Let’s say more than 20 m/s. Today I experimented an arodynamic toy inside the 42 cm tire inner tube, with strong winds from 8 m/s to 12 m/s and more, at 1 m height, that to try to approach the shape of S1500. As expected the tire accelerated the flow. The toy inside the tire did not appear to change appreciably from the tire alone, either way.
But the shape of S1500 can perhaps be more efficient (than the experimented toy inside the tire), because the air seems to be progressively ducted by the shape of the central airship, and towards the inner part of the ring of the turbines, while the outer part is also ducted.
So, S1500 deserves in-depth analysis, because it could be a real step forward, even if we must remain critical: how long can very light wind turbines last when subjected to regular strong winds?