History of wind power

Charles Brush's windmill of 1888, used for generating electricity.

Wind power has been used as long as humans have put sails into the wind. For more than two millennia wind-powered machines have ground grain and pumped water. 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 mid-west or the Australian outback, wind pumps provided water for livestock and steam engines.

With the development of electric power, wind power found new applications in lighting buildings remote from centrally-generated power. Throughout the 20th century parallel paths developed small wind plants suitable for farms or residences, and larger utility-scale wind generators that could be connected to electricity grids for remote use of power. Today wind powered generators operate in every size range between tiny plants for battery charging at isolated residences, up to near-gigawatt sized offshore wind farms that provide electricity to national electrical networks.

By 2014, over 240,000 commercial-sized wind turbines were operating in the world, producing 4% of the world's electricity.[1][2]

Antiquity

Heron's wind-powered organ, the earliest machine powered by a windwheel[3]

Sailboats and sailing ships have been using wind power for at least 5,500 years, and architects have used wind-driven natural ventilation in buildings since similarly ancient times. The use of wind to provide mechanical power came somewhat later in antiquity.

The Babylonian emperor Hammurabi planned to use wind power for his ambitious irrigation project in the 17th century BC.[4]

The windwheel of the engineer Heron of Alexandria in 1st-century AD Roman Egypt is the earliest known instance of using a wind-driven wheel to power a machine.[3][5] Another early example of a wind-driven wheel was the prayer wheel, which has been used in ancient India, Tibet, and China since the 4th century.[6]

Early Middle Ages

The Persian, horizontal windmill
Medieval depiction of a windmill

The first practical windmills were in use in Sistan, a region in Iran and bordering Afghanistan, at least by the 9th century and possibly as early as the 7th century. These "Panemone windmills" were horizontal windmills,[note 1] which had long vertical driveshafts with six to twelve rectangular sails covered in reed matting or cloth.[7] These windmills were used to pump water, and in the gristmilling and sugarcane industries.[8] The use of windmills became widespread across the Middle East and Central Asia, and later spread to China and India.[9] Vertical windmills were later used extensively in Northwestern Europe to grind flour beginning in the 1180s, and many examples still exist.[10] By 1000 AD, windmills were used to pump seawater for salt-making in China and Sicily.[11]

Wind-powered automata are known from the mid-8th century: wind-powered statues that "turned with the wind over the domes of the four gates and the palace complex of the Round City of Baghdad". The "Green Dome of the palace was surmounted by the statue of a horseman carrying a lance that was believed to point toward the enemy. This public spectacle of wind-powered statues had its private counterpart in the 'Abbasid palaces where automata of various types were predominantly displayed."[12]

Late Middle Ages

The vertical windmills of Campo de Criptana were immortalized in chapter VIII of Don Quixote.

The first windmills in Europe appear in sources dating to the twelfth century. These early European windmills were sunk post mills. The earliest certain reference to a windmill dates from 1185, in Weedley, Yorkshire, although a number of earlier but less certainly dated twelfth-century European sources referring to windmills have also been adduced.[13] While it is sometimes argued that crusaders may have been inspired by windmills in the Middle East, this is unlikely since the European vertical windmills were of significantly different design than the horizontal windmills of Afghanistan. Lynn White Jr., a specialist in medieval European technology, asserts that the European windmill was an "independent invention;" he argues that it is unlikely that the Afghanistan-style horizontal windmill had spread as far west as the Levant during the Crusader period.[14] In medieval England rights to waterpower sites were often confined to nobility and clergy, so wind power was an important resource to a new middle class.[15] In addition, windmills, unlike water mills, were not rendered inoperable by the freezing of water in the winter.

By the 14th century Dutch windmills were in use to drain areas of the Rhine River delta.

18th century

Windmills were used to pump water for salt making on the island of Bermuda, and on Cape Cod during the American revolution.[11] In Mykonos and in other islands of Greece windmills were used to mill flour and remained in use until the early 20th century.[16] Many of them are now refurbished to be inhabited.[17]

19th century

Blyth's windmill at his cottage in Marykirk in 1891
Wind powered generators were used on ships by the end of the 19th century, as seen on the New Zealand sailing ship "Chance" (1902).

