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Unconventional wind turbines are those that differ significantly from the most common types in use. , the most common type of
wind turbine A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each year ...
is the three-bladed upwind
horizontal-axis wind turbine A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each year. W ...
(HAWT), where the turbine rotor is at the front of the
nacelle A nacelle ( ) is a "streamlined body, sized according to what it contains", such as an engine, fuel, or equipment on an aircraft. When attached by a pylon entirely outside the airframe, it is sometimes called a pod, in which case it is attached ...
and facing the wind upstream of its supporting turbine tower. A second major unit type is the vertical-axis wind turbine (VAWT), with blades extending upwards, supported by a rotating framework. Due to the large growth of the
wind power industry The wind power industry is involved with the design, manufacture, construction, and maintenance of wind turbines. The modern wind power industry began in 1979 with the serial production of wind turbines by Danish manufacturers. The industry is un ...
, many
wind turbine design Wind turbine design is the process of defining the form and configuration of a wind turbine to extract energy from the wind. An installation consists of the systems needed to capture the wind's energy, point the turbine into the wind, convert ...
s exist, are in development, or have been proposed. The variety of designs reflects ongoing commercial, technological, and inventive interests in harvesting wind resources more efficiently and in greater volume. Some unconventional designs have entered commercial use, while others have only been demonstrated or are only theoretical concepts. Unconventional designs cover a wide gamut of innovations, including different rotor types, basic functionalities, supporting structures and form-factors.


Horizontal axis


Twin-bladed rotor

Nearly all modern wind turbines use rotors with three blades, but some use only two blades. This was the type used at Kaiser-Wilhelm-Koog, Germany, where a large experimental two-bladed unit—the GROWIAN, or ''Große Windkraftanlage'' (big wind turbine)—operated from 1983 to 1987. Other prototypes and wind turbine types were manufactured by NedWind. The Eemmeerdijk Wind Park in Zeewolde, Netherlands uses only two-bladed turbines. Wind turbines with two blades are manufactured by Windflow Technology, Mingyang Wind Power, GC China Turbine Corp and Nordic Windpower,. The NASA wind turbines (1975-1996) each had 2-blade rotors, producing the same energy at lower cost than three-blade rotor designs.


Downwind rotor

Nearly all wind turbines place the rotor in front of the nacelle when the wind is blowing (upwind design). Some turbines place the rotor behind the nacelle (downwind design). This design has the advantage that the turbine can be made to passively align itself with the wind, reducing cost. The main drawback is that the load on the blades changes as they pass behind the tower, increasing fatigue loading, and potentially exciting resonances in other turbine structures.


Ducted rotor

A research project, the ducted rotor consists of a turbine inside a duct that flares at the back. They are also referred as Diffuser-Augmented Wind Turbines (i.e. DAWT). Its main advantage 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 Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), differ ...
, allowing the mechanical portion to be smaller and lighter. A disadvantage is that (apart from the gearbox) it is more complicated than the unducted rotor and the duct's weight increases tower weight. The
Éolienne Bollée The Éolienne Bollée is an unusual wind turbine, unique for having a stator and a rotor, as a water turbine has. The eponymous invention was first patented in 1868 by Ernest Sylvain Bollée in France. A further patent dated 1885 differed mainly ...
is an example of a DAWT.


Co-axial, multi-rotor

Two or more rotors may be mounted to a single 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 was multiplied several times using co-axial, multiple rotors in testing conducted by inventor and researcher Douglas Selsam 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 turbine available, due to this extra rotor. In 2015, Iowa State University aerospace engineers Hui Hu and Anupam Sharma were optimizing designs of multi-rotor systems, including a horizontal-axis co-axial dual-rotor model. In addition to a conventional three-blade rotor, it has a smaller secondary three-blade rotor, covering the near-axis region usually inefficiently harvested. Preliminary results indicated 10-20% gains, less efficient than is claimed by existing counter-rotating designs.


Counter-rotating horizontal-axis

When a system expels or accelerates mass in one direction, the accelerated mass causes a proportional but opposite force on that system. The spinning blade of a single rotor wind turbine causes a significant amount of tangential or rotational air flow. The energy of this tangential air flow is wasted in a single-rotor propeller design. To use this wasted effort, the placement of a second rotor behind the first takes advantage of the disturbed airflow, and can gain up to 40% more energy from a given swept area as compared with a single rotor. Other advantages of contra-rotation include no gear boxes and auto-centering on the wind (no yaw motors/mechanism required). A patent application dated 1992 exists based on work done with the Trimblemill. 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. When land or sea area for a second wind turbine does not come at a premium the 40% gain with a second rotor has to be compared with a 100% gain via the expense of a separate foundation and tower with cabling for the second turbine. The overall power coefficient of a Counter-rotating horizontal-axis wind turbine may depend by the axial and the radial shift of the rotors and by the rotors' size. , no large, counter-rotating HAWTs are commercially sold.


