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41 in.

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

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41 in.

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  1. 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. SUN Hula Hoop 1 square meter

  2. Now, Face the Hula Hoop Toward the Wind Hula Hoop 1 square meter The wind power flowing through the Hula Hoop increases dramatically with wind speed (varies by the cube) “Cut-in” speed Same 1000 Watts as solar, but you harvest 40% instead of 14% Generator is at rated output power

  3. At top, 15.1 mph, 153 Watts per square meter Wind Speed is Higher Above Ground Even a modest increase in wind speed produces an impressive increase in wind power 331 feet 213 feet 126 Watts per square meter Up here at 213 feet will be 13.2 mph Example. Measured at 30 feet,10 mph 55 Watts per square meter Ground

  4. At Rated Wind Speed and Wind Power (1000 Watts per square meter), How Much of the Wind Power Can be Harvested? Betz Law Says the Theoretical Limit is 60%. Realistic Value is 40%. 331 feet Upstream wind speed V Wind speed is slowed by blades to one-third of upstream V 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.

  5. 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.

  6. Turbine Placement on West Texas Mesa Top The best performers are on the opposite edge of the mesa where turbulence is lowest Prevailing wind direction

  7. 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. 2500 ft 300 ft pad 800 ft Prevailing wind direction

  8. Mesa Top, King Mountain Wind Farm, McCamey, TX

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