hey guys, my first post here
i just wanted to share an idea with you, since the article mentioned VAWT's ... specifically it is about the Savonius turbine, even though it was dismissed by the article
there has been talk about how to increase the efficiency of the Savonius rotor, and one of the ideas mentioned was to put a shroud on the retreating side , but this practically turns it into an inefficient horizontal axis wind turbine
but then i had a thought, what happens if you have some Darreius blades surrounding the Savonius rotors, but be in such a close proximity that the 'downwash' from the Darreius blades will nullify some of the wind going against the Savonius's retreating side? the blades would not have a normal Darreius aerofoil profile since they have to account for the effect of the Savonius rotor on the airflow, specifically the side which is facing away from the wind will probably not get any lift, so the blades will have to work at even more oblique angles of attack than they already are in a plain Darreius turbine
in all likelihood this may not be a breakthrough in wind turbine efficiency, but i have always believed that different wind turbines are suited for different 'wind regimes' , HAWT's for wind tunnel-perfect air, Darreius's for slightly less steady air, and Savonius for scavenging whatever wind energy you could when you absolutely need it... so i think that a VAWT like mine can serve the gap in which the wind is too fast for a simple Savonius turbine to be efficient, yet too slow for Darreius blades alone...
this is distinct from having a VAWT with practically independent Savonius and Darreius sections, either because they are placed one above the other since the Savonius turbine will simply be a load for the Darreius blades unless you use a one way bearing, or because the Savonius rotor has negligible diameter compared to the Darreius blades which would nullify the low windspeed-capturing property of the Savonius rotor (that, or have the Darreius blades be of such large diameter that it is pushing the definition of 'small wind turbine' ) ; i believe that the interaction between the Savonius and Darreius rotors can be taken advantage of to create a better wind turbine
::edit:: actually, if you apply Newton's 'every action has an equal and opposite reaction' law, it would become apparent that the downwash coming from the Darreius rotors would divert the wind in a rotation opposite of the Darreius rotor
hence, the Savonius rotor would have to rotate in the opposite direction of the Darreius in order to take advantage of the downwash... depending on the cost and availability of coaxial contra rotating gearsets, it may make a viable option for VAWT's to perform at levels closer to HAWT's