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Introduction to Unconventional Windmills – Helix Wind Turbines for Small Wind.
Helix wind turbines are vertical axis wind turbines and there are two distinct types- the Savonius and the Darrieus- both named after their inventers.
They are both installed relatively close to the ground, compared to a horizontal axial wind turbine; therefore they depend on optimum wind speeds at around 15’.
This is an article on residential, small wind turbines and here we have a look at the helix design. We begin with an overview of the two types of helix turbines, going on to examine the design and operation of these unconventional helix wind turbines for small wind.
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Overview of Savonius and Darrieus Helix Vertical Axis Wind Turbine (VAWT).
- Savonius Wind Turbine
This is a wind-drag turbine which means that the wind “drags" the three S shaped blades. It is built up in a modular form, the blades being constructed by stacking the sections above each other. It is very slow revving (under 100 RPM) so is more suitable to agricultural and pumping purposes than producing electricity. Nonetheless, there are numerous models available that are producing electricity noiselessly, if not that efficiently.
- Darrieus Wind Turbine
This is a wind-lift turbine in that the wind gets under the three helix-formed blades causing the turbine to “lift." Its design roughly resembles that of an upside down egg-beater, which can utilize air coming from all directions, negating the need for yaw controls. This along with low cut-in speed makes the Darrieus design ideal for low-level turbulent air flows, with the new technology encouraging more people to buy a helix wind turbine.
Note: Images from http://www.helixwind.com/
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Operation of Darrieus Helix Wind Turbines for Small Wind.
Because the Darrieus design is more suited to small wind turbines, we will examine how they operate using the Quietrevolution qr5 small wind helix turbine as an example. (See Image below.)
The vertical axis wind turbine has a number of blades in the shape of a helix. A helix blade is really a straight blade tapered at each end, but with a twist in the middle.
The blades are vertical and run from the top of the turbine to the bottom held in place by spider supports, the flat section in the middle of the blades catching the wind and causing them to rotate. Because of the helix shape, the blades can scoop up the wind from any direction; this is a big bonus as yaw or pitch mechanism is not required also saving weight, energy, and reducing noise levels.
There are thrust bearings fitted at the top and bottom of the blade central shaft, since the wind attempts to “lift" the turbine. This is prevented by the thrust bearings, and consequently the kinetic energy of the wind is converted to mechanical energy.
Attached to the bottom of the blades is a generator, which being direct-driven negates the use of a gearbox, reducing noise and weight. It also has the advantage of being accessible for maintenance.
As well as ground-mounted, the turbine can be mounted on a mast of 35’ or rooftop mounted, using a 6' mast bolted to the gable end of the house.
Darrieus helix turbines can also be mounted on flat roofs using ground-mounting kits, and along with photovoltaic panels as a hybrid system.