Evaluation of the different types:
Generator with a horizontal axis:

the generators with three wings and horizontal axis, currently used almost exclusively for large generators, requiring a complex regulation (alignment, performance/speed and pitch regulation of the rotor blades).

They achieve coefficients of up to 0.52.
They are pretty close to the theoretical maximum..

Generators with a vertical axes (general):

The advantage of the generators with a vertical rotor axis is, that they function more independently from the wind direction and they are more tolerant to turbulent currents (as they often are in urban areas).

The layout of the generator and control system at the basis is a great advantage during the installation, commissioning and maintenance of vertical generators.

Generators with vertical axes (Darrieus):

The Darrieus rotor is, live the aforementioned generators with a horizontal axis, so called uplift generators with high rotation speeds of 5 – 8 and also require a high maintenance effort. They proved to be critical in their practical application. (Vibrations, overload protection and an imbalance susceptibility – partial icing, etc.). A 2 blade, and thus high-speed Darrieus rotor does not start by itself, it must be “started” electrically or with the assistance of a secondary turbine. The Darrieus rotors are currently the most efficient generators with a vertical axis, as they achieve coefficients of up to 0.4. The Darrieus wind generators have not yet been successful on the market, due to the aforementioned technical problems (starting, vibrations).