Electricity Windmill - A Home Power Wind Generator Conversion Outlined
The following article provides an outline for converting a conventional water-pumping windmill into one that produces electricity. The outcome is a robust, low tech wind generator well suited to self sufficient living off the grid.
Millions of windmills have been built over the years to pump water on farms. Thousands of these windmills now stand abandoned in fields.
They can often be bought on the cheap and with conversion produce a cost effective wind generator to provide electricity. Windmills originally designed to pump water are relatively inefficient but offer advantages over other styles of wind generator in areas considered too calm for conventional (propeller type) wind turbines.
Unlike modern wind turbines specifically designed for the production of electricity, windmills for pumping water have a high "solidity" ratio (ratio of blade area to swept area) which give much greater torque at very low RPM. Higher torque translates into a machine that will produce electricity from very low speed winds. Due to the low RPM the machine requires gearing to achieve high enough RPM at the alternator to generate electricity.
All this of course implies low efficiency. And yes the "electricity windmill" outlined here is "inefficient" but it's also very effective! The unit was part of a combination solar wind power system and while it provided a mere 1000 Watt maximum output in a stiff breeze the low start-up speed means it produced significant power in low wind situations.
The original discarded windmill was purchased for $600. It's a 14' Comet 3 windmill on a 40' tower. The differential was 6:1 ratio from Austin 6 ton truck ($250). Flange mounted on the differential pinion shaft was a fabricated 600 mm pulley wheel around which ran 2 long series v belts driving a standard 24 volt 35 Amp truck alternator ($200). The original hub of the "fan" disc was replaced by a steel fabricated hub which bolted directly onto the Austin truck axle where the wheel would have been. The differential gears were disabled by welding them together which allowed the differential to act as a simple right angle gearbox.
The final ratio for step up RPM was around 75:1 - Maximum RPM of the "fan" was about 100 RPM giving around 7000 alternator RPM at maximum speed.
Significant rebuilding of the windmill head and stem was required. The original iron casting designed for reciprocating action applied to the pump rods was replaced with a new fabricated steel stem and head on which was mounted the truck differential and original tail mechanism. The only critical aspect was to maintain the original offset of the "fan" shaft from the centre of rotation of the entire windmill head - the offset is to ensure that the windmill folds (yaws) in high wind to protect the mill from over-speed.
The performance of this crude wind generator was in reality quite amazing - in conjunction with a 600 Watt solar array we were energy self sufficient in a home with all mod cons including an electric refrigerator. The "electricity windmill" provided 7 years of trouble free service until it was taken out of service after connection to the grid. As it turned out the windmill and solar array for our stand alone home power system proved to be a remarkably good renewable energy investment.