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How do I Find Horsepower From Wind?

Horsepower is a unit of energy generation per second in the British (not metric) system of engineering units. One horsepower (hp) corresponds to a power of 745.7 watts or joules of energy created each second. The amount of power that a given windmill is capable of producing depends on the local average wind speed in your area as well as the air's density or compactness. Factors specific to the windmill's design effecting power output are its efficienc,y or how well it converts wind energy to electrical energy, and the length of its blades as measured from the center of the windmill.

Things You'll Need

Calculator
Tape measure

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 together all the speeds and dividing by 300. The large number of measurements should average out seasonal variations and unusual wind activity. Suppose for sake of a sample calculation the average wind speed is 13.0 miles per hour.
- 2
  Covert the average wind speed to meters per second by dividing by 2.237, because one meter per second contains 2.237 miles per hour. Performing this step brings you to 13.0 divided by 2.237 or 5.8 meters per second.
- 3
  Calculate the cube of the average wind speed in meters cubed per second cubed. This leads you to 5.8 (meters per second)^3 or 195.1 meters cubed per second cubed. The symbol "^" denotes an exponent and is read as "to the power."
- 4
  
  Use a tape measure for finding distances.
  
  Measure the length in meters of one of the windmill's blades. For example, say the blade length is 1.2 meters.
- 5
  Calculate the circular area in square meters that the blades span by multiplying the number pi (3.14) times the square of the blade length. This is the area of wind that the blades capture as they spin. Performing this computation yields 3.14 times (1.2 meters)^2 or 4.52 square meters.
- 6
  Divide the density of air by two, then multiply the result by the area and the cube of the wind speed to arrive at the theoretical power output in watts for the windmill. Take the density of air to be 1.2 kilograms per cubic meter. Now you have (1.2 kilograms per cubic meter divided by two) times 4.52 square meters times 195.1 meters cubed per second cubed. or 529.1 kilograms times meter squared per second cubed. This is equivalent to 529.1 watts, since a watt is a kilogram times meter squared per second cubed.
- 7
  Multiply the theoretical power by the efficiency of the windmill's design expressed as a decimal to obtain the actual power output. For example, suppose the design is a three bladed rotary windmill with efficiency of 30 percent then the actual power produced is 529.1 watts times 0.30 or 158.7 watts.
- 8
  Convert the actual power created by the windmill to horsepower by dividing by 745.7 to arrive at the power in horsepower units. Finishing the exercise you have 158.7 watts divided by 745.7 watts per horsepower which equals 0.21 horsepower.

Nature