A much better design and much more efficient is the Darrieus Rotors.
Darrieus: a vertical axis wind system invented by G. M. Darrieus of France
in l925 (often referred to as the "eggbeater" because of the rotor shape).
http://members.tripod.com/~Andrei_C/ind-eng.html
http://ourworld.compuserve.com/homepages/jemmett/