Is there a formula for determining the amount of energy produced via a windmill?

Hey TK, good question. Actually, it isn't that difficult to get into. There are basically four things that figure into the power output of a wind turbine.

1. Swept area of the blades

2. Density of the air

3. Efficiency of the turbine design

4. Velocity of the wind

P = .5 X rho X Cp X A X V3

P is power in watts, .5 is a constant, rho is the air density, Cp is the efficiency of the turbine and V3 is the velocity of the wind cubed. This is why airspeed is such a determining factor in wind turbine design. The .5 constant is constant by design, the efficiency is whatever the manufacturer can pull off in design and construction, the area of the blade sweep is fixed at construction, so only the airspeed varies, and since you cube the value of the speed, if the wind speed increases from 10 to 30 miles an hour for example, the turbine now has to convert 27 times as much energy.

We have a small turbine at our place that's been running for almost 10 years now. It is a 3 blade model, designed for higher winds. A two blade unit is more efficient, but if you live in a higher wind area like we do, efficiency is not so important. Even with our small unit, a 25 mile per hour day allows our little 7 foot diameter unit to run the entire home and add a small charge to the batteries at the same time.

If you want to learn more, skip wikipedia and go to the experts. The American Wind Energy Association is a non profit group that works only with wind power issues. The two gurus in the business are probably Paul Gipe, who has written a book, "Wind Power for Home and Business," and Mick Sagrillo who has been running his own business in wind power for 30 years and has authored several papers and articles. To get straight to the source, google, "Wind Turbine Power Equation," and look for a link to an AWEA website for an explanation of the formula. I will list a few other sources below as well. Good luck, and take care, Rudydoo

It's a complicated bit of math. The references go into it a bit, and there are lots of others that go into a lot more detail.

But with no background in this area, the math may not be very meaningful.

Perhaps you should just state what info you are looking for?

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Yes. I saw a few in basic fluid mechanics handbook. I do not remember it but check the local library.