The power available from the wind varies as the cube of the wind speed, or Cube Rule. If the wind speed doubles, the power of the wind increases 8 times. For example, a 10 mile per hour wind has one eighth the power of a 20 mile per hour wind (10 x 10 x 10 = 1000 versus 20 x 20 x 20 = 8000). One of the effects of the Cube Rule is that a site which has an average wind speed reflecting wide swings from very low to very high velocity, may have twice or more the energy potential of a site with the same average wind speed, which experiences little variation. This is because the occasional high wind packs a lot of power into a short period of time. Of course, it is important that this occasional high wind comes often enough to keep the batteries charged. If you are trying to provide smaller amounts of power consistently, use a generator that operates effectively at slower wind velocities. The following table will give you an idea of the power, in kilowatts, that is available from various wind turbine sizes at different wind speeds.