Airborne wind energy

Last updated

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.

Contents

The term high-altitude wind power (HAWP) has been used to refer to AWE systems. [1] However, semantically HAWP might also include wind energy conversion systems that are somehow positioned at a large height from the ground or sea surface.

Various mechanisms are proposed for capturing the kinetic energy of winds such as kites, kytoons, aerostats, gliders, gliders with turbines for regenerative soaring, [2] sailplanes with turbines, or other airfoils, including multiple-point building- or terrain-enabled holdings. [3] Once the mechanical energy is derived from the wind's kinetic energy, then many options are available for using that mechanical energy: direct traction, [4] [5] conversion to electricity aloft or at ground station, conversion to laser or microwave for power beaming to other aircraft or ground receivers. Energy generated by a high-altitude system may be used aloft or sent to the ground surface by conducting cables, mechanical force through a tether, rotation of endless line loop, movement of changed chemicals, flow of high-pressure gases, flow of low-pressure gases, or laser or microwave power beams.

High-altitude wind for power purposes

Winds at higher altitudes become steadier, more persistent, and of higher velocity. Because power available in wind increases as the cube of velocity (the velocity-cubed law), [6] [7] assuming other parameters remaining the same, doubling a wind's velocity gives 23=8 times the power; tripling the velocity gives 33=27 times the available power. With steadier and more predictable winds, high-altitude wind has an advantage over wind near the ground. Being able to locate HAWP to effective altitudes and using the vertical dimension of airspace for wind farming brings further advantage using high-altitude winds for generating energy.

High-altitude wind generators can be adjusted in height and position to maximize energy return, which is impractical with fixed tower-mounted wind generators.

In each range of altitudes there are altitude-specific concerns being addressed by researchers and developers. As altitude increases, tethers increase in length, the temperature of the air changes, and vulnerability to atmospheric lightning changes. With increasing altitude, exposure to liabilities increase, costs increase, turbulence exposure changes, likelihood of having the system fly in more than one directional strata of winds increases, and the costs of operation changes. HAWP systems that are flown must climb through all intermediate altitudes up to final working altitudes—being at first a low- and then a high- altitude device.

An atlas of the high-altitude wind power resource has been prepared for all points on Earth. [8] A similar atlas of global assessment [9] was developed at Joby Energy.

Methods of capturing kinetic energy of high-altitude winds

Energy can be captured from the wind by kites, [10] kytoons, tethered gliders, [11] tethered sailplanes, aerostats (spherical as well as shaped kytoons), bladed turbines, airfoils, airfoil matrices, drogues, variable drogues, spiral airfoils, Darrieus turbines, Magnus-effect VAWT blimps, multiple-rotor complexes, fabric Jalbert-parafoil kites, uni-blade turbines, flipwings, tethers, bridles, string loops, wafting blades, undulating forms, and piezoelectric materials, [12] and more. [13]

When a scheme's purpose is to propel ships and boats, [14] [15] the objects tether-placed in the wind will tend to have most of the captured energy be in useful tension in the main tether. The aloft working bodies will be operated to maintain useful tension even while the ship is moving. This is the method for powerkiting sports. This sector of HAWP is the most installed method. Folklore suggests that Benjamin Franklin used the traction method of HAWP. George Pocock was a leader in tugging vehicles by traction. [16]

Controls

HAWP aircraft need to be controlled. Solutions in built systems have control mechanisms variously situated. Some systems are passive, or active, or a mix. When a kite steering unit (KSU) is lofted, the KSU may be robotic and self-contained; a KSU may be operated from the ground via radio-control by a live human operator or by smart computer programs. Some systems have built sensors in the aircraft body that report parameters like position, relative position to other parts. Kite control units (KCU) have involved more than steering; tether reeling speeds and directions can be adjusted in response to tether tensions and needs of the system during a power-generating phase or return-non-power-generating phase. Kite control parts vary widely. [17] [18]

Methods of converting the energy

The mechanical energy of the device may be converted to heat, sound, electricity, light, tension, pushes, pulls, laser, microwave, chemical changes, or compression of gases. Traction is a big direct use of the mechanical energy as in tugging cargo ships and kiteboarders. There are several methods of getting the mechanical energy from the wind's kinetic energy. Lighter-than-air (LTA) moored aerostats are employed as lifters of turbines. Heavier-than-air (HTA) tethered airfoils are being used as lifters or turbines themselves. Combinations of LTA and HTA devices in one system are being built and flown to capture HAWP. Even a family of free-flight airborne devices are represented in the literature that capture the kinetic energy of high-altitude winds (beginning with a description in 1967 by Richard Miller in his book Without Visible Means of Support) and a contemporary patent application by Dale C. Kramer, soaring sailplane competitor, inventor.

