Yaw system

[1] Their rotatable nacelles were mounted on the main structure of the windmill using primitive wooden gliding bearings lubricated with animal fat.

The active yaw systems are equipped with some sort of torque producing device able to rotate the nacelle of the wind turbine against the stationary tower based on automatic signals from wind direction sensors or manual actuation (control system override).

The active yaw systems are considered to be the state of the art for all the modern medium and large sized wind turbines, with a few exceptions proving the rule (e.g. Vergnet).

Alternatively in case of downwind turbines the tail fin is not necessary since the rotor itself is able to yaw the nacelle into the wind.

It is however unable to cope with the high moments required to yaw the nacelle of a large wind turbine.

[2] The yaw bearing can be of the roller or gliding type and it serves as a rotatable connection between the tower and the nacelle of the wind turbine.

This operation however greatly reduces the reliability of the electric yaw drives, therefore the most common solution is the implementation of a hydraulically actuated disk brake.

This is achieved with a simple industrial air pressure compression system (6–10 bar or 600–1,000 kPa or 87–145 psi) which is a reliable and low cost solution.

The combination of the large surface area of the fin and the increased length of the beam create a considerable torque which is able to rotate the nacelle despite the stabilizing gyroscopic effects of the rotor.

The required surface area however for a tail fin to be able to yaw a large wind turbine is enormous thus rendering the use of such a device un-economical.