60 seconds: Vertical axis wind turbines
What are vertical axes wind turbines (VAWTs) and how do they rotate? Our new 60 seconds video lecture explains this and shows the advantages of VAWTs. However, the Horizontal Axis Wind Turbine (HAWT) is the dominant wind turbine on the market, althought Vertical Axis Wind Turbines have been in the running for a long time too. The VAWT has been pursued in different projects, but so far never reached commercial ‘breakthrough’.
VAWTs are less popular then HAWTs, probably due to the initial perception that VAWTs cannot be used for large scale electricity generation. They are known to be less reliable and less efficient than HAWTs and have some drawbacks. Firstly, the rotor is built lower to the ground. As the wind speed grows with height, they experience lower wind speeds. Also, VAWTs are less efficient, which can be related to the additional drag that is caused by the blade rotating into the wind. This results in a lower rotation speed and thus in a lower power output. Furthermore, they experience higher cyclic fatigue as the blades move both up and downwind. This can lead to severe fatigue on both the blade and the drivetrain. Lastly, VAWTs are usually not self-starting and thus require a starting mechanism.
In more recent years, offshore project developers have become interested in VAWT projects, especially for floating offshore wind farms. VAWT’s offer advantages relative to HAWT’s when it comes to floating substructures. The rotor and generator of a VAWT are located at the base of the structure and therefore the centre of gravity is lower, which will improve floating stability and requires a smaller floating support structure. Also, as the drivetrain is closer to the surface, maintenance operations will be easier, safer and less time consuming. Finally, the wind turbines are omnidirectional, or independent of inflow direction. This means that unlike a HAWT, no yawing mechanism is needed for a VAWT. As a result, floating VAWT wind turbines would require less material, will have less downtime and less components then a HAWT and that could reduce costs for offshore wind energy.
Although this sounds very promising for VAWT turbines, there are still some challenges that need to be addressed. Especially the fatigue caused by cyclic loading remains a problem that needs to be researched further. All in all, Vertical Axis Wind Turbines have not had great success yet in the onshore wind energy industry but may have future potential as offshore floating structures.
More 60 seconds
You can still watch the previous 60 seconds lectures on offshore energy here. Is there a topic you would like to learn more about? Please let us know at email@example.com and we will consider adding it to our series.