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

A research on airborne wind turbine technology innovations reveals that the “Kite type AWTs” technique, the most common type, has high scope of growth in the future; it has contributed for about 44% of the total airborne wind energy during 2008–2012. The kite type AWTs extract energy through wind turbines suspended at high altitudes using kites such as multi-tethered kite, kite and dual purpose circular fan, rotary wing kites etc. [19]

Electric generator position in a HAWP system

Electricity generation is just one of the options for capturing mechanical energy; however, this option dominates the focus of professionals aiming to supply large amounts of energy to commerce and utilities. A long array of secondary options include tugging water turbines, pumping of water, or compressing air or hydrogen. The position of the electric generator is a distinguishing feature among systems. Flying the generator aloft is done in a variety of ways. Keeping the generator at the mooring region is another large design option. The option in one system of a generator aloft and at the ground station has been used where a small generator operates electronic devices aloft while the ground generator is the big worker to make electricity for significant loads.

The “Carousel” configuration several kites fly at a constant height and higher altitudes, pulling in rotation a generator that moves on a wide circular rail. For a large Carousel system, the power obtained can be calculated as of the order of GW, exposing a law that see the power attainable as a function of the diameter raised to the fifth power, while the increment of cost of the generator is linear. [20]

Aerostat-based HAWP

One method of keeping working HAWP systems aloft is to use buoyant aerostats whether or not the electric generator is lifted or left on the ground. The aerostats are usually, but not always, shaped to achieve a kiting lifting effect. Recharging leaked lifting gas receives various solutions. In case of productive winds the aerostats are typically blown down by the aerodynamic drag applied on the wide and unavoidable Reynolds surface excluding them de facto from the HAWP category.

Non-airborne systems

Conceptually, two adjacent mountains (natural or terrain-enabled) or artificial buildings or towers (urban or artificial) could have a wind turbine suspended between them by use of cables. When HAWP is cabled between two mountain tops across a valley, [3] the HAWP device is not airborne, but borne up by the cable system. No such systems are known to be in use, though patents teach these methods. When non-cabled bridges are the foundation for holding wind turbines high above the ground, [29] then these are grouped with conventional towered turbines and are outside the intent of HAWP where the tethering an airborne system is foundational.

Safety

Lightning, aircraft traffic, emergency procedures, system inspections, visibility marking of system parts and its tethers, electrical safety, runaway-wing procedures, over-powering controls, appropriate mooring, and more form the safety environment for HAWP systems.

Challenges as an emerging industry

There have been several periods of high interest in HAWP before the contemporary activity. The first period had a high focus on pulling carriages over the lands and capturing atmospheric electricity and lightning for human use. [30] The second period was in the 1970s and 1980s when research and investment flourished; a drop in oil price resulted in no significant installations of HAWP. Return on investment (ROI) has been the key parameter; that ROI remains in focus in the current development activity while in the background is the renewable and sustainable energy movement supporting wind power of any kind; but HAWP must compete on ROI with conventional towered solutions. A test center at Lista, Norway provides independent verification of research. [31]

Early references to HAWP

Early centuries of kiting demonstrated that the kite is a rotary engine that rotates its tether part about its mooring point and causes hands and arms to move because of the energy captured from higher winds into the mechanical device. The tension in the lofted devices performs the work of lifting and pulling body parts and things. Airborne wind energy (AWE) for HAWP was birthed thousands of years ago; naming what happened and developing the implied potentials of tethered aircraft for doing special works is what is occurring in AWE HAWP. What is "low" for some workers is "high" for others.

Autorotation

Autorotation is the basis of a large sector of AWE technology. High altitude wind power research and development centers frequently are dependent on blade autorotation: SkyMill Energy, Joby Energy, Sky Windpower, BaseLoad Energy, Magenn Power, and Makani Power are making and testing airborne wind energy conversion systems (AWECS) that employ autorotation of blades to drive the shafts of generators to make electricity at altitude and send the electricity to earth via conductive tethers. [41]

See also

Related Research Articles

<span class="mw-page-title-main">Aircraft</span> Vehicle or machine that is able to fly by gaining support from the air

An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or the dynamic lift of an airfoil, or, in a few cases, direct downward thrust from its engines. Common examples of aircraft include airplanes, helicopters, airships, gliders, paramotors, and hot air balloons.

<span class="mw-page-title-main">Unpowered aircraft</span> Aerial vehicle capable of sustaining flight without onboard propulsion

Unpowered aircraft can remain airborne for a significant period of time without onboard propulsion. They can be classified as gliders, lighter-than-air balloons and tethered kites. In the case of kites, lift is obtained by tethering to a fixed or moving object, perhaps another kite, to obtain a flow of wind over the lifting surfaces. In the case of balloons, lift is obtained through inherent buoyancy and the balloon may or may not be tethered. Free balloon flight has little directional control. Gliding aircraft include sailplanes, hang gliders, and paragliders that have full directional control in free flight.

