When thinking of a wind turbine we often think of tall towers and vast fields
Before the design of the Vertical Axis Wind Turbine, the image was accurate. On most conventional wind farms turbines were horizontal axis wind turbines (HAWT), which made them appear like a classic windmill. The concept of such wind turbines is that the large blades on a HAWT face the wind and transform its kinetic energy to shaft movement. This shaft transfers the rotation to a generator that produces electricity. The interesting thing about vertical-axis wind turbines is that there are other ways to harness this rotation. The option of using a vertical-axis wind turbine addresses many of the disadvantages of traditional wind turbines.
Although using HAWT for many years now, they have some engineering flaws like the efficiency theoretical limit called “Bentz limit” or the need to be directed toward the wind. Another disadvantage of them is the high speed needed to start the rotation, also called cut-in speed which you can read about here. VAWT is a design that can solve those two problems and do that with a smaller physical size.
What is a Vertical Axis Wind Turbine?
The Vertical Axis Wind Turbine (VAWT) is a turbine that has its main rotor shaft positioned transversely to the wind to generate wind power.
It then has the vertical axis wind at the bottom of the tower, where the vertical blades get support. Unlike the more popular Horizontal Axis Wind Turbine (HAWT) which has the blades attached to the horizontal rotor shaft. A VAWT design eliminates the need for pointing systems seen in the HAWTs because the turbine blades are omnidirectional. Omnidirectional means one direction, the shaft moves only if the wind is facing it. Contrary when the shaft is vertical It allows them to capture wind from any direction without having to be reoriented. The VAWT design also enables closer placement. So that more turbines can be situated in the same area or have higher energetic density.
Advantages of VAWT
There are several reasons why VAWT has great potential. It’s well likely that as this technology develops we will see more uses for it like the “Vertical sky A32” the world’s biggest operating VAWT. As for utility-scale, as reported in the American society of mechanical engineers Ørsted, the largest developer of offshore wind farms are already started working in this direction.
- Energetic Efficiency – Traditional horizontal wind turbines can theoretically convert about 60% of the wind flow to energy. For the vertical wind turbine, there is no such limit meaning more Watts for the same surface area. Which is a more efficient reference to the alternative. They also require less maintenance and
- Financial advantage – Since most wind farms are outside populated areas the fact the turbines can be closer to one another is great news. it opens the way to generate more power with less change to the environment. The vertical turbines can be more stable as a structure and reduce the installation cost land is a pricey resource so less use of it is economically efficient. Additionally, they consist of fewer moving parts which means lower upkeep costs.
- Practical – Horizontal wind turbines have their gear at the top of the tower carrying the turbine. Those towers reach immense heights, which makes the maintenance and technical fixes a lot more complicated. On a vertical turbine, the gear can be at the ground level, more accessible to both maintenance and upgrades.
- efficient use of lands – VAWT combines well with HAWTs as well as other alternative energy technologies like solar and water because they can produce energy in wind conditions that HAWTs cannot.
- Safer to life – unlike conventional HAWTs, which are placed higher in the typical migratory path of birds. VAWTs are large enough for flying wildlife to detect and avoid them from a distance. This is because of their slower rotation, constant blade speed, and lower profile. HAWT blades can sometimes spin so quickly that they occasionally seem to disappear in the air, which is a harmful surprise for birds. Additionally, VAWTs are more convenient for people to be around since they produce less noise pollution. Some researchers claim that noise pollution can have a few negative health effects from sleep to hearing loss. We covered those two topics in the article about wind power and everything you need to know for further reading.
Vertical Vs. Horizontal Axis Wind Turbine
Let’s start by explaining how a horizontal axis wind turbine (HAWT) operates. It utilizes the concept of “Asymmetric airfoil”. The effect is similar to the design of airplane wings, the difference in air pressure around the blade is governing the movement. Being omnidirectional, we always need to adjust the direction of horizontal turbines to ensure it’s perpendicular to the wind. For that function, we use a device to rotate the turbine into the wind and to change the blade pitch.
