drag type VAWT are very limitted on the speed. They can not move faster than the wind... resulting in the low TSR. A lift type VAWT can have a higher RPM as it can go faster than the wind (like a VAWT), but has a poor start-up speed. A combination is best really for the DIY. It also sounds like those numbers are for HAWT and likely will not give you as accurate of numbers. VAWT have a larger surface area than what the the area covered for a HAWT has. and depending on the design, you can get a power stroke out of 25 to 75% of the stroke depending on design.
It just can not take into acount design differences like...
http://www.youtube.com/watch?v=Uj2c4NreTSY&feature=related
http://www.youtube.com/watch?v=dl6m4emdeBI
http://www.youtube.com/watch?v=q7ffNWkefyY&feature=related
http://www.youtube.com/watch?v=8FbiPI1iYSk&feature=related
http://www.youtube.com/watch?v=CZ1KN0fKqyA&feature=related
http://www.youtube.com/watch?v=RPN_oZf1DSc&feature=related
http://www.youtube.com/watch?v=UdoKEYNfoVE&feature=related
http://www.youtube.com/watch?v=q9flSPAdOLk&feature=related
http://www.youtube.com/watch?v=CkIX3_O8sWg&feature=related
http://www.youtube.com/watch?v=ZXYUBNpa4Hg
These are a wide range of designs, ranging from about half the size of yours up to probably 2 times. Not all give ratings, but some say from 500w to 5kw. Now the Lenz type do not seem to be the best of the ones I show above, but you might be able to get a 1Kw if you can gear up your generator as the speed of 91mph at 20mph wind is actually probably a bit high. For VAWT they lower the diameter the higher the RPM for drag types.
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