The turbine (1) has a rotor (2) rotatable around a vertical axis under effect of air stream, and air guiding elements (5) surrounding the rotor in an external side. A rotor shaft is coupled with a generator, and the rotor surrounds a flow channel (4), which comprises a flow deflecting surface (7) for deflecting the airflow to an outlet opening (13). The deflecting surface exhibits a conical shape, and the flow channel exhibits a cross section that is reduced in an airflow direction. The air guiding elements are designed as profiled air guiding vanes.
