How does a wind wheel function (operate, work)?

How does a wind wheel start and how does it work? How much electrical energy can a wind power system (plant) gain (obtain) from the wind at a maximum (at best)?

Wind power plants are meant (intended) to generate (produce) electrical energy. Thus, the built-in generator plays (takes) a special part (role). If the wind hits the wing of such a turbine, it makes the rotor revolve (rotate, turn). The faster the shaft rotates the larger the produced amount of electricity. This electricity can be used to (easily) supply houses with favo(u)rable wind conditions (at a windexposed locality/spot/place) without problems. It is possible for large wind power systems (Large wind power systems are able) to feed electricity into the public power lines and thus supplement the energy from coal, oil, and nuclear power stations (plants).

The numerous kinds of wind wheels(?) can be divided into two main groups: The horizontal axle (axis) wheels, that e.g. for wind mills have been built for several centuries as well as those wheels whose propellers turns around a vertical axle. Most of today's wind power systems have propellers with three blades (wings) driving a horizontal shaft.

To control the speed, the providers of the wind power systems usually (notably) use (make use of) the possibility of turning the wings a little so that (thus giving ...) the attacking angle (angle of impact) is slightly varied (different). That way the speed can be reduced in cases of extremely (excessively) strong wind (Thus, in conditions of extremely strong wind, the speed can be reduced). Apart from (Besides, Other than) this wing brake the plant is provided (equipped) with a mechanical brake mounted (installed, attached) to the rotor shaft. At critical wind speeds of 25 m/s -- that equals (is equivalent to, corresponds to) 90 km/h -- the brake is applied (actuated).

Since the wheel only starts at medium wind intensities, larger wind turbines mostly (most of [the?] time) have to be started by a small motor. During this time (time span) the wind power system is a consumer and not a generator of current. In favo(u)rable wind conditions a wind wheel is theoretically able to convert 59 percent of wind energy into electrical current -- realistic figures of modern wind turbines nowadays range at 40 percent at the best (at most).