Unconventional wind turbines are those that differ significantly from the most common types in use.
As of 2024[update], the most common type ofwind turbine is the three-bladed upwindhorizontal-axis wind turbine (HAWT), where the turbine rotor is at the front of thenacelle and facing the wind upstream of its supportingturbine tower. A second major unit type is thevertical-axis wind turbine (VAWT), with blades extending upwards, supported by a rotating framework.
Due to the large growth of thewind power industry, manywind turbine designs 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.
Nearly all modern wind turbines use rotors with three blades, but some use only two blades. This was the type used atKaiser-Wilhelm-Koog, Germany, where a large experimental two-bladed unit—theGROWIAN, orGroße Windkraftanlage (big wind turbine)—operated from 1983 to 1987. Other prototypes and wind turbine types were manufactured by NedWind. TheEemmeerdijk Wind Park inZeewolde, Netherlands uses only two-bladed turbines. Wind turbines with two blades are manufactured byWindflow Technology,Mingyang Wind Power, GC China Turbine Corp andNordic Windpower.[1] TheNASA wind turbines (1975–1996) each had 2-blade rotors, producing the same energy at lower cost than three-blade rotor designs.
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.
A research project,[2] the ducted rotor consists of a turbine inside a duct that flares at the back. They are also referred asDiffuser-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 bulkygearbox, 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. TheÉolienne Bollée is an example of a DAWT.
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 two rotors separated by twelve feet (3.7 m). It is the most powerful seven-foot-diameter (2.1 m) 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.[3]
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 turbine 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.[4]
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 reducesympathetic vibrations, the two turbines should turn at speeds with few common multiples, for example 7:3 speed ratio.[citation needed]
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 overallpower coefficient of a Counter-rotating horizontal-axis wind turbine may depend by the axial and the radial shift of the rotors[5] and by the rotors' size.[6] As of 2005[update], no large, counter-rotating HAWTs are commercially sold.
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.[7]
De Nolet is a wind turbine in Schiedam disguised as awindmill.
Instead of airplane-inspired wing blades, the design takes after theArchimedean screw turbine, a helix-patterned pipe used in ancient Greece to pump water up from a deeper source.[8][9]
The boundary-layer turbine, orTesla turbine, usesboundary layers instead of blades.
One modern version is the Fuller turbine.[10] 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.
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 wind turbines work by flexingpiezoelectric crystals as they rotate, sufficient to power small electronic devices. They operate with diameters on the scale of 10 centimeters.[11]
Wind turbines may be used in conjunction with asolar collector to extract energy from air heated by the sun and rising through a large vertical updraft tower.
TheVortex Bladeless device maximizesvortex shedding, using thevorticity in wind to flutter a lightweight vertical pole, which delivers that energy to a generator at the bottom of the pole.[12][13][14][15] The design has been criticized for its efficiency of 40%, compared to 70% for conventional designs.[16] 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.[17]
The Saphonian design uses an oscillating dish to drive a piston, which then connects to a generator.[18][19]
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. Costs are low due to low cost components and simple construction.[20]
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.[21][22]
Airborne wind turbines may operate in low or high altitudes; they are part of a wider class of airborne wind energy systems (AWES) addressed byhigh-altitude wind power andcrosswind kite power. Wind turbines could be flown in high-speed winds using high-altitude wind power tactics, taking advantage of high altitude winds.
When the generator is on the ground, then the tethered aircraft need not carry the generator mass or have a conductive tether. When the generator is aloft, then a conductive tether would be used to transmit energy to the ground or used aloft or beamed to receivers using microwave or laser.
For instance, a system of tethered kites[23] could capture energy from high-altitude winds. Another concept uses a helium balloon with attached sails to generate pressure and drive rotation around a horizontal axis. Circular motion of ropes transfer kinetic energy to ground-based generator.[24]
The Gorlov helical turbine (GHT) is a modification of theDarrieus turbine design that useshelical blades/foils.[25][26]
One design uses many nylon blades to run a generator. Its permanent magnets are on the tips of the blades, while thestator is a ring outside the blades.[27]
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.[28]
Revolving-wing wind turbines, or rotating-wing wind turbines, are a category of lift-type vertical-axis wind turbines that use one vertically standing, non-helical airfoil to generate 360-degree rotation around a vertical shaft which runs through the center of the airfoil.
A omnidirectional turbine which uses theBernoulli principle 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 theJames Dyson Award 2018.[29][30]
Airloom is developing a turbine that uses vertical blades that move around an oval track. The system is 25 meters tall. The system is modular: blades can be added and the track length adjusted accordingly. The vendor claimed that thelevelized cost of electricity is one-third of conventional turbines. The design is a terrestrial equivalent of an airborne turbine whose trajectory is fixed. A system can be installed and operating within one day.[31]
SheerWind's INVELOX technology was developed by Daryoush Allaei. A large funnel-shaped intake acts as a wind concentrator, which ends in aVenturi section. Wind exits from a diffuser; turbines are placed inside the Venturi section. 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.[32][33] The device has been constructed and tested, but has been criticized for lack of efficiency.[34] As of 2017[update], prototypes are being installed.[35][36]
Wind-turbines can be installed on building roofs. Examples includeMarthalen Landi-Silo in Switzerland,Council House 2 inMelbourne,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 inHouston,Texas, that incorporates ten wind turbines.
TheMuseum of Science inBoston, Massachusetts began constructing a rooftop Wind Turbine Lab in 2009.[37] 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.[38] The lab seeks to address the general lack of performance data for urban wind turbines.[37]
Due to structural limitations of buildings, limited space in urban areas, and safety considerations, building turbines are usually small (with capacities in the lowkilowatts). An exception is theBahrain World Trade Centre with three 225 kW wind turbines mounted between twin skyscrapers.
Proposals call for generating power from the energy in the draft created by traffic.[39][40]
Some installations have installed visitor centers on turbine bases, or by providing viewing areas.[41] The wind turbines themselves are generally of conventional design, while serving the unconventional roles of technology demonstration, public relations, and education.
