How to Calculate the Amount of Wind Generated Energy for Home Use

Windmills harness the wind to generate electricity.

Calculate the amount of electrical energy produced for your home by your windmill by making a few measurements and performing a few calculations. Windmills convert the mechanical energy of the blowing wind into electrical power. The power output potential of a residential windmill depends on the wind speed in your neighborhood, the length of the blades and how efficiently the device converts available wind energy into electrical power. Efficiency of a windmill depends on the specific blade design.

Things You'll Need

• Tape measure
• Calculator

Instructions

1. Determine the average wind speed in miles per hour in your neighborhood by consulting a local weather forecast 300 days in a row, adding all the speeds together and dividing by 300. For example, say the average wind speed in your area is 12 miles per hour.

2. Convert the average wind speed to meters per second by division by 2.237, since 1 meter per second equals 2.237 miles per hour. This is done because equations in science are expressed in metric units. Continuing the example, you have 12 miles per hour divided by 2.237 yielding an average speed of 5.36 meters per second.

3. 

   Utilize a tape measure to determine blade length.

   Measure the length of one of the blades in meters, measuring from the center of the windmill to the edge of the blade. For example, you might have a windmill with blade length of 1.5 meters.

4. Multiply the square of the blade length by 1.88 kilograms per cubic meter. The quantity expresses the density of air, as well as a geometrical factor representing the cross-section of air the windmill blades harness. Performing this operation leads to (1.5 meter)^2 times 1.88 kilograms per cubic meter, or 4.23 kilograms per meter. The symbol "^" represents an exponent.

5. Multiply by the cube of the average wind speed and by the efficiency of the windmill design designated by the manufacturer to obtain the power output in watts. Assume for the sake of calculation the windmill design is that of the three-blade rotary type with an efficiency of 30 percent. Completing this step leads you to 4.23 kilograms per meter times (5.36 meters per second )^3 times 0.30, or 195.4 watts. In the last step, you employ the fact that a watt equals a kilogram times a meter^2 per second^3.

6. Calculate the energy in joules generated by the windmill per month by multiplying by 30 then 24 followed by 3600, since a month is approximately 30 days, a day contains 24 hours and an hour contains 3600 seconds. A watt is the same as a joule per second, so multiplying by time yields energy. Performing this step leads to 195.4 times 30 times 24 times 3600 or 5.1 x 10^8 joules.

7. Convert the energy generated to the kilowatt-hour, the standard energy unit used by the electric company, by dividing by 3.6 x 10^6, since a kilowatt-hour equals 3.6 x 10^6 joules. Completing the calculation brings you to 5.1 x 10^8 joules divided by 3.6 x 10^6 kilowatt-hours per joule, which is 142 kilowatt-hours of energy generated per month.

References

• "Physics for Scientists and Engineers with Modern Physics"; Raymond A. Serway and John W. Jewett; 2009
• Engineering Tool Box: Speed
• University of Oregon Physics Department: Wind Energy
• Engineering Tool Box: Power
• Engineering Tool Box: Energy

Resources

• U.S. Energy Information Administration: Frequently Asked Questions About Electricity