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How Much Energy Will Wind Turbine Generate?

Relative size
According to the AWEA Small Wind Turbine Performance and Safety Standard, the Rated Annual Energy of a wind turbine for home is the calculated total energy that would be produced during a 1-year period with an average wind speed of 5 meters/second (m/s, or 11.2 mph). The following formula illustrates factors that are important to the performance of a wind turbine. Notice that the wind speed (V) has an exponent of 3 applied to it. This means that even a small increase in wind speed results in a large increase in power. That is why a taller tower will increase the productivity of any wind turbine by giving it access to higher wind speeds.

The formula for calculating the power from a wind turbine is:
  • Power = Cp 1/2 ρ A V³
  • P = Power output, watts
  • Cp = Maximum power coefficient, ranging from 0.25 to 0.45, dimension less (theoretical maximum = 0.59)
  • ρ = Air density, kg/m³
  • A = Rotor swept area, m² or
  • π D² / 4 (D is the rotor diameter in m, π = 3.1416)
  • V = Wind speed, mps
The rotor-swept area (A) is important because the rotor captures the wind energy. So the larger the rotor, the more energy it can capture. The air density, ρ, changes slightly with air temperature and with elevation. The ratings for wind turbines are based on standard conditions of 59° F (15° C) at sea level. A density correction should be made for higher elevations as shown in the Air Density Change with Elevation graph. A correction for temperature is typically not needed for predicting the long-term performance of a wind turbine.
Air density change

Although the calculation of wind power illustrates important features about wind turbines, the best measure of wind turbine performance is annual energy output. The difference between power and energy is that power (kilowatts [kW]) is the rate at which electricity is consumed while energy (kilowatt-hours [kWh]) is the quantity consumed. An estimate of the annual energy output from your wind turbine, kWh/year, is the best way to determine whether a particular wind turbine and tower will produce enough electricity to meet your needs. 

Contact a wind turbine manufacturer, a dealer/installer, or a site assessor to help you estimate the energy production you can expect. They will use a calculation based on the particular wind turbine power curve, the average annual wind speed at your site, the height of the tower that you plan to use, micro-siting characteristics of your site and, if available, the frequency distribution of the wind (an estimate of the number of hours that the wind will blow at each speed during an average year). They should also adjust this calculation for the elevation of your site.

To get a preliminary estimate of the performance of a particular wind turbine, use the formula below:
  • AEO = 0.01328 D² V
  • AEO = Annual energy output, kWh/year
  • D = Rotor diameter, feet
  • V = Annual average wind speed, mph
Before purchasing a household wind energy generation system, please calculate the power generation capacity of the system according to the formula, and consider the number of years of power generation, the economic cost, and the strength of the wind in your location. If it brings you even less than the cost, then wind power is not recommended for you.

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