Furling tail and twisting blades

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 efficiency and be used in "do-it-yourself" construction


Wind-mill style

De Nolet is a wind turbine in Schiedam disguised as a
windmill A windmill is a structure that converts wind power into rotational energy using vanes called sails or blades, specifically to mill grain (gristmills), but the term is also extended to windpumps, wind turbines, and other applications, in some p ...
.


Archimedean screw

Instead of airplane-inspired wing blades, the design takes after the Archimedean screw turbine, a helix-patterned pipe used in ancient Greece to pump water up from a deeper source.


Telescopic Wind Turbine Blades

Energy Unlimited built and ran wind turbines with telescopic wind turbine blades. They were called "Variblades" Telescopic blades can change length to give you a large rotor or a small rotor. This allows you to produce more power in less than rated wind speeds and to reduce loads in high winds. These blades were some of the most advanced wind turbine blades ever built. https://ieeexplore.ieee.org/document/1489577 https://digital.library.unt.edu/ark:/67531/metadc786056/m2/1/high_res_d/841190.pdf


Bladeless


Boundary layer

The boundary layer or
Tesla turbine Tesla turbine at Nikola Tesla Museum The Tesla turbine is a bladeless centripetal flow turbine patented by Nikola Tesla in 1913. It is referred to as a ''bladeless turbine''. The Tesla turbine also known as the ''boundary-layer turbine'', '' ...
uses
boundary layer In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces a no-slip boundary condi ...
s instead of blades. One modern version is the Fuller turbine. The concept is similar to a stack of disks on a central shaft, separated by a small air gap. The surface tension of air in the small gaps creates friction, rotating the disks around the shaft. Vanes direct the air for improved performance, hence it is not strictly bladeless.


Vaneless ion wind generator

A vaneless ion wind generator is a theoretical device that produces electrical energy by using the wind to move electric charge from one electrode to another.


Piezoelectric

Piezoelectric wind turbines work by flexing
piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word ''p ...
crystals as they rotate, sufficient to power small electronic devices. They operate with diameters on the scale of 10 centimeters.


Solar updraft tower

Wind turbines may be used in conjunction with a solar collector to extract energy from air heated by the sun and rising through a large vertical updraft tower.


Vortex

The Vortex Bladeless device maximizes
vortex shedding In fluid dynamics, vortex shedding is an oscillating flow that takes place when a fluid such as air or water flows past a bluff (as opposed to streamlined) body at certain velocities, depending on the size and shape of the body. In this flow, v ...
, using the
vorticity In continuum mechanics, vorticity is a pseudovector field that describes the local spinning motion of a continuum near some point (the tendency of something to rotate), as would be seen by an observer located at that point and traveling along wi ...
in wind to flutter a lightweight vertical pole, which delivers that energy to a generator at the bottom of the pole. The design has been criticized for its efficiency of 40%, compared to 70% for conventional designs. However, individual poles can be placed more closely together, offsetting the losses. The design avoids mechanical components, lowering costs. The system also does not threaten bird life and operates silently.


Saphonian

The Saphonian design uses an oscillating dish to drive a piston, which then connects to a generator.


Windbeam

The Windbeam generator consists of a beam suspended by springs within an outer frame. The beam oscillates rapidly when exposed to airflow due to multiple fluid flow phenomena. A linear alternator converts the beam motion. The absence of bearings and gears eliminates frictional inefficiencies and noise. The generator can operate in low-light environments unsuitable for solar panels (e.g.
HVAC Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. ...
ducts). Costs are low due to low cost components and simple construction.


Wind belt

Windbelt is a flexible, tensioned belt that vibrates from the passing flow of air, due to aeroelastic flutter. A magnet, mounted at one end of the belt oscillates in and out of coiled windings, producing electricity. The inventor is Shawn Frayne.


Aerial

Wind turbines could be flown in high-speed winds using
high altitude wind power Airborne wind energy (AWE) is the direct use or generation of wind energy by the use of aerodynamic or aerostatic lift devices. AWE technology is able to harvest high altitude winds, in contrast to wind turbines, which use a rotor mounted on a to ...
tactics, taking advantage of high altitude winds. A system of tethered kites could capture energy from high-altitude winds.


