Five times more power.
The Kh2.0 diffuser has achieved what is believed to be a record wind speed augmentation factor of 1.71 which equates by the cube rule to a power increase of 500% compared to an equal diameter open rotor. And then there are the collateral benefits.
An open rotor wind turbine can only extract a maximum of 59% of the wind energy (Betz limit) because above that the wind will simply blow around it rather than through it.
A diffuser breaks this limit as the front of the duct acts like a funnel and entrains the air increasing the forward pressure, while the back acts like a Venturi as air blows past sucking more air from behind the blades reducing the rear pressure. This push and pull increases the pressure differential across the blades from which the power is extracted.
Most of the aerodynamic losses of a turbine are caused by the vortices at the blade tips where high pressure air in front of the blades tries to fill the low pressure space behind them. The duct wall effectively cuts off this air leakage reducing the losses and also the noise.
An aerofoil is at its most efficient lift to drag ratio at one angle of attack (the angle the air hits the blades). Wind speed varies between the top and bottom of a large rotor and also veers rapidly in direction beyond the ability of the rotor system to slew around.
A duct straightens the air flowing through it and thereby mitigates these inefficiencies. Because the wind flows faster through a diffuser than an open rotor, the generator starts rotating sooner and rotates faster.
The higher speed achieved without needing a gearbox improves the efficiency of the generator. For example in a 12 m/s wind a single 3m Kh1.0 turbine will generate > 12.5 kW spinning at ~ 500 rpm. A conventional 6m diameter turbine in the same wind may generate the same power but at < 200 rpm. As generator power is directly proportional to rpm, this literally means the Kh2.0 generator will be less than a third of the size and cost. The Kh2.0 axial flux generator weighs 40kg while for example the Ginlong industry standard open rotor 7.5 kW generator weighs 180kg.
Test conducted and verified by Cranfield University, UK.