The total diameter of the windmill is 9 feet. It is designed to be a work horse in light (5 to 25) MPH winds. This is the most efficient windmill design based on a NASA study.  High speed 3 blade designs, buy them here, (https://www.magnet4sale.com/xcart4/home.php?cat=302) allow 90% of the energy to pass between the blades and need 20 mph or more to operate, but the TSR (tip speed ratio) can be up around 6 (6 X the wind speed) creating high RPMs to drive a PMA directly.

This windmill is designed to turn at 70 RPM in a 20 MPH wind producing about 1.0 HP which drives a permanent magnet alternator at its preferred 1000 RPM buy means of a hydraulic pump and a hydraulic motor, or a direct drive air compressor or a water pump. A PMA starts generating at about 200 RPM. PMA's increase torque load as RPM goes up. 1.0 HP at 1000 RPM will produce about 687 watts with the right PMA. Car alternators don't work in this application. Learn more at www.windstuffnow.com.  Buy Windpower Workshop by Hugh Piggott.

Most utilities will allow you to spin your meter back during wind conditions so that you can break even at the end of the year. You will still need batteries and an inverter that sync's to the line frequency. If you want to heat water, you will still need batteries because heating elements are designed for a specific power (volts x amps).  Windmill power changes up and down constantly.