Friday, 16 January 2015

Wind-farming

Some Australian farms still use metal wind-mills, wind-powered pumps, to drive underwater water to the surface for stock to drink. These are invaluable in the absence of mains power but require constant maintenance – they suffer in the elements, particularly as they age.




While there are some very nice looking wind turbines on the market - promising reasonably high energy production - these come at a very high price. I have wondered how easy/cheap it would be to convert an old bike into a small wind generator – a bike-windmill – and how much power the generator might produce.  I do not propose to use the power for a particular appliance – rather the power will simply be added to a nearby battery bank for general farm use.





For the bike-windmill I have in mind using no components that cannot be found on a normal bike, some galvanised iron roofing and components pulled from an old electrical motor (perhaps an unused kitchen appliance). 

I have resisted the urge to look for prototypes on the net and so have done no research there – if you are here looking for a working prototype, this article contains no advice on what others have done.

Bikes

I am interested in using a bike for a couple of reasons.

Firstly, the front wheel is mounted on a fork that can rotate 360 degrees.  The fork, if fixed on a riser, might provide a sturdy permanent base for the wind vanes and the associated motor.

Secondly, the back wheel has a gear assemblage which, when cut down, could mount a chain to drive an electrical motor, inducing an electric current as a by-product. This moves the motor away from the axle - allowing simple disconnection for maintenance and during high wind events.

Thirdly, the spoke framework of a bike wheel provides lots of possibilities for experimenting with different wind vanes.

There are lots of downsides. It is a tough gig being a windmill. The wheel itself will generate lots of wind resistance - while rigid, it may turn out to generate very small amounts of power.

Frame for the generator





The fork is stripped down and cut from the bike, leaving generous amounts of tubing attached to allow fixture to the wind generator’s final location.  The front wheel is removed, and a new wheel axle, twice the length of the existing back wheel axle is inserted. The back wheel is then installed, this time outside the wheel enclosure with gears closest to the fork, on the outside of the fork as shown in the picture. (Yes, this will create stress, but it also allows flexibility in relation to the power generator and the possibility of larger than wheel sized vanes.)

The installation is then located in place to test different wind vanes. The location and structural support for the installation is a prime safety concern. I live out in the bush and have lots of safe options - installation in an urban location may be problematic.  Risk may include lightning, collapse, blades disengaging, blades hitting other objects and 100 other possibilities.



Wind Vanes

The first wind vane is to hold the spinning wheel into the wind – this is simply achieved with the fork used by a large V shaped vane fixed to the ends of the fork. Any sufficiently large flat surface should suffice.

The second wind vanes are to deflect the wind and thereby spin the wheel.  The intent is that they be a uniform shape and size such that they can easily be clipped to the wheel struts.  The photograph shows cardboard prototypes being used to estimate effective shapes. 


When the wind vanes are confined to the rim of the wheel, the installation has a modest wind catchment area of 3+ sq feet. However, because the wheel is outside the fork frame, the vanes can be much larger, but will continue to benefit from the rigidity of the rim. If the vanes are twice the size of those shown, the wind catchment quadruples to 12+ sq feet. Whether it would be possible to catch this much wind without compromising the vane structure or moving to more expensive material remains a subject of experimentation :)

An array of these - say 10 - 2' blades - will catch about 100 sq feet.  This would be the equivalent of a commercial turbine with 6' blades.

Chain and motor


I have used a simple induction motor from a low voltage appliance, turned by a chain attached to the wheel axle. A simple metal housing for the motor has been removed for the photos.


Assessment

The bike wind generator was assembled in about two hours using the parts noted above. While I originally welded two axles together to get the required length, I replaced that with a single toughened axle on the basis that this was the part that was most likely to fail under pressure. 
The bike windmill immediately pointed into the wind and produced spin and current. In its present form, I expect it to shown signs of wear immediately so, as I get time, the frame and iron parts will be braced. 




A couple of different vane designs are now being tried. This page will be updated to include information about different vanes and power production against different wind speeds.

Peter Quinton
Palerang
January 2014





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