Ian_m wrote:

This subject has been on my mind for the past 2 days.
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.

Can never be 100% efficient. or else you would be left with still air
behind the blades, thus blocking the incoming. Usually significantly
less the 50% efficeincy to allow the air after the blades to have some
energy left to carry it away.

around 1-5% actually.

If you take the actual kinetic energy of teh whole wind mass up[ to the
blade tip hight over the windfarm area.

If it were 50% the windmills downwind would stop turning.