Since towers are only 25% efficient that makes the horizontal ones only about 18% efficient. By that metric, why bother? Besides the higher costs to manufacture, the power needed to make the component parts likely exceeds the lifetime power generation of the unit before failure.
No the Spanish enclosed versions are 25 per cent less efficient per given wind velocity and flow versus the exposed tower turbine blades....Yes you’d need a higher minimum speed to get them turning but once turning and brought up to speed, you have energy flow similar to the open 3 blade monsters.
The enclosed are more durable and don’t break down as frequently. They are more protected from the elements other than the wind. So the 25 per cent less efficiency start up speed is more than made up for by the savings in not having to repair or replace them as frequently. The turbine design is different...more like jet turbines, smaller blades at top and larger at bottom.