<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.

For fixed-wing aircraft, autorotation is the tendency of an aircraft in or near a stall to roll spontaneously to the right or left, leading to a spin.

<span class="mw-page-title-main">Aerostat</span> Lighter-than-air aircraft

An aerostat is a lighter-than-air aircraft that gains its lift through the use of a buoyant gas. Aerostats include unpowered balloons and powered airships. A balloon may be free-flying or tethered. The average density of the craft is lower than the density of atmospheric air, because its main component is one or more gasbags, a lightweight skin containing a lifting gas to provide buoyancy, to which other components such as a gondola containing equipment or people are attached. Especially with airships, the gasbags are often protected by an outer envelope.

<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">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">Allsopp Helikite</span>

The Allsopp Helikite is a type of kite-balloon or kytoon designed by Sandy Allsopp in the United Kingdom in 1993. This Helikite comprises a combination of a helium balloon and a kite to form a single, aerodynamically sound, tethered aircraft, that utilises both wind and helium for its lift.

<span class="mw-page-title-main">Unconventional wind turbines</span> Wind turbines of unconventional design

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

A laddermill kite system is an airborne wind turbine consisting of a long string or loop of power kites. The loop or string of kites would be launched in the air by the lifting force of the kites, until it is fully unrolled, and the top reaches a height determined by designers and operators; some designers have considered heights of about 30,000 feet, but the concept is not height-dependent. The laddermill method may use one endless loop, two endless loops, or more such loops.

SkySails Group GmbH is a Hamburg-based company that sells kite rigs to propel cargo ships, large yachts and fishing vessels by wind energy as well as airborne wind energy systems for electricity production from high-altitude winds.

<span class="mw-page-title-main">Wind-powered vehicle</span> Vehicle propelled by wind

Wind-powered vehicles derive their power from sails, kites or rotors and ride on wheels—which may be linked to a wind-powered rotor—or runners. Whether powered by sail, kite or rotor, these vehicles share a common trait: As the vehicle increases in speed, the advancing airfoil encounters an increasing apparent wind at an angle of attack that is increasingly smaller. At the same time, such vehicles are subject to relatively low forward resistance, compared with traditional sailing craft. As a result, such vehicles are often capable of speeds exceeding that of the wind.

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

A kytoon or kite balloon is a tethered aircraft which obtains some of its lift dynamically as a heavier-than-air kite and the rest aerostatically as a lighter-than-air balloon. The word is a portmanteau of kite and balloon.

<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.

Makani Technologies LLC was an Alameda, California-based company that developed airborne wind turbines. Founded in 2006, Makani was acquired by Google in May 2013. In February 2020, Makani was shut down by Alphabet, Google's parent company.

<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.

Oscillating water columns (OWCs) are a type of wave energy converter that harness energy from the oscillation of the seawater inside a chamber or hollow caused by the action of waves. OWCs have shown promise as a renewable energy source with low environmental impact. Because of this, multiple companies have been working to design increasingly efficient OWC models. OWC are devices with a semi-submerged chamber or hollow open to the sea below, keeping a trapped air pocket above a water column. Waves force the column to act like a piston, moving up and down, forcing the air out of the chamber and back into it. This continuous movement forces a bidirectional stream of high-velocity air, which is channeled through a power take-off (PTO). The PTO system converts the airflow into energy. In models that convert airflow to electricity, the PTO system consists of a bidirectional turbine. This means that the turbine always spins the same direction regardless of the direction of airflow, allowing for energy to be continuously generated. Both the collecting chamber and PTO systems will be explained further under "Basic OWC Components."

Kitepower is a registered trademark of the Dutch company Enevate B.V. developing mobile airborne wind power systems. Kitepower was founded in 2016 by Johannes Peschel and Roland Schmehl as a university spin-off from the Delft University of Technology’s airborne wind energy research group established by the former astronaut Wubbo Ockels. The company is located in Delft, Netherlands, and currently comprises 18 employees (2018).