The first wind turbine used for the production of electricity was built in Scotland in July 1887 by Prof James Blyth of Anderson's College, Glasgow (the precursor of Strathclyde University).[18] Blyth's 10 m high, cloth-sailed wind turbine was installed in the garden of his holiday cottage at Marykirk in Kincardineshire and was used to charge accumulators developed by the Frenchman Camille Alphonse Faure, to power the lighting in the cottage,[18] thus making it the first house in the world to have its electricity supplied by wind power.[19] Blyth offered the surplus electricity to the people of Marykirk for lighting the main street, however, they turned down the offer as they thought electricity was "the work of the devil."[18] Although he later built a wind turbine to supply emergency power to the local Lunatic Asylum, Infirmary and Dispensary of Montrose, the invention never really caught on as the technology was not considered to be economically viable.[18]

Across the Atlantic, in Cleveland, Ohio a larger and heavily engineered machine was designed and constructed in the winter of 1887-1888 by Charles F. Brush,[20] this was built by his engineering company at his home and operated from 1886 until 1900.[21] The Brush wind turbine had a rotor 17 m (56 foot) in diameter and was mounted on an 18 m (60 foot) tower. Although large by today's standards, the machine was only rated at 12 kW; it turned relatively slowly since it had 144 blades. The connected dynamo was used either to charge a bank of batteries or to operate up to 100 incandescent light bulbs, three arc lamps, and various motors in Brush's laboratory. The machine fell into disuse after 1900 when electricity became available from Cleveland's central stations, and was abandoned in 1908.[22]

In 1891 Danish scientist, Poul la Cour, constructed a wind turbine to generate electricity, which was used to produce hydrogen[18] by electrolysis to be stored for use in experiments and to light the Askov High school. He later solved the problem of producing a steady supply of power by inventing a regulator, the Kratostate, and in 1895 converted his windmill into a prototype electrical power plant that was used to light the village of Askov.[23]

In Denmark there were about 2,500 windmills by 1900, used for mechanical loads such as pumps and mills, producing an estimated combined peak power of about 30 MW.

In the American midwest between 1850 and 1900, a large number of small windmills, perhaps six million, were installed on farms to operate irrigation pumps.[24] Firms such as Star, Eclipse, Fairbanks-Morse, and Aeromotor became famed suppliers in North and South America.

20th century

Development in the 20th century might be usefully divided into the periods:

  • 1900–1973, when widespread use of individual wind generators competed against fossil fuel plants and centrally-generated electricity
  • 1973–onward, when the oil price crisis spurred investigation of non-petroleum energy sources.

1900–1973

Danish development

In Denmark wind power was an important part of a decentralized electrification in the first quarter of the 20th century, partly because of Poul la Cour from his first practical development in 1891 at Askov. By 1908 there were 72 wind-driven electric generators from 5 kW to 25 kW. The largest machines were on 24 m (79 ft) towers with four-bladed 23 m (75 ft) diameter rotors.[25] In 1957 Johannes Juul installed a 24 m diameter wind turbine at Gedser, which ran from 1957 until 1967. This was a three-bladed, horizontal-axis, upwind, stall-regulated turbine similar to those now used for commercial wind power development.[25]

Farm power and isolated plants

In 1927 the brothers Joe Jacobs and Marcellus Jacobs opened a factory, Jacobs Wind in Minneapolis to produce wind turbine generators for farm use. These would typically be used for lighting or battery charging, on farms out of reach of central-station electricity and distribution lines. In 30 years the firm produced about 30,000 small wind turbines, some of which ran for many years in remote locations in Africa and on the Richard Evelyn Byrd expedition to Antarctica.[26] Many other manufacturers produced small wind turbine sets for the same market, including companies called Wincharger, Miller Airlite, Universal Aeroelectric, Paris-Dunn, Airline and Winpower.

In 1931 the Darrieus wind turbine was invented, with its vertical axis providing a different mix of design tradeoffs from the conventional horizontal-axis wind turbine. The vertical orientation accepts wind from any direction with no need for adjustments, and the heavy generator and gearbox equipment can rest on the ground instead of atop a tower.

By the 1930s windmills were widely used to generate electricity on farms in the United States where distribution systems had not yet been installed. Used to replenish battery storage banks, these machines typically had generating capacities of a few hundred watts to several kilowatts. Beside providing farm power, they were also used for isolated applications such as electrifying bridge structures to prevent corrosion. In this period, high tensile steel was cheap, and windmills were placed atop prefabricated open steel lattice towers.

The most widely used small wind generator produced for American farms in the 1930s was a two-bladed horizontal-axis machine manufactured by the Wincharger Corporation. It had a peak output of 200 watts. Blade speed was regulated by curved air brakes near the hub that deployed at excessive rotational velocities. These machines were still being manufactured in the United States during the 1980s. In 1936, the U.S. started a rural electrification project that killed the natural market for wind-generated power, since network power distribution provided a farm with more dependable usable energy for a given amount of capital investment.

In Australia, the Dunlite Corporation built hundreds of small wind generators to provide power at isolated postal service stations and farms. These machines were manufactured from 1936 until 1970.[27]

Utility-scale turbines

The world's first megawatt-sized wind turbine near Grandpa's Knob Summit,, Castleton, Vermont.[28]
Experimental wind turbine at Nogent-le-Roi, France, 1955.

