

t whi

ch th

e w

ind

blow

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 moreenergy because of the greater occurrences of 10+ m/s velocities.

Roughness for flat terrain

Roughness Wind shearexponent

Water or ice 0.1

Low grass or steppe 0.14

Rural with obstacles 0.2

Suburb and woodlands 0.25

Wind speed change with height

surface10

12.2

12.9

13.5

HEIGHT WINDSPEED (ft) (mph)

0

30

60

90

V = Vo(H/Ho)

Tall towers matter – each 30 foot increase in height will result in another 25% Energy Output!

The Details in Wind

Elevation Tower height Wind speed average

Important information about wind energy that you really do need to know

ElevationAltitude: Density decreases with altitude

Output compared to power curve

1-500 feet 1-150 meters 100%

500-1000 feet 150-300 meters 97%

1000-2000 feet 300-600 meters 94%

2000-3000 feet 600-900 meters 91%

3000-4000 feet 900-1200 meters 88%

4000-5000 feet 1200-1500 meters 85%

5000-6000 feet 1500-1800 meters 82%

7000-8000 feet 2100-2400 meters 79%

8000-9000 feet 2400-2700 meters 73%

9000-10,000 feet 2700-3000 meters 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

H

Region of Highly Disturbed Flow

2H

2H 20H

PREVAILING WIND

Undisturbed upstream wind speed profile

5H10H

15H

HighTurbulence

5H 10H 15H

Speed

Decrease17% 6% 3%

Turbulence

Increase20% 5% 2%

Wind Power

Decrease43% 17% 9%

Appropriate maximum values depend Upon building shape, terrain and other Nearby obstacles.

Good location for wind turbine

Good location for wind turbine

Turbulence Turbulence

Turbulence

Turbulence

Turbulence2H

5H 10-15 H

H

WINDWARD LEEWARD

Turbulent Region

Turbulent Region

Turbulent Region

Wind Direction

The region underneath the curve has too much turbulence, and is not a good site to install a wind turbine. ThisRegion is determined by the height (H) of the tallest tree. The region with the straight, smooth lines ABOVE theCurve has air flow that is laminar, free flowing, which is IDEAL for a wind turbine.

Good location for wind turbine

Good location for wind turbine

Good location for wind turbine

Siting behind a row of trees

Streamers and turbulenceTop of barrier-induced turbulence

TurbulentFlow

Smooth Flow(Good height to install a Southwest Windpower Turbine)

By using a kite and adding streamers to the line you can determine the area behind treesor buildings where turbulence is present. The areawith smooth air flow will have a straight streamer asopposed to turbulent streamers that are flappingconstantly.

Predominant wind direction

Kite

Acceleration over a ridge

100% 50%

120%200%

Possible HighTurbulence

Crest of Ridge

Crest of Windflow (also region of maximum wind acceleration)

WindSpeed

WindSpeed

Airflow over cliffs

(A)

(C)

(D)

(B)

= Turbulence

Valleys between mountainsZone of accelerated air flow

Prevailingwinds

Mountains

Mountains

Plains

(A)

(B)

Zone of high wind velocities

Valley

Mountains

Plains

Prevailing Winds

Plains

Valleys can be areas of high wind speeds when winds are funneled and accelerated because of

the topography (valleys between mountains)

Mountains

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 RatioD = A/B + C/45

PrevailingWind Direction B A

C

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.

Griggs-Putnam IndexPrevailing Wind

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+

0 I II III IV V VI VIINo Deformity Brush and Slight

FlaggingSlight

FlaggingModerateFlagging

CompleteFlagging

PartialThrowing

CompleteThrowing

Carpeting

Siting with no vegetationObservations 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 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