Unconventional wind turbines

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Counter rotating wind turbines Offshore wind farm.gif
Counter rotating wind turbines
Light pole wind turbine Light pole wind turbine.gif
Light pole wind turbine

Unconventional wind turbines are those that differ significantly from the most common types in use.

Contents

As of 2012, the most common type of wind turbine is the three-bladed upwind horizontal-axis wind turbine (HAWT), where the turbine rotor is at the front of the nacelle 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, many wind 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.

Crosswind kite generator with fast motion transfer. Crosswind kite power station with fast motion transfer having two wings offshore.jpg
Crosswind kite generator with fast motion transfer.

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. [1] 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, [2] 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, 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 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 7-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]

Counter rotating wind turbine Counter rotating wind turbine animation.gif
Counter rotating wind turbine

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. [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 reduce sympathetic 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 overall power 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, 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 [7]

Wind-mill style

De Nolet is a wind turbine in Schiedam disguised as a windmill.

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. [8] [9]

Bladeless

Boundary layer

The boundary layer or Tesla turbine uses boundary 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.

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 crystals as they rotate, sufficient to power small electronic devices. They operate with diameters on the scale of 10 centimeters. [11]

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, using the vorticity 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]

Saphonian

The Saphonian design uses an oscillating dish to drive a piston, which then connects to a generator. [18] [19]

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 ducts). Costs are low due to low cost components and simple construction. [20]

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. [21] [22]

Aerial

Concept for an airborne wind generator Airborne wind generator-en.svg
Concept for an airborne wind generator

Airborne wind turbines may operate in low or high altitudes; they are part of a wider class of Airborne Wind Energy Systems (AWES) addressed by high-altitude wind power and crosswind 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.

The principle of the kite airborne wind turbine. Image source: Kitesforfuture Principle of kite energy.png
The principle of the kite airborne wind turbine. Image source: Kitesforfuture
A possible flight path of the kite airborne wind turbine. Image source: Kitesforfuture KiteEight.png
A possible flight path of the kite airborne wind turbine. Image source: Kitesforfuture

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]

Vertical

Vertical axis wind turbines offshore Vertical axis wind turbine offshore.gif
Vertical axis wind turbines offshore

Gorlov

The Gorlov helical turbine (GHT) is a modification of the Darrieus turbine design that uses helical blades/foils. [25] [26]

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 is a ring outside the blades. [27]

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. [28]

Revolving Wing VAWT Wind Turbine

Revolving Wing Wind Turbines or Rotating Wing Wind Turbines are a new category of lift-type Vertical Axis Wind Turbines (VAWT) which use 1 vertically standing, non-helical airfoil to generate 360 degree rotation around a vertical shaft which runs through the center of the airfoil.

O-Wind turbine

A omnidirectional turbine which uses the Bernoulli 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 the James Dyson Award 2018. [29] [30]

Revolving blade

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 the levelized 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]

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. [32] [33] The device has been constructed and tested, but has been criticized for lack of efficiency. [34] As of 2017, prototypes are being installed. [35] [36]

Applications

Rooftop

Wind-turbines can be installed on building roofs. Examples include Marthalen Landi-Silo in Switzerland, Council House 2 in Melbourne, 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, Texas, that incorporates 10 wind turbines.

The Museum of Science in Boston, 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 low kilowatts). An exception is the Bahrain World Trade Centre with three 225 kW wind turbines mounted between twin skyscrapers.

Traffic-driven

Highway wind turbine Highway wind turbine.gif
Highway wind turbine

Proposals call for generating power from the energy in the draft created by traffic. [39] [40]

Education

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.

See also

Related Research Articles

<span class="mw-page-title-main">Turbine</span> Rotary mechanical device that extracts energy from a fluid flow

A turbine is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced can be used for generating electrical power when combined with a generator. A turbine is a turbomachine with at least one moving part called a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. Early turbine examples are windmills and waterwheels.

