Wind is an important renewable energy source, which is exploited by horizontal or vertical axes wind turbines, converting the wind energy into mechanical energy, able to drive electric generators. The main target of modern wind turbine design is the possibility to capture a great level of energy in a broad range of wind velocity. The rotor of the wind turbine is the main element, collecting the wind energy in the form of rotational mechanical energy. In the efficiency assessment the number of blades are very important for a given wind speed. The present paper proposes a novel wind turbine structure, able to change the number of blades according to the actual wind speed, a patent proposal of the authors. The wind turbine efficiency is proved by numerical simulation.