Unconvential Wind Turbines

Unconvential Wind Turbines

List of Uncoventional WInd Turbines

As of 2009, the most common type of wind turbine is the three-bladed horizontal-axis wind turbine (HAWT). This article deals with various types of wind turbine that differ from the standard type.

Ducted Rotor

Still something of a research project, the ducted rotor consists of a turbine inside a duct which flares outwards at the back. They are also referred as Diffuser-Augmented Wind Turbines (i.e. DAWT). The main advantage of the ducted rotor is that it can operate in a wide range of winds and generate a higher power per unit of rotor area. Another advantage is that the generator operates at a high rotation rate, so it doesn't require a bulky gearbox, so the mechanical portion can be smaller and lighter. A disadvantage is that (apart from the gearbox) it is more complicated than the unducted rotor and the duct is usually quite heavy, which puts an added load on the tower. The Éolienne Bollée is an example of a DAWT.

Maglev wind turbine

A maglev wind turbine uses magnetic levitation to replace conventional bearings in the design of a wind turbine. Magnetic bearings have been used for smaller turbines and pumps, but they generally can't handle impacts disturbing the shaft and require actively controlled electromagnets. Making magnetic bearings strong enough to handle the loads of a wind turbine would use prohibitive amounts of power just keeping the electromagnets running. A recent design employing permanent magnets was developed in China by Guangzhou Energy Research Institute under the Chinese Academy of Sciences and with Chinese company Zhongke Hengyuan Energy Technology Co. Ltd. Little detailed technical information supporting these claims is yet available in English.^[1][2]

The design claims to utilize winds with starting speeds as low as 1.5 meters per second (m/s), and cut-in speeds of 3 m/s. This could add 1,000 hours of operation annually to wind power plants in areas with an average wind speed of 3 m/s. This contradicts the engineering practice in wind turbine siting; sufficient wind resource is required to make a project feasible. Since the energy available in wind varies as the third power of wind speed, the power produced at such velocities would be much lower than conventional wind turbines under higher speed winds and as such unlikely to produce enough energy in total to justify the capital expense of turbine installation.

Co-axial, multi-rotor horizontal-axis turbines

Two or more rotors may be mounted to the same driveshaft, with their combined co-rotation together turning the same generator — fresh wind is brought to each rotor by sufficient spacing between rotors combined with an offset angle alpha from the wind direction. Wake vorticity is recovered as the top of a wake hits the bottom of the next rotor. Power has been multiplied several times using co-axial, multiple rotors in testing conducted by inventor and researcher Douglas Selsam, for the California Energy Commission in 2004. The first commercially available co-axial multi-rotor turbine is the patented dual-rotor American Twin Superturbine from Selsam Innovations in California, with 2 propellers separated by 12 feet. It is the most powerful 7-foot diameter turbine available, due to this extra rotor.

Counter-rotating horizontal-axis turbines

Counter rotating turbines can be used to increase the rotation speed of the electrical generator. As of 2005, no large practical counter-rotating HAWTs are commercially sold. When the counter rotating turbines are on the same side of the tower, the blades in front are angled forwards slightly so as to avoid hitting the rear ones. If the turbine blades are on opposite sides of the tower, it is best that the blades at the back be smaller than the blades at the front and set to stall at a higher wind speed. This allows the generator to function at a wider wind speed range than a single-turbine generator for a given tower. To reduce sympathetic vibrations, the two turbines should turn at speeds with few common multiples, for example 7:3 speed ratio. Overall, this is a more complicated design than the single-turbine wind generator, but it taps more of the wind's energy at a wider range of wind speeds.

Appa designed and demonstrated a contra rotor wind turbine in FY 2000–2002 funded by California Energy Commission. This study showed 30 to 40% more power extraction than a comparable single rotor system. Further it was observed that the slower the rotor speed, the better the performance. Consequently Megawatt machines benefit most. This also cancels the gyroscopic forces. There will be an improvement in overall efficiency.

