Calculate the rotor swept area of your wind turbine. Divide the diameter by two. Find the square of the result and multiply by pi. For example, 6 meters divided by 3 equals 3, which equals 9 when squared. Nine times pi equals approximately 28.26 meters squared.
Locate the average wind speed for your location. Contact the local meteorological society for yearly averages. Record the speed in meters per second. Multiply miles per hour by 0.44704 to convert to meters per second. Energy production is rated in kilowatt-hours, a unit related to meters.
Find the cube of the average wind speed for your location. Divide the result by two. Multiply by the rotor swept area and the air density. Consult your local meteorological society for an exact air density measurement. For example, if the average wind speed is 6 meters per second (approximately 13.5 miles per hour) and the rotor swept area is 28.26 meters squared, then the equation would look like this: 1.2 (average air density at sea level in kilograms per cubic meter) times 28.26 times 108 equals 3,662.5 watts.
Multiply the result by the efficiency rating of the turbine. Locate the efficiency rating from the manufacturer's specifications. For example, if the efficiency rating is 35 percent, then multiply 3,662.5 watts by 0.35 to equal 1281.9 watts. Multiply by the number of hours per year the turbine would run to convert to watt-hours. Use 8,750 hours as an approximation for continuous, year-round use.
Divide the result by 1,000 to convert to kilowatt-hours, or kWh, per year. For example, 1,281.9 watts times 8,750 hours equals 11,216,625 watt-hours, or approximately 11,217 kWh per year.