This is a fully parametric vertical axis twisted savonius type wind turbine inspired by these commercial turbines http://www.windside.com/
Settable parameters are height, radius, number of segments, wing thickness, hub hole diameter and base thickness. Since each segment is divided in two parts quite big turbines can be printed on a standard fdm printer.
I have included stl files for two different sizes, a small three segment 200x100mm and a giant six segment 840x420mm that still fits a prusa mk2s.
Any other size can be obtained by opening the included FreeCAD source and setting the parameters in the config spreadsheet .
The parts need to be glued together for strength.
Check out this one also: https://www.thingiverse.com/thing:3308280
This one should be more efficient for a given swept area, but the one behind the link might be more efficient for a given amount of plastic (but that is just a guess...).