Horizontal axis wind turbines are commonly used for generating electricity offshore. (Haliade-150, with a capacity of 6 MW and diameter of 150 m) during installation. Fig. shows a schematic of a horizontal axis wind turbine. In simple terms, the wind exerts forces on the blades (lift and drag) and turns the rotor. A low-speed shaft is connected to the rotor. The gearbox transmits the power (rotation and torque) of the low-speed shaft to a high-speed shaft that spins a generator. Functions of the individual components of a wind turbine are explained briefly as follows:
Anemometer: Used to measure the wind speed. The collected data are transmitted to the controller unit, for instance, to stop the wind turbine at very high speeds (e.g. during hurricanes).
Blades: Harvest the wind energy. Wind exerts forces (lift and drag) on the blades, causing the rotor to spin.
Brake: Stops the rotor in case of emergency.
Controller: Starts the wind turbine at cut-in speeds (generally around 3.5 m/s) and shuts off the turbine at very high wind speeds (over 25 m/s, cut-outspeed) to protect the device.
Gearbox: Transmits the power (torque times angular speed) from the low-speed shaft to the high-speed shaft. The rotational speed required for a turbine is very high (≈1000 rpm) compared with the rotational speed of the rotor (≈20 rpm).
Generator: Produces the AC electricity.
High-speed shaft: Transmits the power from the gearbox to the generator, and rotates/drives the generator.
Low-speed shaft: Transmits the power from the rotor to the gearbox.
Nacelle: Houses the generating components of a wind turbine including the gearbox, generator, controller, and brake.
Pitch system: Adjusts the angle of attack of wind by turning the blades. The rotational speed and the generated power can be controlled/optimized by the pitch system. The pitch system can stop the turbine from rotating at cut-in or cut-out speeds.
Rotor: Consists of blades and the hub.
Tower: Supports the wind turbine. Towers are mainly built using conical tubular steel.
Wind direction: Upwind wind turbines (shown in Fig.) face into the wind, whilst downwind turbines face away from the wind.
Yaw drive: Aligns the turbines towards the wind. This keeps the wind turbine facing the wind when the wind direction changes for upwind turbines.
