Basic Overview Of How A Wind Turbine Works
A wind turbine system; also known as a wind energy conversion system (WECS); is essentially used to intercept the wind and extract the energy, by converting the kinetic energy in the wind into mechanical energy.
The turbine blades intercept the wind, thus creating friction, which causes the blades to ‘lift’ and rotate. This in turn spins a shaft, which goes into a gearbox and increases the rotational speed, before finally driving the generator to produce electricity.
The most common type of turbines that are used to generate electricity for the national grid are of a horizontal axis configuration. This design comprises of rotor blades; 1, 2 or 3, but most commonly 3; which rotate around a horizontal hub that is connected to a gearbox and then a generator. These components, along with all the electrical components are housed in a nacelle, which is located and mounted at the top of the tower.
In addition, there are sometimes sensors and a yaw mechanism, which detect the wind direction and turn the tower head to face the wind. This is often known as an upwind configuration and the wind blows over the turbine blades, with the nacelle and tower located behind. However, sometimes the turbine is fixed facing one direction and this is typically a downwind configuration. In this situation, the wind blows over the tower, prior to the blades.
Power Production
The height of the tower and the size of the rotor blades dictate how much power can be produced from the turbines. Therefore, the larger the swept area, the more wind intercepted, and the greater the tower height, the stronger wind speeds can be intercepted.
Wind turbines are configured to operate above cut-in wind speeds and below cut-out wind speeds for the following reasons:
· Below the cut-in wind speed, it would be difficult to operate the wind turbine smoothly because the amount of power generated would be so small, and therefore it does not operate.
· Above the cut-out wind speed, the turbine is shut down and does not produce any power to avoid any structural damage.
Therefore, power is produced from the wind turbines between cut-in wind speed and cut-out speed, but above a certain value known as rated power, the power generated is limited to this value.
Power Control
There are two types of system mechanisms that can be implemented to control the power output from the rotor blades: stall and pitch control.
Stall control; also known as passive control; can control the power output using the aerodynamic properties of the blades. The twist and thickness of the rotor blades vary along the length of the blade and when the wind speed becomes to high, turbulence occurs behind the blade. This turbulence results in less energy from the air being transferred, thus minimising the power output at higher speeds.
Pitch control involves adjusting the angle of the rotor blades and this type of control mechanism has built in braking: where by when the blades become fully ‘feathered’, they essentially come to a standstill.
Turbine Design
There are two main types of wind turbine designs:
· horizontal axis turbines and
· vertical axis turbines.
Horizontal axis turbines are most commonly used and are either 1, 2 or 3 bladed designs; however, today the market is mainly dominated by 3 bladed designs. They can either be configured as upwind or downwind rotors relative to the tower, however, the majority tend to be upwind as they are better at handling larger rotor diameters.
Vertical axis turbines can be split into two sub categories, which depend on how they operate. These either operate using aerodynamic drag forces or have aerofoil blades that are capable of generating lift.
The main difference between horizontal axis and vertical axis designs are the part(s) of the construction that rotate. The horizontal axis design uses angled propeller type blades to create friction when facing the wind, which results in blade rotation, where as the vertical design uses the wind to spin on a centre point on the ground, which results in the whole construction rotating [1].
References:
[1] How do wind turbines work:
http://www.clean-energy-ideas.com/articles/how_do_wind_turbines_work.html
Bibliography:
· Twidell, J & Weir, T., (2006), Renewable Energy Resources. 2nd Ed. Oxon: Taylor & Francis
