The Savonius Super Rotor !
(Page 3 of 4)
March/April 1974
By Michael Hackleman
Finally, there's still a further feature of the Savonius unit which isn't apparent to the eye, but which has shown up in preliminary tests of Earthmind's prototype: The S-rotor can begin to charge 12volt batteries at wind speeds lower than the 7-mph minimum required by the "normal" prop-driven plant. Our installation has worked successfully at 6 mph, and we believe that some modification of the rotor will lower the necessary speed to 5 mph. We're continuing our research into this possibility for the benefit of people who live in areas of low average wind speed and who may not be able to use systems of the Stuart mill type.
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We've adapted our design to the other extreme, too, by installing a centrifugally operated spoiler to slow the rotation of an S-rotor in very high wind speeds A separate sensor (also mechanical) is used to limit or switch off field current to the alternator in case of either very high winds or no winds at all.
Our test results from the prototype S-rotor were so encouraging that we've recently built a much bigger unit from three 55-gallon drums. We're evaluating the performance of both versions with the help of a data collection system which is automatically activated by a sensor any time the wind speed exceeds 3 mph. Our test equipment also records information from a separate wind velocity and direction indicator. With the aid of our data recorders we've assembled some figures to show what kind of power the Savonius rotor can produce. Such a windplant's capacity, of course, depends a good deal on your choice of alternator, so I'm listing our results for units with three ratings: a 45-amp (very common), 60-amp (a little harder to locate but there if you really look) and a 130-amp (which can be found in commercial vehicles or in passenger autos like the Cadillac El Dorado). I've included the peak output the plants can provide, and the normal power you can expect if you live in an area of, say, 8 mph average annual wind speed Data is given for both our prototype S-rotor and for our big new unit.
If you're wondering why the large S-rotor has such a high power output, the answer is that we've hooked four alternators to it. Two would normally be sufficient, but we've added two more as brakes. This way, when normal wind devices would have to shut down because of dangerously high wind speeds, our unit can keep right on going to take as much energy as the rushing mass of air can provide.
The price of all that power is surprisingly low. Since the S-rotor can be built from readily accessible materials, its cost will almost always be less than $100 (not including batteries or inverter. The latter, if required, is the same kind used in a conventional system.) We intentionally purchased all the parts that went into our prototype-alternator, gears
and chain, bearings, pipe, stock rod, screws, bolts, eyebolts, guy wire, turnbuckles, paint and stain (plus miscellaneous springs, wire, etc.)-and spent only $103. Our second, larger rotor cost less than half as much because we already had most of the necessary parts all but the bearings, gears and chain.
