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41 in.

The Hula Hoop. Used for Fun and Exercise Since 500 B.C. Helps to Explain Wind Power Concepts

The Cross Sectional Area of a Hula Hoop is a Little Less Than 1 Square Meter

• Face the Hula Hoop toward the bright sun, and the solar power passing through it is about 1000 Watts), or

• 1 kilowatt per square meter.

• 1 kilowatt per square meter is the standard sun intensity by which solar panels are tested. Your electrical harvest is 14% of this.

Hula Hoop

1 square meter

SUN

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Now, Face the Hula Hoop Toward the Wind

The wind power flowing through the Hula Hoop increases dramatically with wind speed (varies by the cube)

Wind Speed Power Through Hula Hoop

8 mph 29 Watts

10 mph 55 Watts

20 mph 428 Watts

28 mph Approx. 1000 Watts

Hula Hoop

1 square meter

“Cut-in” speed

Generator is at rated output power

Same 1000 Watts as solar, but you harvest 40% instead of 14%

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Wind Speed is Higher Above Ground

Even a modest increase in wind speed produces an impressive increase in wind power

Ground

Example. Measured at 30 feet,10 mph 55 Watts per

square meter

Up here at 213 feetwill be 13.2 mph

126 Watts per square meter

At top, 15.1 mph, 153 Watts per square meter

331 feet

213 feet

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At Rated Wind Speed and Wind Power (1000 Watts per square meter), How Much of the Wind Power Can be Harvested?

331 feetUpstream wind

speed VWind speed is slowed by blades to

one-third of upstream V

Betz Law Says the Theoretical Limit is 60%. Realistic Value is 40%.

The max harvest is when blade tip speed is about 6 times the upstream wind speed.

28 mph * 6 = 168 mph tip speed, and 20 revolutions per minute.

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The First Principle of Wind Turbine Operation, Discovered by Experiments More than 200 Years Ago Is:

“To harvest the maximum power out of the wind, the turbine blade speed (RPM) should be proportional to wind speed”

So, if rated wind speed = 28 mph corresponds to 20 RPM, then

● When wind speed = 20 mph, turbine speed should be 14.3 RPM

● When wind speed = 10 mph, turbine speed should be 7.1 RPM

● When wind speed = 8 mph, turbine speed should be 5.7 RPM

Note: If wind speed is higher than 28 mph, the turbine blades are pitched back to hold generator power at rated 1.5 megawatts, so that turbine speed never exceeds 20 RPM.

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Turbine Placement on West Texas Mesa Top

Prevailing wind direction

The best performers are on the opposite edge of the mesa where turbulence is lowest

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300 ft pad

Prevailing wind direction

800 ft

2500

ft

Wind Farms Usually Have 100 to 150 Wind Turbines

• Each turbine occupies a rectangle of about 50-60 acres

• A 300 foot work area “pad” (about 2 acres) is needed for the cranes to maneuver

• Electric power cables are underground

• Wind farms do not interfere with the ranchers or cattle, and the income from royalties is welcome

• Wind farms are NOT noisy. When standing at the base, they are awe inspiring.

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Mesa Top, King Mountain Wind Farm, McCamey, TX

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10

Some Wind

Big Wind

Load Centers

Some Wind

Big Wind

Load Centers