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Many years ago David Johnson, P.E., helped a local Denver company develop an electronic control circuits for a small wind generator which they were
perfecting. They were fortunate to be near the National Wind Technology Center (NWTC) test site near Boulder, Colorado. They were
able to do much of the testing using NWTC's automated data acquisition system. |
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Wind Basics -- Wind Energy Physics -- Wind Power Equation -- Wind Sail Generator -- Sail Boat Energy Generator
Sail Train Energy Generator -- Sail Truck Energy Generator -- Miscellaneous
Information -- Useful Links |
| Wind Power Equation |
| To predict how much power is available from the wind, you can use the equation below. |
| Power in watts = (collection area in sq. ft.) (Wind speed in MPH)3 (0.0054) |
| To illustrate how this equation works, imagine that you have a wind turbine with a diameter of 10 feet (area of 79 sq. ft) that is spinning in a
steady 30 mph wind. According to the equation above, if the generator were 100% efficient, it would produce about 11,500 watts of electricity. |
| Of course, perfect machine does not exists that can extract all of the available energy. A more realistic efficiency figure is 30%. So, using our
example above, we could expect our generator, in a 30 mph wind to produce about 3,500 watts of electricity. Now, if the wind were to increase to 60 mph, according to the equation, the
power produced would increase by a factor of eight or 28,000 watts. |
| This cube function is what makes control systems for extracting power from the wind so difficult to design. A small change in wind speed
means a large change in electrical power output. |
| In the equation above, note that the electrical power produced is proportional to the wind collection area. So, it is advantageous for a wind farm
to collect as much wind as possible by having large diameter wind turbine propellers. However, conventional wind turbines don't scale very well. As wind turbines become larger, the
cost of the supporting towers and the propellers drives up the cost per kilowatt hour of the energy converted. Large arrays of medium size wind turbines are generally used in wind farms. |
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