This post proposes to increase the efficiency of a VAWT with yawing shields. In the case of the Darrieus, for example, the drag on the blade as it travels in the upwind direction is reduced by diverting the flow with a shield. The flow that is not diverted is slowed because the channel becomes wider in the middle. The flow on the opposite side of the rotor (left side in the diagram below) is not manipulated because it is already in the direction of blade velocity, and it therefore already reduces drag. As for the Savonius, I’m not sure if the idea will work, but I’ve drawn my best guess at how to augment the efficiency of the turbine using either one or two shields.