over two decades ago I attended a presentation at the Royal Institute, discussing the efficiency of wind turbines, where it was pointed out that for ultimate efficiency, the turbine would have to draw all kinetic energy from the wind, leaving it motionless at the trailing edge. Of course, if you do that, the incoming air mass can't go anywhere so stall the turbine. Therefore, some KE has got to be left to escape.
Unfortunately, this trailing vortex/turbulent wind leaving the trailing edge and moving onto the next turbine makes the KE extracted even less efficient.
So, if this discussion has only been going on for the last few years, and only become open knowledge now, what have those Harvard types being doing for the last decade? Pumping their trust fund students?