Once we finish positioning the turbine in the right direction the blades hit the wind and rotate a shaft. In turn, the shaft will transform the rotational motion into a gearbox. The last is adjusting the rotation speed of the shaft to the operational one of the generator. All of those kinetic transformations result in major energy loss. The practical meaning of all those mechanisms is the need for more frequent and longer maintenance.
The profile of the Vertical Axis Wind Turbine (VAWT) is distinctive in shape and there are a lot of different designs. It consists of a few identical “blades” with a vertical orientation displaced symmetrically around the shaft. This arrangement saves the artificial positioning to enhance electricity production because they are equally facing the wind in any direction. on top of that, the blades are less exposed to fatigue of materials due to the symmetrical loading. This fact gives vertical wind turbines the possibility to have a longer lifespan. The VAWT’s lower mechanical complexity compared to the HAWT reduces the frequency and difficulty of maintenance and saves on costs. As mentioned before almost all maintenance work can be done from the ground.
Offshore Farms With VAWT Are More Energy Dense
Vertical axis wind turbines (VAWT) have the potential to dramatically increase the power density on offshore wind farms. Dr. Pablo Ouro, a researcher from the University of Manchester examined various spacing arrangements at offshore wind farms with 25 10 MW turbines arranged in five rows. Afterward, he published a white paper covering his simulations. He demonstrated how VAWT outperformed horizontal-axis wind turbines in all of the cases studied.
The reason is the lower radius of interference between adjacent elements in the array. The report suggests a drawback in traditional horizontal turbines is that they leave a long trail of turbulence behind them that prevents another turbine to work. Vertical turbines cause less of a turbulent train resulting in more effective arrays. Additionally, a slender VAWT element will outperform a wider one on this parameter. There are thin-diameter turbine designs that compensate for the loss in the area by extending the height. You can see an example in the promotion video wind spire energy made.
Norway’s Plan For A 1MW Floating VAWT Installation
The Swedish company SeaTwirl, specializes in the development of offshore wind farms. They signed a contract with Westcon to construct and install a 1-MW commercial-scale array in Norway. SeaTwirl claims that its floating vertical-axis wind turbines have the potential to significantly reduce the cost of deep offshore wind energy. Taking into consideration the fact that infrastructure development offshore is an extra expensive and complicated mission. You probably start to see where is the excitement about vertical turbines coming from.
This wind farm is planned 700 meters off the coast in Boknafjorden, northeast of Lauplandsholmen. The northern sea can reach a depth of 130 meters in this area. Each planned element will have a 50 m diameter and a height of 55 m mounted on 80 meters submerged platform. To increase the efficiency even further they plan to connect the project to an already-existing onshore transformer substation.
SeaTwirl and Haugaland Kraft signed an agreement to trade the generated electricity. The first publication of the agreement was in 2018. The company said that they are concentrating on enhancing the turbine’s design and reducing potential dangers until the project will get the permits. The technology SeaTwirl uses is a set of floating vertical-axis wind turbines placed un in underwater towers. They consider modifying the location of the generator and bearing housing just above the water’s surface. This will lower installation and maintenance costs and shorten downtime.
Wind turbines with no blades
A company named Vortex has designed a unique type of wind turbine, one that converts vibration into electricity. Although their design is behind in the power capacity, they make wind energy accessible to new audiences. They explain they see their product as part of an urban area, and with fewer moving parts they solve problems of traditional designs. The first is a noise problem that in many cases prevents permits for wind energy generating in urban areas. The second is the safety of birds and flying animals. We see it as a great added value for a company that tries to solve sustainability problems. You can see the full video of them explaining the product here.
To conclude
The accelerating adoption of vertical design emphasizes the understanding that to reach net zero carbon we need more than one solution. There are many different needs around the globe as well as different availability of wind as you can see on the wind atlas or of sunlight. Therefore we need a more flexible suite of solutions so that every community can easily take a part in the change. We will keep updating you as manufacturers announce new designs and in the meanwhile share your taught with us in the comments.