A forerunner of modern horizontal-axis utility-scale wind generators was the WIME D-30 in service in Balaklava, near Yalta, USSR from 1931 until 1942. This was a 100 kW generator on a 30 m (100 ft) tower, connected to the local 6.3 kV distribution system. It had a three-bladed 30 metre rotor on a steel lattice tower.[29] It was reported to have an annual load factor of 32 per cent,[30] not much different from current wind machines.[31]

In 1941 the world's first megawatt-size wind turbine was connected to the local electrical distribution system on the mountain known as Grandpa's Knob in Castleton, Vermont, United States. It was designed by Palmer Cosslett Putnam and manufactured by the S. Morgan Smith Company. This 1.25 MW Smith-Putnam turbine operated for 1100 hours before a blade failed at a known weak point, which had not been reinforced due to war-time material shortages. No similar-sized unit was to repeat this "bold experiment" for about forty years.[28]

Fuel-saving turbines

During the Second World War, small wind generators were used on German U-boats to recharge submarine batteries as a fuel-conserving measure. In 1946 the lighthouse and residences on the island of Neuwerk were partly powered by an 18 kW wind turbine 15 metres in diameter, to economize on diesel fuel. This installation ran for around 20 years before being replaced by a submarine cable to the mainland.[32]

The Station d'Etude de l'Energie du Vent at Nogent-le-Roi in France operated an experimental 800 KVA wind turbine from 1956 to 1966.[33]


The NASA/DOE 7.5 megawatt Mod-2 three turbine cluster in Goodnoe Hills, Washington in 1981.
Comparison of NASA wind turbines

1973–2000

US development

From 1974 through the mid-1980s the United States government worked with industry to advance the technology and enable large commercial wind turbines. The NASA wind turbines were developed under a program to create a utility-scale wind turbine industry in the U.S. With funding from the National Science Foundation and later the United States Department of Energy (DOE), a total of 13 experimental wind turbines were put into operation, in four major wind turbine designs. This research and development program pioneered many of the multi-megawatt turbine technologies in use today, including: steel tube towers, variable-speed generators, composite blade materials, partial-span pitch control, as well as aerodynamic, structural, and acoustic engineering design capabilities. The large wind turbines developed under this effort set several world records for diameter and power output. The MOD-2 wind turbine cluster of three turbines produced 7.5 megawatts of power in 1981. In 1987, the MOD-5B was the largest single wind turbine operating in the world with a rotor diameter of nearly 100 meters and a rated power of 3.2 megawatts. It demonstrated an availability of 95 percent, an unparalleled level for a new first-unit wind turbine. The MOD-5B had the first large-scale variable speed drive train and a sectioned, two-blade rotor that enabled easy transport of the blades. The 4 megawatt WTS-4 held the world record for power output for over 20 years. Although the later units were sold commercially, none of these two-bladed machines were ever put into mass production. When oil prices declined by a factor of three from 1980 through the early 1990s,[34] many turbine manufacturers, both large and small, left the business. The commercial sales of the NASA/Boeing Mod-5B, for example, came to an end in 1987 when Boeing Engineering and Construction announced they were "planning to leave the market because low oil prices are keeping windmills for electricity generation uneconomical."[35]

Later, in the 1980s, California provided tax rebates for wind power. These rebates funded the first major use of wind power for utility electricity. These machines, gathered in large wind parks such as at Altamont Pass would be considered small and un-economic by modern wind power development standards.

Danish development

A giant change took place in 1978 when the world's first multi-megawatt wind turbine was constructed. It pioneered many technologies used in modern wind turbines and allowed Vestas, Siemens and others to get the parts they needed. Especially important was the novel wing construction using help from German aeronautics specialists. The power plant was capable of delivering 2MW, had a tubular tower, pitch controlled wings and three blades. It was built by the teachers and students of the Tvind school. Before completion these "amateurs" were much ridiculed. The turbine still runs today and looks almost identical to the newest most modern mills.

Danish commercial wind power development stressed incremental improvements in capacity and efficiency based on extensive serial production of turbines, in contrast with development models requiring extensive steps in unit size based primarily on theoretical extrapolation. A practical consequence is that all commercial wind turbines resemble the Danish model, a light-weight three-blade upwind design.[36]

All major horizontal axis turbines today rotate the same way (clockwise) to present a coherent view. However, early turbines rotated counter-clockwise like the old windmills, but a shift occurred from 1978 and on. The individualist-minded blade supplier Økær made the decision to change direction in order to be distinguished from the collective Tvind and their small wind turbines. Some of the blade customers were companies that later evolved into Vestas, Siemens, Enercon and Nordex. Public demand required that all turbines rotate the same way, and the success of these companies made clockwise the new standard.[37]

Self-sufficiency and back-to-the-land

In the 1970s many people began to desire a self-sufficient life-style. Solar cells were too expensive for small-scale electrical generation, so some turned to windmills. At first they built ad-hoc designs using wood and automobile parts. Most people discovered that a reliable wind generator is a moderately complex engineering project, well beyond the ability of most amateurs. Some began to search for and rebuild farm wind generators from the 1930s, of which Jacobs Wind Electric Company machines were especially sought after. Hundreds of Jacobs machines were reconditioned and sold during the 1970s.

