Most horizontal-axis wind turbines turn to face changing wind direction. The blades rotate around the hub, while a separate yaw system turns the nacelle on top of the tower.
Small turbines often align with a tail vane. Utility turbines use sensors, motors and controls to move only when the direction change is large or persistent enough.
How utility turbines follow the wind
A wind vane on the nacelle measures direction, while an anemometer measures speed. The controller compares the wind direction with the rotor’s orientation.
If the misalignment exceeds the control threshold for long enough, yaw motors drive gears that rotate the nacelle around a bearing at the top of the tower. Brakes hold it in position after the move.
The controller avoids chasing every gust because constant yawing would increase wear and consume energy. Turbines in the same wind farm may therefore point slightly differently during variable conditions.
Upwind and downwind designs
Most modern utility turbines are upwind machines, with the rotor in front of the tower relative to the wind. They normally use active yaw control to keep the rotor facing the wind.
A downwind rotor sits behind the tower and can be designed to align more passively. The tradeoff is that the blades pass through the tower’s disturbed airflow, which can increase cyclic loads and noise.
Small horizontal-axis turbines commonly use a tail vane for passive alignment. Larger small-wind machines may use active yaw or other controls.
Yaw is different from blade pitch
Yaw turns the nacelle and rotor assembly around the tower’s vertical axis. Pitch rotates each blade around its own long axis.
Pitch controls rotor speed and power capture. It can also feather the blades so they produce little torque during high winds, faults or maintenance. Pitch changes do not point the whole turbine in a new compass direction.
Do the blades reverse direction?
Commercial turbine rotors are designed to spin in one direction. A change in wind direction causes yaw movement, not reversal of the rotor.
Electrical power converters allow variable rotor speed while maintaining grid-compatible output. The control system may stop and restart the rotor, but it does not normally reverse it to follow the wind.
What about vertical-axis turbines?
Vertical-axis wind turbines accept wind from different horizontal directions without yawing the rotor. That can simplify orientation, but it does not remove the need for controls, braking or a suitable wind resource.
Omnidirectional operation is not the same as high energy production. Turbulence, swept area, rotor efficiency and tested power performance still determine output.
Cable twist and yaw limits
Power and control cables run from the nacelle down the tower. Repeated rotation in one direction twists them, so the control system tracks yaw position and periodically unwinds by turning back when operating conditions allow.
Bottom line: horizontal-axis turbines change direction through active or passive yaw. Blade pitch controls the angle of the blades, while vertical-axis turbines generally do not need a yaw system.
Sources: U.S. Department of Energy wind-turbine component guide, DOE wind-turbine operation overview and DOE Small Wind Guidebook.