Yaw system
The motors, gears, bearing and brakes that rotate a wind turbine nacelle about the tower axis to keep the rotor facing the wind.
Horizontal-axis turbines must point the rotor into the wind to capture energy. The yaw system consists of a large slewing ring between tower top and nacelle, several electric (occasionally hydraulic) yaw drives with planetary gearboxes engaging a toothed ring, and friction or hydraulic brakes that hold position between movements. Large offshore turbines may carry 10–20 yaw drives.
The controller reads wind direction from a nacelle vane or ultrasonic anemometer, increasingly supplemented by nacelle-mounted lidar, and yaws when the averaged misalignment exceeds a threshold, typically 5–10°. Yaw rates are slow, about 0.3–0.5° per second, to limit gyroscopic loads on the rotor.
Power loss from misalignment follows approximately:
A persistent 8° error, often caused by a miscalibrated vane, costs about 1–3% of energy. Correcting static yaw offsets with lidar or SCADA analytics is one of the cheapest yield improvements available to operators.
Yaw also has other roles: unwinding twisted power cables after several full rotations, parking the rotor safely in storms, and deliberate offset for wake steering. Downwind and some floating designs use passive yaw, letting aerodynamic forces align the rotor. Yaw bearings and gear wear remain a known maintenance item, particularly in turbulent sites.
Related terms
All terms →- Pitch control
Rotation of wind turbine blades about their long axis to change the angle of attack, used to regulate power above rated wind speed, start up, and stop the rotor.
- Wake effect
The reduced wind speed and increased turbulence downstream of a wind turbine, which lowers the output and raises the fatigue loads of turbines located behind it.
- Cut-out wind speed
The wind speed at which a turbine shuts down or ramps down to protect itself from excessive loads, typically 25 m/s (10-minute mean) for utility-scale machines.
- Power curve
The relationship between hub-height wind speed and a turbine's electrical output, used with a wind speed distribution to estimate annual energy production.
- Floating offshore wind
Wind turbines mounted on buoyant platforms moored to the seabed, enabling wind farms in water deeper than about 60 m where fixed foundations become uneconomic.