Vertical


Gorlov

The Gorlov helical turbine (GHT) is a modification of the Darrieus turbine design that uses
helical Helical may refer to: * Helix A helix () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is for ...
blades/foils.


Enclosed blades

One design uses many nylon blades to run a generator. Its permanent magnets are on the tips of the blades, while the
stator The stator is the stationary part of a rotary system, found in electric generators, electric motors, sirens, mud motors or biological rotors. Energy flows through a stator to or from the rotating component of the system. In an electric mot ...
is a ring outside the blades.


H-rotor

The giromill is a vertical axis turbine that rotates one blade in one direction while another moves in the opposite direction. Consequently, only one blade is working at a time. Its efficiency is low.


O-Wind turbine

A omnidirectional turbine which uses the
Bernoulli principle In fluid dynamics, Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid's potential energy. The principle is named after the Swiss mathematic ...
to generate energy using wind from any direction. The design is spherical with a number of ducts across the surface, a pressure difference causes the rotation. The design won the James Dyson Award 2018.


Components


INVELOX

SheerWind's INVELOX technology was developed by Dr. Daryoush Allaei. The invention captures and delivers wind to a turbine. In a sense, INVELOX is a wind injection system, much like a fuel injection system for cars. It works by accelerating the wind. A large intake captures wind and funnels it to a concentrator that ends in a Venturi section and finally wind exits from a diffuser. Turbine(s) are placed inside the Venturi section of the INVELOX. Inside the Venturi the dynamic pressure is high while the static pressure is low. The Turbine converts dynamic pressure or kinetic energy to mechanical rotation and thereby to electrical power using a generator. The device has been constructed and tested, but has been criticized for lack of efficiency. , prototypes are being installed.


Applications


Rooftop

Wind-turbines can be installed on building roofs. Examples include Marthalen Landi-Silo in Switzerland, Council House 2 in
Melbourne Melbourne ( ; Boonwurrung/Woiwurrung: ''Narrm'' or ''Naarm'') is the capital and most populous city of the Australian state of Victoria, and the second-most populous city in both Australia and Oceania. Its name generally refers to a metr ...
, Australia. Ridgeblade in the UK is a vertical wind turbine on its side mounted on the apex of a pitched roof. Another example installed in France is the Aeolta AeroCube. Discovery Tower is an office building in
Houston Houston (; ) is the List of cities in Texas by population, most populous city in Texas, the Southern United States#Major cities, most populous city in the Southern United States, the List of United States cities by population, fourth-most pop ...
,
Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
, that incorporates 10 wind turbines. The Museum of Science in Boston, Massachusetts began constructing a rooftop Wind Turbine Lab in 2009. The lab is testing nine wind turbines from five different manufacturers. 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. Due to structural limitations of buildings, limited space in urban areas, and safety considerations, building turbines are usually small (with capacities in the low
kilowatt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wat ...
s). An exception is the
Bahrain World Trade Centre The Bahrain World Trade Center (also called Bahrain WTC or BWTC) is a , 50-floor, twin tower complex located in Manama, Bahrain. Designed by the multi-national architectural firm Atkins, construction on the towers was completed in 2008. It is th ...
with three 225 kW wind turbines mounted between twin skyscrapers.


Traffic-driven

Proposals call for generating power from the energy in the draft created by traffic.


Education

Some installations have installed visitor centers on turbine bases, or by providing viewing areas. The wind turbines themselves are generally of conventional design, while serving the unconventional roles of technology demonstration, public relations, and education.


See also

* EWICON *
Compact wind acceleration turbine Compact Wind Acceleration Turbines (CWATs) are a class of wind turbine that uses structures to accelerate wind before it enters the wind-generating element. The concept of these structures has been around for decades but has not gained wide accep ...
* Crosswind Kite Power *
Savonius wind turbine Savonius wind turbines are a type of vertical-axis wind turbine (VAWT), used for converting the force of the wind into torque on a rotating shaft. The turbine consists of a number of aerofoils, usually—but not always—vertically mounted on a ...
* Vertical-axis wind turbine *
Wind lens The wind lens is a modification on the wind turbine created by Professor Ohya from the Kyushu University as an attempt to be more efficient in production of electricity and less invasive to both humans and nature. While still in progress, the win ...
* Unconventional oil * Unconventional gas


References

{{Wind power Chinese inventions Wind power Wind turbines