| Homebuilt Wind Turbine Explained |
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Vertical Axis Wind Turbine
Wind power generators comes in different designs, some have proven to be more successful than others. Every model has its advantages and disadvantages and the most commonly used today is the Horizontal-axis(HAWT) design.
Construction Drawbacks
Its cousin, the vertical axis design(VAWT), is not as widespread used. The type of drawbacks this construction brings is likely to be the reason over why it is the less commonly used. A VAWT operates very close to the ground in comparison to a HAWT, by a rule of thumb wind velocity increases with altitude, that means less energy can be extracted from a power generator that works closer to the ground thus not making it as efficient. The difficulties in mounting this type of turbine to towers makes it a less viable alternative for most of the companies willing to invest in wind power.
In the picture above, a box located directly under the turbine can be seen, this is where the gearbox and the generator is located. This is actually a good thing as the tower does not need to carry the weight of the equipment. This design is also easier to maintain because the generator is located on the ground which also makes it a more safe environment to work in. Although the VAWT has some advantages over the HAWT, the design is not as well suited for large scale wind power projects. It's just not as versatile, when it comes to fitting in different environments the horizontal-axis design is superior. Its need for flat areas of land to build on, height limitation in construction, need for strong steady wind flow, economics and environmental impact upon migratory birds makes it a less feasible choice.
A wide variety of of VAWT configurations have been proposed, beginning with the old Persians constructions used to pump water and grind grain over a thousand years ago, to the Darrieus design invented in 1926 by George Darrieus. One of the largest wind power generator ever designed was the Eole Darrieus built near Quebec in Canada, with a rated output of 3.8MW, the system was 96 meters high and 64 meters in diameter and a rotor weighing 100 tonnes. Darrieus' 1927 patent also covered machines with straight vertical axis blades called Giromills
Savonius VAWT
Other configurations include the Savonius VAWT, which is popular because of the simplicity of manufacture, and the straight bladed VAWTs. The latter include the Musgrove turbine that was developed culminating in successful testing of a 500kW device at Carmarthen Bay in the UK (Peace, 2004).
There is not so much information on vertical axis wind turbines available, the reason being how it failed in the commercial wind power market. A Giromill derivative named cycloturbine was produced and marketed for some time but could never really compete with other more successful types in the market. All in all the vertical axis design belong more to the past.