The way a wind turbine works is the opposite of a rotating motor. While in a motor, the energy is consumed, but in a wind turbine that energy is generated in the form of electricity from rotating blades. Including wind, in most other technologies (non-renewable and renewable), rotating generators are the main electricity generation component, such as diesel, coal, natural gas, Wave, Hydro, Geothermal, Solar thermal, and Waste to Energy.
However, only two technologies solar photovoltaic [1] and fuel cells are ones where there is no use of rotating generators. Certainly, a generator is an important component of wind energy and now let us get to the details of how a wind turbine works.
How Does a Wind Turbine Generator (WTG) Work?
A wind turbine generator works with the force of the wind. Moreover, the kinetic energy of the flowing wind transforms into electrical energy by rotating turbine blades and the coupled generator. The wind turbine blades are similar to the wings of an airplane or helicopter blades. Where the same principle of lift and drag [2] makes the wind turbine rotate to produce electricity. The main resource to operate a wind turbine is the wind itself. Which varies all the time as it flows depending on the time of day, month, season etc. Thus capturing most wind energy in any location is not a straightforward task. So, to make a wind turbine work, the next two points are essential.
Wind and its speed
Cut-in-speed is the wind speed at which the turbine starts rotating. Where the cut-in-speed for most wind turbines is 5 m/s. In the same way, the maximum wind speed beyond which the turbine stops is the cut-out speed. Whereas, the cut-out speed for most wind turbines is 25 m/s. Noting, the range of 5 m/s – 25 m/s is considered as ideal wind speed to generate electricity from a wind turbine. The speed of the wind is so crucial that a very detailed wind mapping or analysis is done for a location before installing a wind turbine or a number of them. Exactly due to this wind turbines are characterized to work with different types of wind types and this feature is called Wind Class[3] of a wind turbine. Wind classes basically show what kind of turbine fits the “normal wind conditions” of a specific area. In addition, there is a theoretical maximum efficiency level called Betz Limit[4].
Location and Height of Turbine
A wind turbine can be installed anywhere wind is available with good speed. Like small wind turbines can be placed on rooftops or in the garden to power all or some household electrical loads. Whereas large wind turbines require a larger area. Furthermore, the more the height and larger the swept area of the blades, the higher the generation capacity.
Have you ever thought “WHY can you mostly find large wind turbines away in landscapes/countryside or the sea and not near your home or city”? The answer is due to “turbulent winds”. This means the wind available in cities with spread infrastructure has turbulent winds which are not suitable for large wind turbines. However, small wind turbines or vertical axis wind turbines[5] do operate in turbulent winds.
With the evolution of technology, the height of wind turbines is also increasing. The range of height above the ground is 30 m to 150 m. This height is from the ground to the center of the turbine also called the hub.
Operation And Components Of A Wind Turbine
Now let us have a look at each component of a wind turbine and understand its role in generating electricity from it.
Blades
The role of the blades is to capture the energy from the wind and rotate the turbine. Where the design of the blades of wind turbines plays a crucial factor in the power output. The more the number of blades, the more the wind is captured but it also increases the weight of the turbine. After the continuous evolution of wind turbine design, a three-blade design is most common now being the most efficient and stable. These blades are light in weight but sturdy enough to face high gusts of wind and extreme conditions. Fiberglass or fiber-reinforced polymers [6] (FRPs) are used to make turbine blades. The blades connect to the center or the hub which rotates along.
Hub or Rotor
The hub is the center of the turbine which rotates with the blades. The direction of the hub is normal to the direction of the wind. As told before the height of the turbine is from the center of this hub to the ground. Also, the swept diameter of the turbine is from the same hub till the end of the blades.
Gear Box
Direct-drive wind turbines or small wind turbines do not have a gear mechanism. It is in large wind turbines where small RPMs (rotation per minute) are converted to high RPMs with the use of gears. The low-speed shaft from the hub connects to the gear mechanism and the high-speed shaft from the gearbox turns the generator.
Generator
The wind turbine generator which gets rotational kinetic energy from the gearbox turns the magnets around a copper coil to generate current. The current is then transmitted via the turbine tower to the ground junction and transmission.
Control System
Wind turbine generators have internal control systems, that based on the size of the turbine could be only local or a part of a bigger control system on a utility scale. Small wind turbines generally start working as the wind blows and their vane system directs them to operate accordingly. In big turbine vane and yaw system analyses, the direction of the wind and computers operate the yaw system to direct the turbine in the wind direction. Similarly, anemometers constantly measure the real-time wind speed. Which guides the turbine to start rotation or to stop in case of very high speeds. Brakes are also there along the rotating shaft, to halt the rotation or to keep it going. All of this is a control system of the wind turbine. Software like SCADA and others act as the core of these control systems.
Nacelle
The rotating shaft, gearbox, generator, and control system are all inside the nacelle. In other words, you can say the rear of the turbine with all the electricity-generating equipment is the nacelle.
Tower
Either on the ground or at sea, wind turbines are placed on towers. The towers are made of steel and are very sturdy. Large wind turbines have a passage inside these towers to reach and access the turbine and all other equipment.
At Last
From the speed of the wind to the control system operating the wind turbine, we have covered most of it in brief. The basic technology of using the force of the wind and generating electricity remains the same. It is just the evolution of the same technology with large-scale adoption that is making this technology valuable.
References:
[1] – Solar Edition , What are solar photovoltaic panels made of? How do they Work? https://solaredition.com/what-are-solar-photovoltaic-pv-panels-made-of-how-do-they-work/
[2] Aerodynamic Forces: Definitions of Lift and Drag, URL: http://xn--drmstrre-64ad.dk/wp-content/wind/miller/windpower%20web/en/tour/wtrb/aeroforc.htm
[3] Wind Edition, What is wind class in wind turbine ? https://www.windedition.com/what-is-wind-class-in-wind-turbine/
[4] Wind Edition, What is Betz Limit for Wind Turbine Efficiency, https://www.windedition.com/what-is-betz-limit-for-wind-turbine-efficiency/
[5] ELPROCUS, What is vertical axis wind turbine: Working and its applications https://www.elprocus.com/vertical-axis-wind-turbine/
[6] Wind Turbine Blades: How composites power green energy https://www.tencom.com/blog/wind-turbine-blades-how-composites-power-green-energy
[7] post feature image: https://www.britannica.com/technology/wind-turbine
