Wind Turbines

What is a Wind Turbine?

Wind turbines are electro-mechanical systems that convert the wind’s kinetic energy into electricity (wind power). They are generally categorized as either horizontal axis (propeller style) or vertical axis (egg beater style) turbines:

• The horizontal axis wind turbine (HAWT) is the more efficient of the two designs, but it requires tall towers that are typically hard to transport and install. They also require constant realignment based to the wind direction.
• The vertical axis wind turbine (VAWT), on the other hand, do not have to be constantly aligned to the wind, but they have lower overall efficiency.

Because of the increased efficiency, the horizontal axis wind turbines are more common. There is increasing interest in residential or home wind turbines.

How does a HAWT work?

The figure illustrates the inner workings of an upwind HAWT. The main rotor shaft (and alternator located at the top of a tower) is pointed into the wind and must change its orientation concurrent to any change in wind direction. The yaw bearing supports the turbine as it swivels on its tower (termed yawing), a necessary action for upwind turbines.

Downwind turbines do not require this “yaw drive” as the wind, in effect, turns the rotor away from the moving air. In most cases, the turbine uses a copper alloy slip ring to connect the output terminals of a moving alternator to the cable that carries the electric current down the tower. The anemometer monitors the wind speed which, working through a controller, either starts the system (at minimum wind speeds generally ranging between 8 and 16 mph) or shuts off the system (at wind speeds in excess of 50 mph).

• The rotor assembly (typically including three blades) converts the kinetic energy of the moving air into rotational shaft energy.
• The alternator, connected to the rotor via a main (spinning) shaft, converts the rotational shaft energy into electrical energy (the result of creating an alternating magnetic field which in turn, induces voltage).

Either a mechanical brake (shown in figure) or “electrical braking” is required to stop the alternator rotor.