An alternative turbine design
The Savonius rotor is a popular means of generating small amounts of wind power to run small motors, water pumps, or other electrical equipment at remote unmanned sites. It is popular because it is easy to build, and inexpensive to maintain.
Although it is considered to have been invented by Sigurd Savonius as an alternative to the vertical windmill rotor, it was a variation of a medieval turbine design - Savonius patented it in 1929. There has been increased interest in the design recently as the trend toward renewable power sources has grown, as it is fairly easy for amateurs to design and build one.
It has to be said that it is not the most efficient means of electricity generation, as the weight of the rotor, the high starting torque and high drag makes it less efficient than the more conventional 'propeller' turbine, which is preferred in large-scale and commercial applications.
On the positive side, the ease of construction, coupled with inexpensive material requirements makes it ideal for the DIY enthusiast keen on having environmentally friendly aeolian energy available. The major disadvantage, that it takes some power to get going, is easily overcome. Many people simply give it a push to start it!
So, what does it look like?
Imagine a closed hollow cylinder - an oil drum will do. Cut it in half down its centre, and arrange the two halves on a platform. The two halves may be joined in the centre to give a stronger rotor, as in the first diagram below, or with a gap between, which is not as strong, but more efficient. The wind blows through the whole contraption, creating a simple, if crude wind turbine.
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Whichever design is used, the remainder of the generator is straightfoward. A bearing is attached to the base of the rotor, which drives a dynamo or alternator. With some care given to the construction, they need not look like a Heath Robinson creation - there are subtle design variations, but the principle always remains the same. Many of these generators are demonstrated and used at the Centre for Alternative Technology at Machynlleth in Wales. A java simulator is also available at http://www.picoturbine.com/rotorsim.htm, which demonstrates the drag and turbulence from a Savonius rotor in use.
http://www.cat.org.uk/
://www.angelfire.com/ak/egel/savonius.html
http://www.southcom.com.au/~windmill/
Encyclopædia Britannica
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