In principle I see no reason, why
this kind of technology wouldn't be
capable of coming to the market
with quite big wind machines.
About this particular company
I know more or less nothing.
I've already earlier referred
Gary Johnson's book here
to point out that Savonius type
wind machines might be much
better than many people think.
Once more from the introduction
of his book:
http://www.eece.ksu.edu//~gjohnson/
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Agreement on the efficiency of the Savonius turbine apparently has finally been reached a half century after its development. Savonius claimed an efficiency of 31 per cent in the wind tunnel and 37 per cent in free air. However, he commented:[10 ] The calculations of Professor Betz gave 20% as the highest theoretical maximum for vertical airwheels, which under the best of circumstances could not produce more than 10% in practical output.
The theoretical and experimental results failed to agree. Unfortunately, Savonius did not specify the shape and size of his turbine well enough for others to try to duplicate his results.
A small unit of approximately 2 m high by 1 m diameter was built and tested at Kansas State University during the period 1932-1938 [6 ]. This unit was destroyed by a high wind, but efficiencies of 35 to 40% were claimed by the researchers. Wind tunnel tests were performed by Sandia on 1.5 m high by 1 m diameter Savonius turbines, with a maximum efficiency measured of 25% for semicircular blades [1 ]. Different blade shapes which were tested at the University of Illinois showed a maximum efficiency of about 35% [5 ]. More Savonius turbines were tested at Kansas State University, with efficiencies reported of about 25% [13,4 ].
It thus appears that the Savonius,if properly designed, has an efficiency nearly as good as the horizontal axis propeller turbine or the Darrieus turbine.
The Savonius turbine therefore holds promise in applications where low to medium technology is required or where the high starting torque is important. A chart of efficiency of five different turbine types is shown in Fig.8. The efficiency or power coefficient varies with the ratio of blade tip speed to wind speed,with the peak value being the number quoted for a comparison of turbines. This will be discussed in more detail in Chapter 4.
It may be noticed that the peak efficiencies of the two bladed propeller, the Darrieus, and the Savonius are all above 30 %, while the American Multiblade and the Dutch windmills peak at about 15 %.These efficiencies indicate that the American Multiblade is not competitive for generating electricity, even though it is almost ideally suited and very competitive for pumping water.
The efficiency curves for the Savonius and the American Multiblade have been known for a long time [6,10]. Unfortunately, the labels on the two curves were accidentally interchanged in some key publication in recent years, with the result that many authors have used an erroneous set of curves in their writing. This historical accident will probably take years to correct.
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So I think that in general VAWT machines
are really interesting.
- Hannu
