The savonius wind turbine is not very efficient at capturing wind energy; you would need a rotor 29 ft tall to generate the same amount of energy as a conventional prop with a radius of 7.8 ft.
ILLUSTRATION: MOTHER EARTH NEWS STAFF
MOTHER EARTH NEWS has received several letters indicating that the amount of power we reported would be available from our savonius wind turbine ("The Savonius Super Rotor!") was much higher than is actually possible with this type of unit.
With the kind assistance of William Vance, Advanced Concepts Division of Science Applications, Inc., La Jolla, California, and with the aid of Mark's Mechanical Engineer's Handbook, we have calculated values for the amount of power produced by the turbine or S-rotor. You may check our equations yourself in here in our document titled Savonius Super Rotor.
In general, the S-rotor appears convenient for situations with smaller power requirements where its size is manageable... Elektro GmbH of Switzerland produces a 250-watt and a 500-watt model, but uses the familiar three-bladed Stuart for higher-powered models, 1,000 watts and up. But any situation is unique in its wind characteristics, power requirements, topography, and available materials and skills, and each factor should be considered in deciding the best wind plant to erect.