References

  1. Roberts, Bryan R.; Shepard, David H.; Caldeira, Ken; Cannon, M. Elizabeth; Eccles, Da G.; Grenier, Albert J.; Freidin, Jonathan F. (2007). "Harnessing High-Altitude Wind Power". IEEE Transactions on Energy Conversion. 22 (1): 136–144. Bibcode:2007ITEnC..22..136R. doi:10.1109/TEC.2006.889603. S2CID   1833299.
  2. Flight Without Fuel - Regenerative Soaring Feasibility Study
  3. 1 2 Wind Turbines on Mounts
  4. SkySails Archived 2010-01-05 at the Wayback Machine
  5. Anne Quéméré, the Oceankite and Extreme Weather
  6. Wind Power Curves Archived 2008-12-09 at the Wayback Machine
  7. The Power of the Wind: Cube of Wind Speed by the Danish Wind Industry Association Archived 2009-10-31 at the Wayback Machine
  8. Global Assessment of High-Altitude Wind Power
  9. High Altitude Wind Resource Modeling & Analyses, Archan Padmanabhan
  10. Windswept and Interested ltd via rotary kite sets exploiting Tensile Rotary Power Transfer.
  11. Makani Power, Inc. reported that they have progress on a tethered circling turbine glider-like craft that is powered at times and unpowered at times during energy generation. Report was at HAWP 2009 conference at Cleanteach Innovation Center in November 2009.
  12. Piezoelectric materials
  13. Joby Energy Archived 2017-04-20 at the Wayback Machine
  14. KiteShip - Innovation in Tethered Flight Archived 2010-03-05 at the Wayback Machine
  15. 1 2 John Gay's Work for Boys. Four volumes. The summer volume had Chapter XVIII titled Kite-Ship that well described HAWP kite-tugging dynamics.
  16. Mechanics of classical kite buggying or how Mr. Pocock gained 9 m/s by his Charvolant Archived 2011-08-10 at the Wayback Machine
  17. SwissKitePower; designer of KCU was Corey Houle.
  18. KiteGen project control as key technology for a quantum leap in wind energy generators by M. Canale, L. Fagiano, M. Milanese, and M. Ippolito.
  19. "Airborne Wind Turbines – A Technical Report". Scope e-Knowledge Center Pvt Ltd. 2013. Archived from the original on 2015-09-24.
  20. "KiteGen: Investment rounds, top customers, partners and investors | i3 Connect". i3connect.com. Retrieved 2018-09-10.
  21. TWIND Archived 2009-12-16 at the Wayback Machine
  22. Magenn Power, Inc. Archived 2008-12-11 at the Wayback Machine
  23. LTA Windpower
  24. Funneled-Wind Turbine Aircraft Application for patent Patent application: Pub. No.: US 2008/0290665 A1, Publication date:November 27, 2008. Inventor: Lynn Potter of Barstow, California (US). [ permanent dead link ]
  25. Airship power turbine, US Patent 4166596 by William J. Mouton, Jr., and David F. Thompson, filed April 28, 1978.
  26. "HAWE system Omnidea". Archived from the original on 2015-02-26. Retrieved 2015-02-26.
  27. "LinkedIn Post by Garrett Smith" . Retrieved 2022-11-11.
  28. Michailidis, Giannis (2023-01-09), High-Altitude-Wind-Turbine-Concept , retrieved 2023-02-22
  29. Bahrain World Trade Center examples a completed bridge holding wind turbines high above the ground; as the turbines are not tethered into the wind, this examples a twin-tower non-tethered non-airborne arrangement.
  30. Pocock’s ‘The Aeropleustic Art’ Archived 2011-07-23 at the Wayback Machine
  31. Ramsdal, Roald (22 September 2017). "Vil lokke internasjonale konkurrenter til nytt norsk testsenter for flyvende vindkraft". Teknisk Ukeblad . Retrieved 23 September 2017.
  32. The Aeropleustic Art Archived 2006-12-09 at the Wayback Machine
  33. The paradise within the reach of all men, without labor. Volumes 1-2 By John Adolphus Etzler. "We might extend the application of [wind] power to the heights of the clouds, by means of kites."
  34. US Patent 2368630 filed June 3, 1943.
  35. "M.E.A. - Mankind's Future".
  36. Tapping High Altitude Wind, 'Ladder' of Kites Viewed as Energy Source Archived 2006-07-15 at the Wayback Machine
  37. Selsam Innovations
  38. BBC News, SciTech.
  39. J. Energy, 1980, vol. 4., no. 3.
  40. Robert's Rotorcraft photograph of experiment in Australia. PJ Shepard places year at 1986 at best memory. Bryan Roberts recalls the photograph was at his session in May 1986. In the photograph the powered craft was almost in autorotation; actual electricity generation was done briefly in another test. A video is available where electric generation was effected. The shown craft had two rotating hubs; at each hub radiated a lifting rotor blade and a shorter streamlined blade with a counter-balancing mass at its tip Professor plans flying power station; total craft weighed 64 lb. From left to right the people: Hasso Nibbe, Alan Fien, Grahame Levitt, and Bryan Roberts; all were employees of the University of Sydney. Site: Mt. Pleasant Farm at Marulan in New South Wales. Wind: approximately 15 knots. AWECS inventor David H. Shepard after much correspondence finally met face-to-face in 2006 Professor Bryan Roberts; such are part of the foundations of HAWPA company Sky WindPower.
  41. Energykitesystems

Bibliography