Introduction to wind turbine generators

Wind turbine Generators work on a simple principle: instead of using electricity to make wind—like a fan—wind turbines use wind to make electricity [1]. In a wind turbine generator, propeller-like blades spin around a rotor, spinning a generator, which creates electricity. As the wind blows across the rotor blades, a pressure gradient is formed between the upwind and downwind sides of the blade causing a resulting lifting force which pushes the blades clockwise around the main shaft.

Categorizing wind turbines

Generally, wind turbines can be divided into two types of horizontal- and vertical-axis turbines [1].

• Horizontal-axis turbines
• Vertical-axis turbines

Horizontal and vertical are defined based on the rotating axis of the wind turbine. Wind turbines with horizontal axes are what most people picture when thinking of wind energy. Most commonly, they have three blades and operate “upwind,” with the turbine pivoting at the top of the tower so the blades face into the wind. Moreover, wind turbines generators  can be categorized by installation location and how they are connected to the grid as the following

• Onshore or land-base Wind
• Offshore Wind 
• Distributed Wind

The wind turbine generators of today are much more complicated than the prairie windmills of the past. A modern wind turbine generator has as many as 8,000 different components [2]. Wind turbines are soaring to record sizes. The average rotor diameter of turbines installed in 2018 grew to 115.5 meters, up 141% since 1998–1999. There is also an increase in the average nameplate capacity of turbines, meaning they have stronger generators. In 2020, utility-scale wind turbines with 2.75 megawatts (MW) capcity were installed, 8% up from the previous year [2]. In this article, we aim at introducing some specifications of modern wind turbines like the latter ones.

Wind turbines specifications

In this article, we will talk about four main specifications of wind turbine generators: rotor diameter (RD), tip height (TH), tip clearance (TC), and hub height (HH). Let’s start with the rotor diameter of a wind turbine.

Rotor Diameter 

Rotor Diameter: is defined as the cross-sectional dimension of the circle swept by the rotating blades of a wind turbine. A great deal of progress has been made in the size of the RD since the start of modern wind energy use in the mid-1980s, as evidenced by the changes in equipment size installed [3]. In the mid-80s, small turbines with a capacity of an average of around 30 kilowatts and rotor diameters of below 15 meters were turned into machines with nominal power of five megawatts or above and with a rotor diameter of approximately 100 meters. In 2019, the average size of rotor diameter of wind turbines was 129 meters [3].

Optimization is very important in the energy industry because it is all about reducing the capital cost to stay competitive. One particular area of optimum wind turbine design is the tower hub height to rotor diameter aspect ratio. Current design standards set a fixed rate of 1-1.3 for the height to diameter ratio as this is the estimated best ratio to receive the most power output for the least cost [4]. Then, it is time to define the hub height of a wind turbine generator.

Wind Turbine’s Hub Height

A wind turbine’s hub height : is the distance from the ground to the middle of the turbine’s rotor. In a scientific report [5], researchers analyzed multiple different types of towers and found that one of the main limiting factors on tower hub height were crane height limitations. Current crane technologies are only economical up to 120-150 m hub heights where above this height requires specialized lifting towers. The other main limiting factor was that the maximum allowable diameter for the tower sections was 4.5 meters in order to easily transport them across roadways and under bridges. Above this diameter, the tower sections had to be quartered and re-assembled on site.

Tip Height and Tip Clearance

Finally, tip height is the total height of a wind turbine from the base to the highest point of it and tip clearance is the height that is including the distance between the tip of a blade and a stationary part of a wind turbine.

It is worth mentioning that modern wind turbines also have other main components including the tower, foundation, blades, gearbox, generator, and transformer which are not the subject of this article.

Did You Know?

WindEdition offers a detailed map for offshore wind energy generators projects around the world 

Including the correct coordinance, project name, capacity, and… you can checkout our Offshore Wind Map here.

Author: Hesam-Edin Hayati Soloot & Shahab Moghadam

References

[1] Department of Energy, “How Do Wind Turbines Work?”.

[2] Department of Energy, “Top 10 Things You Didn’t Know About Wind Power”.

[3] Statista, “Rotor diameter size of onshore wind turbines worldwide from 1990 to 2019”.

[4] Researchgate, “Design of Wind Turbine Tower Height and Blade Length”, written by Ryan Wass.

[5] Engström, S. e. (2010) “Tall towers for large wind turbines”, Project Report, Elforsk.