Power Extraction By Windmills

These calculations run in your web browser, using embedded Javascripts; which means that you must set your browser to allow Javascripts .

This is a very complex topic and there is lots of stuff on the internet about this; but here is a quick look at extracting power from the wind.

The efficiency of windmills is largely driven by:

  • If there are only a few blades, most of the air passes between the blades and does nothing. Look at the windmill from the front, not the side.... the blades don't get hit by a lot of the air.
  • If there are too many blades, the air goes around the windmill instead of through it.
  • Gear train and generator efficiencies.

    • In the calculator below you simply punch in any efficiency number you like..... but of course, we're bypassing a lot of the unknowns by doing that.

    Refer to:
  • Text example 2-2, page 59. However note that in part (c), that is POWER (kW) and not ENERGY (kW-hours)
  • Text example 3-10, page 139 for using the Ideal Gas Law to calculate density of air.
  • Text equation 2-8 to calculate mass flow rate.

    •

    Also, lets define windmill efficiency, n = (power out) / (available wind power). So that (power out) = n * (available wind power).
    The "available wind power" term, as used here, refers to the power in the entire streamtube of air that passes through the windmill diameter, not just the air that directly hits the individual blades.

    Input
    Diameter (m)
    Wind Velocity (m/s)
    Air Pressure (kPa)
    Air Temperature (deg C)
    Windmill Efficiency, n
    Power Available (kW)
    Power Output (kW)
    Air Mass Flow (kg / s)
    Air Density (kg / m3)