<span class="mw-page-title-main">Windpump</span> A windmill for pumping water

A windpump is a wind-driven device which is used for pumping water.

<span class="mw-page-title-main">Darrieus wind turbine</span> Type of vertical axis wind turbine

The Darrieus wind turbine is a type of vertical axis wind turbine (VAWT) used to generate electricity from wind energy. The turbine consists of a number of curved aerofoil blades mounted on a rotating shaft or framework. The curvature of the blades allows the blade to be stressed only in tension at high rotating speeds. There are several closely related wind turbines that use straight blades. This design of the turbine was patented by Georges Jean Marie Darrieus, a French aeronautical engineer; filing for the patent was October 1, 1926. There are major difficulties in protecting the Darrieus turbine from extreme wind conditions and in making it self-starting.

<span class="mw-page-title-main">Enercon</span>

Enercon GmbH is a wind turbine manufacturer based in Aurich, Lower Saxony, Germany. It has been the market leader in Germany since the mid-1990s. Enercon has production facilities in Germany, Brazil, India, Canada, Turkey and Portugal. In June 2010, Enercon announced that they would be setting up Irish headquarters in Tralee.

<span class="mw-page-title-main">Savonius wind turbine</span> Type of wind turbine that spins along its vertical axis

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 rotating shaft or framework, either ground stationed or tethered in airborne systems.

<span class="mw-page-title-main">Yaw drive</span>

The yaw drive is an important component of the horizontal axis wind turbines' yaw system. To ensure the wind turbine is producing the maximal amount of electric energy at all times, the yaw drive is used to keep the rotor facing into the wind as the wind direction changes. This only applies for wind turbines with a horizontal axis rotor. The wind turbine is said to have a yaw error if the rotor is not aligned to the wind. A yaw error implies that a lower share of the energy in the wind will be running through the rotor area..

<span class="mw-page-title-main">Tail rotor</span>

The tail rotor is a smaller rotor mounted vertically or near-vertically at the tail of a traditional single-rotor helicopter, where it rotates to generate a propeller-like horizontal thrust in the same direction as the main rotor's rotation. The tail rotor's position and distance from the helicopter's center of mass allow it to develop enough thrust leverage to counter the reactional torque exerted on the fuselage by the spinning of the main rotor. Without the tail rotor or other anti-torque mechanisms, the helicopter would be constantly spinning in the opposite direction of the main rotor when flying.

<span class="mw-page-title-main">Airborne wind turbine</span> High-altitude flying turbine for generating electricity

An airborne wind turbine is a design concept for a wind turbine with a rotor supported in the air without a tower, thus benefiting from the higher velocity and persistence of wind at high altitudes, while avoiding the expense of tower construction, or the need for slip rings or yaw mechanism. An electrical generator may be on the ground or airborne. Challenges include safely suspending and maintaining turbines hundreds of meters off the ground in high winds and storms, transferring the harvested and/or generated power back to earth, and interference with aviation.

<span class="mw-page-title-main">Turby wind turbine</span> Brand of vertical-axis Darrieus wind turbine

The Turby is a brand of vertical-axis Darrieus wind turbine. The three vertical aerofoil blades have a helical twist of 60 degrees, similar to Gorlov's water turbines.

<span class="mw-page-title-main">Coaxial-rotor aircraft</span> Helicopter with two sets of rotor blades placed on top of each other

A coaxial-rotor aircraft is an aircraft whose rotors are mounted one above the other on concentric shafts, with the same axis of rotation, but turning in opposite directions (contra-rotating).

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 tower.

<span class="mw-page-title-main">Gorlov helical turbine</span> Water turbine

The Gorlov helical turbine (GHT) is a water turbine evolved from the Darrieus turbine design by altering it to have helical blades/foils. Water turbines take kinetic energy and translates it into electricity. It was patented in a series of patents from September 19, 1995 to July 3, 2001 and won 2001 ASME Thomas A. Edison. GHT was invented by Alexander M. Gorlov, professor of Northeastern University.

