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Last Updated on:
06/25/2015 06:30 AM 
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. 





 