My brother has been working on some VAWT designs. He is doing it as a test project, not a working design. He does not report large amounts of power available, but his VAWT is on the ground so he can test different blades, so efficiency is low. However he has been trying a lot of different designs and is improving efficiency and buildability as he goes.
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The latest thing he is working on is a Kline-Fogleman airfoil. This is significant because one could use easily use the wonder material of the future to build airfoils: coroplast.
Kline Fogleman airfoil - Wikipedia, the free encyclopedia
In particular KFm-3 looks like an easy to build airfoil with coroplast. There could be some heat applied to the coroplast to bend it as well (as in KFm-5A), to try for an even more efficient foil. Bending would also add stiffness to the airfoil.