As you know a Sharp rotor provides more lift but less torque than a horizontal Savonius rotor. The lift of a Magnus rotor depends on its spin ratio (relatively to the wind speed).
I did it. An horizontal polystyrene foam Savonius rotor (a little like the device on the video) which flew like a rotating kite during little time.
True.
Thin sheets of plastic or fabric could be light enough to perhaps compensate for the low efficiency, but the structure to hold this would be heavy, above all when the device scales up. Perhaps said structure could be inflatable balloons (in addition to the central beam of the Savonius rotor) settled at each end (and providing some additional Magnus effect taken from the power of the Savonius rotor), the Savonius rotor being settled in the middle, a little like this but by replacing the Darrieus rotor in the middle with a Savonius rotor, then using bottles of constant diameter to hold the rotor as on the sketch on Flettner balloon and VAWT side by side - #4 by PierreB.
As the Savonius rotor is already not very efficient, especially in a more or less flexible version, and it takes energy to stay in flight, we should not expect great results from the generator.