<span class="mw-page-title-main">Wind turbine design</span> Process of defining the form of wind turbine systems

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 mechanical rotation into electrical power, and other systems to start, stop, and control the turbine.

<span class="mw-page-title-main">History of wind power</span>

Wind power has been used as long as humans have put sails into the wind. King Hammurabi's Codex already mentioned windmills for generating mechanical energy. Wind-powered machines used to grind grain and pump water — the windmill and wind pump — were developed in what is now Iran, Afghanistan, and Pakistan by the 9th century. Wind power was widely available and not confined to the banks of fast-flowing streams, or later, requiring sources of fuel. Wind-powered pumps drained the polders of the Netherlands, and in arid regions such as the American midwest or the Australian outback, wind pumps provided water for livestock and steam engines.

<span class="mw-page-title-main">Wind turbine</span> Machine that converts wind energy into electrical energy

A wind turbine is a device that converts the kinetic energy of wind into electrical energy. As of 2020, hundreds of thousands of large turbines, in installations known as wind farms, were generating over 650 gigawatts of power, with 60 GW added each year. Wind turbines are an increasingly important source of intermittent renewable energy, and are used in many countries to lower energy costs and reduce reliance on fossil fuels. One study claimed that, as of 2009, wind had the "lowest relative greenhouse gas emissions, the least water consumption demands and the most favorable social impacts" compared to photovoltaic, hydro, geothermal, coal and gas energy sources.

<span class="mw-page-title-main">Yaw system</span>

The yaw system of wind turbines is the component responsible for the orientation of the wind turbine rotor towards the wind.

<span class="mw-page-title-main">Tidal stream generator</span> Type of tidal power generation technology

A tidal stream generator, often referred to as a tidal energy converter (TEC), is a machine that extracts energy from moving masses of water, in particular tides, although the term is often used in reference to machines designed to extract energy from the run of a river or tidal estuarine sites. Certain types of these machines function very much like underwater wind turbines and are thus often referred to as tidal turbines. They were first conceived in the 1970s during the oil crisis.

<span class="mw-page-title-main">Crosswind kite power</span> Form of wind-powered mechanical or electrical generation

Crosswind kite power is power derived from airborne wind-energy conversion systems or crosswind kite power systems (CWKPS). The kite system is characterized by energy-harvesting parts flying transverse to the direction of the ambient wind, i.e., to crosswind mode; sometimes the entire wing set and tether set is flown in crosswind mode. From toy to power-grid-feeding sizes, these systems may be used as high-altitude wind power (HAWP) devices or low-altitude wind power (LAWP) devices without having to use towers. Flexible wings or rigid wings may be used in the kite system. A tethered wing, flying in crosswind at many times wind speed, harvests wind power from an area that exceeds the wing's total area by many times.

Vortex Bladeless Ltd. is a Spanish technology startup company that is developing a specific type of wind power generator that does not utilize rotating blades or lubricants, which more common wind turbines do use. Power instead is produced from resonant vibrations when wind passes through the turbine and is deflected into vortices in a process called vortex shedding.

<span class="mw-page-title-main">Vertical-axis wind turbine</span> Type of wind turbine

A vertical-axis wind turbine (VAWT) is a type of wind turbine where the main rotor shaft is set transverse to the wind while the main components are located at the base of the turbine. This arrangement allows the generator and gearbox to be located close to the ground, facilitating service and repair. VAWTs do not need to be pointed into the wind, which removes the need for wind-sensing and orientation mechanisms. Major drawbacks for the early designs included the significant torque ripple during each revolution, and the large bending moments on the blades. Later designs addressed the torque ripple by sweeping the blades helically. Savonius vertical-axis wind turbines (VAWT) are not widespread, but their simplicity and better performance in disturbed flow-fields, compared to small horizontal-axis wind turbines (HAWT) make them a good alternative for distributed generation devices in an urban environment.

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