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| 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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