On 12 Feb, 21:51, "Arthur2" wrote:

All wind turbines seem to be blades mounted vertically on a horizontal
axle/axis.
These can only be 100% efficient if the wind blows directly onto the face of
the blades.

That's why they can be trimmed into the wind

Or indeed out of it, as one way to survive over-strong winds.

Vertical axis machines have much lower efficiencies in comparision.
They're getting better, and in gusty, crowded urban settings they
might even have the advantage.