Furling tail and twisting blades turbines

In addition to variable pitch blades, furling tails and twisting blades are other improvements on wind turbines. Similar to the variable pitch blades, they may also greatly increase the efficiency of the turbine and be used in diy construction

Telescopic blades

The next step in making improvements to wind turbines is the use of telescopic blades. Telescopic blades can change the blades length thus increasing or decreasing the turbines swept area. Telescopic blades make a turbine more productive by increasing the turbines rotor diameter during low wind conditions. In high wind conditions when the turbine is in need of reducing loads the blades can be retracted to make the rotor smaller.

Aerogenerator

The Aerogenerator is a special design of vertical axis wind turbine which could allow greater energy outputs.

Savonius wind turbine

The Savonius wind turbine is another special design wind turbine.

Augmented "G" model VAWT: "G" Model Wind Turbine (GMWT)

The "G" Model VAWT Turbine is equipped with three -self directioning- "Augmentation And Directioning Wings=AADW" placed outer section of classical Darrieus blades. The GMWT is capable to increase almost fivefold the efficiency of classical Darrieus Blades: ^[5] AADW adjust itself to the wind direction without any external power. The result combination ("G" Model Wind Turbine) need very low cut-in wind speed, has self starting ability togetherwith high capacity factor. Detailed information is available in: http://www.windturbine-performance.com

Aerial

It has been suggested that wind turbines could be flown in high speed winds at high altitude taking advantage of the steadier winds at high altitudes. The Magenn Power Company will soon begin manufacturing their Magenn Flying Wind Turbine for commercial use.

A kite system that mines the kinetic energy of the wind resulting in mechanical energy tensioning the tether has an rotating-about-mooring-point frequency varying from zero to high oscillations depending on design and control; this meets the definition of a turbine. Thus a kite system is a fundamental airborne tethered turbine system. Then note that any of the turbines noted in this article could be lifted by kites (kytoon is a type of kite also) and thus form an aerial wind tethered turbine system.

H-rotor

Another type is the H-rotor

Wind belt

Invented by Shawn Frayne. A belt vibrates by the passing flow of air. A magnet is mounted at one end of the belt.

Piezoelectric wind turbines

Another special type of wind turbines are the piezoelectric wind turbines.

Traffic-driven wind generator

A few proposals call for generating power from the otherwise wasted energy in the draft created by traffic.

Blade Tip Power System (BTPS)

Designed by Imad Mahawili with Honeywell/WindTronics. This design uses many nylon blades and turns a permanent magnet generator inside out. The magnets are on the tips of the blades and the stator is on the outside of the generator.

Wind turbine technology used to harness other power sources

Wind turbines may also be used in conjunction with a solar collector to extract the energy due to air heated by the Sun and rising through a large vertical Solar updraft tower. Wind turbines are part of experimental wave powered generators where air displaced by waves drives turbines.

Rooftop wind-turbines

Wind-turbines can be installed on the top of a roof of a building. This is not as common as may first be assumed. Some examples include Marthalen Landi-Silo in Switzerland and Council House 2 in Melbourne, Australia. Discovery Tower is an office building in Houston, Texas, scheduled for opening in 2010, that incorporates 10 wind turbines in its architecture.

The Museum of Science in Boston, Massachusetts began constructing a rooftop Wind Turbine Lab in 2009. The Lab will test nine wind turbines from five different manufacturers on the roof of the Museum. Rooftop wind turbines may suffer from turbulence, especially in cities, which reduces power output and accelerates turbine wear. The lab seeks to address the general lack of performance data for urban wind turbines.^[26]

Due to the structural limitations of buildings, the limited space in urban areas, and safety considerations, wind turbines mounted on buildings are usually small (with nameplate capacities in the low kilowatts), rather than the megawatt-class wind turbines which are most economical for wind farms. A partial exception is the Bahrain World Trade Centre with three 225 kW wind turbines mounted between twin skyscrapers.