The growth in interest in renewable energy has given rise to a lot of new wind turbine designs. Some of the recent models include the vertical-axis wind turbines that are efficient, economical, and better suited for residential energy production. They are quiet and especially suited for urban environments.
How does a Vertical-axis Wind Turbine Work?
You will come across two different designs of vertical-axis wind turbines. The first one is a Savonius rotor and the other is a Darrieus model.
A Savonius rotor is what you get when you cut a 55-gallon drum in half and offset the two halves and place it on a shaft that rotates. It is inefficient, low-tech and very similar to an anemometer. This design operates in a 5 to 10% efficiency range.
A Darrieus rotor resembles an egg beater. It uses an airfoil design like an airplane wing that is built with a flat side and a curved side. These airfoils are secured to a hub which is further attached to a generator shaft. When the air passes through, it is converted into rotational momentum which helps to spin the generator.
A vertical axis turbine operates with lesser efficiency compared to a horizontal axis turbine. Some other factors include increased maintenance, weighing more, and lower energy production.
How to Design Small Vertical-Axis Wind Turbines
Once you are settled on an airfoil, you must calculate a concave orientation, width, angle, and quantity because these factors determine the overall performance of the VAWT.
Firstly, you should choose a low-speed airfoil and then place the concave orientation outside. After that, you choose a small blade angle with a suitable blade width. It is recommended to use a socket structure because it is easy to install and reduces drag forces. All of these factors together help to determine the power generation performance of your VAWT.
They have adopted the design of small VAWTs even while in the manufacturing process of medium and large VAWT technologies. A VAWT is noiseless, safe and doesn’t require a tall tower. But due to the problems of self-starting, safe braking, aerodynamic efficiency, and structural stability, commercialized large VAWT have not been launched.
VAWTs must use the “positive pitch attack angle regulation”. This feature uses centrifugal forces to control the blade angle when the speed for rotation exceeds the rated speed.
Truss Structure for the Main Shaft in a Large VAWT
A larger rotor diameter will give you an extremely large bending meter. Furthermore, a shaft with a large and strong diameter makes commercialization difficult.
As a solution to this, you can use a hollow truss inside, as the main shaft. A truss has a relatively light yet strong structure. It meets all the essential requirements for the main shaft on medium as well as large VAWTs and the demand for commercialization.
Three Major Problems with VAWT
- Low-power generation performance
- Reduced power output
- Poor stability shortens the lifespan of the turbine
A vertical axis design known as SWAT helps in solving all these three technical problems of the vertical axis wind turbine industry.
Advantages of VAWT over HAWT
There are many drawbacks of both these technologies, but VAWT has three basic advantages.
1. Fewer Components
The main rotor shaft is oriented vertically which offers a reduction in parts. The blades in a VAWT can catch wind from any direction without direction orientation. You do not require any components to control yaw and pitch.
It is a safer alternative as you do not have to climb up tall towers. The maintenance costs are reduced because generators and electrical/ mechanical components are at ground level. So you can avoid climbing gear, lifts, and danger-pay compensation.
3. Scaling Down
This design is efficient to use in dense urban areas or rooftops where any other renewable technologies do not work.
Some reasons why people are skeptical of adopting this technology on a wind farm are:
Just a fraction of the blades on VAWTs generate torque and the rest of the parts just go along. This results in reduced efficiency in power generation. The main reason why developers prefer HAWT is that no prototype of VAWT had the generating capacity close to horizontal-axis designs. They are not good for long-term investment.
2. Scaling Up
There are many obstacles to scaling VAWTs to commercial size. They do not have sturdy construction. It needs to be secured with many long guy-wires.
3. More Maintenance
A VAWT design has fewer components that require regular repairing. The forces acting on this machine are far more turbulent.
Smaller VAWTs generate lateral stress that can be accounted for with sturdier materials and regular maintenance.
Finally, vertical axis wind turbines take up more materials and labor but are less efficient. The noise pollution factor highly depends on the machines rather than the technology it is made out of.
Table of Contents
- How does a Vertical-axis Wind Turbine Work?
- How to Design Small Vertical-Axis Wind Turbines
- Truss Structure for the Main Shaft in a Large VAWT
- Three Major Problems with VAWT
- Advantages of VAWT over HAWT