When you imagine wind turbine you probably think of turbine we all know on open field. You might have also made a school project using a dc motor. In today’s world interest in renewable energy options has given rise to a rash of new wind turbine designs.
Some of the most recent models on the market are vertical axis wind turbines (VAWTs), which manufacturers claim are quiet, efficient, economical and perfect for residential energy production, especially in urban environments.
Different types of Vertical Axis Wind Turbine
#1. Different types of Turbines
Wind turbines can rotate about either a horizontal or a vertical axis.
Horizontal Axis wind turbine : Large three-bladed horizontal-axis wind turbines (HAWT), with the blades upwind of the tower produce the overwhelming majority of wind power in the world today. These turbines have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind.
Vertical-axis wind turbines (or VAWTs) have the main rotor shaft arranged vertically. The turbine does not need to be pointed into the wind to be effective, which is an advantage on a site where the wind direction is highly variable. The generator and gearbox can be placed near the ground, using a direct drive from the rotor assembly to the ground-based gearbox, improving accessibility for maintenance. However, these designs produce much less energy averaged over time, which is a major drawback.
Difference between HAWT and VAWT
VAWT are the modern turbine, they are sub divided in to types are as follows
1. Darrieus wind turbine
Darrieus turbines, were named after the French inventor, Georges Darrieus. They have good efficiency, but produce large torque ripple and cyclical stress on the tower, which contributes to poor reliability. They also generally require some external power source, or an additional Savonius rotor to start turning, because the starting torque is very low.
A subtype of Darrieus turbine with straight, as opposed to curved, blades. The cycloturbine variety has variable pitch to reduce the torque pulsation and is self-starting. The advantages of variable pitch are: high starting torque; a wide, relatively flat torque curve; a higher coefficient of performance; more efficient operation in turbulent winds; and a lower blade speed ratio which lowers blade bending stresses. Straight, V, or curved blades may be used.
3. Savonius wind turbine
These are drag-type devices with two (or more) scoops that are used in anemometers, Flettner vents (commonly seen on bus and van roofs), and in some high-reliability low-efficiency power turbines. They are always self-starting if there are at least three scoops.
GIF containing two VAWT and one HAWT demonstration
#. TechFact: Why are turbine white in color.
Answer: White is neutral and non-intrusive. White color almost completely blend with cloudy background when seen below it. According to International aviation law large structures to be white to make visible for the pilots. Also white reflect sun which heats up composite and steel.
Wind Turbine painted white in color
#2. Advantages & Disadvantages of VAWT
- Generator is present in the base, therefore it is maintain easily.
- Do not need to be oriented towards winds, as they are omnidirectional. Also they do not require yaw pitch to control.
- VAWT can work in turbulent and gusty winds.
- Can be use in rooftops, urban area, traffic area etc.
- Many VAWT can be group close together.
- Complex geometry, suffer from wide variation of angle attack and installation problem.
- Less reliable, less efficient as wind hitting blade on the front are producing torque.
- Self-starting problem on low wind speed.
#3. How Energy Efficient a VAWT is?
Accordingly, Betz’s law gives the maximal achievable extraction of wind power by a wind turbine as 16/27 (59.3%) of the total kinetic energy of the air flowing through the turbine.
The maximum theoretical power output of a wind machine is thus 16/27 times the kinetic energy of the air passing through the effective disk area of the machine. If the effective area of the disk is A, and the wind velocity v, the maximum theoretical power
Betz’s limit theoretical maximum efficiency, power equation and efficiency between VAWT and HAWT
Example: Air density = 1.23 kg per cubic meter at sea level. Swept area = pi x r squared. Our 2 foot blades = 0.609m, 4 ft = 1.219m. 10 mph = 4.4704 m/s, 20 mph = 8.9408 m/s.
How much power is in the wind: 2 ft blade, 10 mph winds = .5 x 1.23 x 3.14×0.609squared x4.4704 cubed = .5 x 1.23 x 1.159 x 89.338 = 63.7 watts
That’s the MAXIMUM power in the wind. However, it’s impossible to harvest ALL the power. The Betz Limit tells us that the maximum percentage of power we can harvest from the wind is 59.26%.
Thus our maximum power would be: 2 ft blades, 10 mph wind = 37.7 watts
#4. Three Application Windspire, Arborwind & Enlil
1. The Windspire, a small VAWT intended for individual (home or office) use was developed in the early 2000s by US company Mariah Power. The company reported that several units had been installed across the US by June 2008.
2. Enlil is a smart vertical axis wind turbine project that transforms highways into renewable energy sources by using the dynamics of the city. Enlil has soler panel at its top, hence it generate energy from natural wind as well as from sun. It will also measure the city’s temperature, humidity, wind and CO2 by using the the build-in sensors and the IoT platform.
3. Arborwind, an Ann-Arbor (Michigan, US) based company, produces a patented small VAWT which has been installed at several US locations as of 2013.
Windspire, Enlil and Arborwind respectively
#5.Is VAWT worth based on efficiency?
There are applications where a vertical axis wind turbine can be used. There are small applications where efficiency is not the main concern. In this instance, certain Savonius designs would work wonderful for this application.
There are many innovator who build their own DIY VAWT from scratch to light up a fan or tubelight. Many metro cities uses VAWT in traffic area to generate power from moving traffic.
#6. DIY Wind power paper turbine
Since we are learning about turbines, I thought why not make a small own paper fun project as we done in our previous blog. Three paper strip are cross connected, when air strike on paper each blade produce torque and provide rotational momemtum.
#. Reference & Conclusion
Finally here we conclude the article on VAWT, Hope you liked it. Do follow BlogTheorem on Social Media and check out other awesome, knowledgable content amplified to maximum.