Following experience with reconditioned 1930s wind turbines, a new generation of American manufacturers started building and selling small wind turbines not only for battery-charging but also for interconnection to electricity networks. An early example would be Enertech Corporation of Norwich, Vermont, which began building 1.8 kW models in the early 1980s.

In the 1990s, as aesthetics and durability became more important, turbines were placed atop tubular steel or reinforced concrete towers. Small generators are connected to the tower on the ground, then the tower is raised into position. Larger generators are hoisted into position atop the tower and there is a ladder or staircase inside the tower to allow technicians to reach and maintain the generator, while protected from the weather.

21st century

Size comparison of modern wind turbines

As the 21st century began, fossil fuel was still relatively cheap, but rising concerns over energy security, global warming, and eventual fossil fuel depletion led to an expansion of interest in all available forms of renewable energy. The fledgling commercial wind power industry began expanding at a robust growth rate of about 25% per year, driven by the ready availability of large wind resources, and falling costs due to improved technology and wind farm management.[38]

The steady run-up in oil prices after 2003 led to increasing fears that peak oil was imminent, further increasing interest in commercial wind power. Even though wind power generates electricity rather than liquid fuels, and thus is not an immediate substitute for petroleum in most applications (especially transport), fears over petroleum shortages only added to the urgency to expand wind power. Earlier oil crises had already caused many utility and industrial users of petroleum to shift to coal or natural gas. Wind power showed potential for replacing natural gas in electricity generation on a cost basis.

Technological innovations, enabled by advances in computer aided engineering,[39] continue to drive new developments in the application of wind power.[40][41] By 2015, the largest wind turbine were 8MW capacity Vestas V164 for offshore use. By 2014, over 240,000 commercial-sized wind turbines were operating in the world, producing 4% of the world's electricity.[1][2] Total installed capacity exceeded 336GW in 2014 with China, the U.S., Germany, Spain and Italy leading in installations.

Floating wind turbine technology

Offshore wind power began to expand beyond fixed-bottom, shallow-water turbines beginning late in the first decade of the 2000s. The world's first operational deep-water large-capacity floating wind turbine, Hywind, became operational in the North Sea off Norway in late 2009[42] [43] at a cost of some 400 million kroner (around US$62 million) to build and deploy.[44]

These floating turbines are a very different construction technology—closer to floating oil rigs rather—than traditional fixed-bottom, shallow-water monopile foundations that are used in the other large offshore wind farms to date.

By late 2011, Japan announced plans to build a multiple-unit floating wind farm, with six 2-megawatt turbines, off the Fukushima coast of northeast Japan where the 2011 tsunami and nuclear disaster has created a scarcity of electric power.[45] After the evaluation phase is complete in 2016, "Japan plans to build as many as 80 floating wind turbines off Fukushima by 2020"[45] at a cost of some 10-20 billion Yen.[46]

Airborne turbines

Airborne wind energy systems use airfoils or turbines supported in the air by buoyancy or by aerodynamic lift. The purpose is to eliminate the expense of tower construction, and allow extraction of wind energy from steadier, faster, winds higher in the atmosphere. As yet no grid-scale plants have been constructed. Many design concepts have been demonstrated.[47][48][49]

See also

Notes

  1. ^ The terms "horizontal" and "vertical" refer to the plane of rotation of the sails. Modern wind turbines are generally referred to by the plane of rotation of the main axle (windshaft). Thus a horizontal mill may also be described as a "vertical-axis windmill" and a vertical mill may also be described as a "horizontal-axis windmill".

References

  1. 1 2 Wind in numbers, Global Wind Energy Council
  2. 1 2 The World Wind Energy Association (2014). 2014 Half-year Report. WWEA. pp. 1–8.
  3. 1 2 Dietrich Lohrmann, "Von der östlichen zur westlichen Windmühle", Archiv für Kulturgeschichte, Vol. 77, Issue 1 (1995), pp.1-30 (10f.)
  4. ↑ Sathyajith, Mathew (2006). Wind Energy: Fundamentals, Resource Analysis and Economics. Springer Berlin Heidelberg. pp. 1–9. ISBN 978-3-540-30905-5.
  5. ↑ A.G. Drachmann, "Heron's Windmill", Centaurus, 7 (1961), pp. 145-151
  6. ↑ Lucas, Adam (2006). Wind, Water, Work: Ancient and Medieval Milling Technology. Brill Publishers. p. 105. ISBN 90-04-14649-0.
  7. ↑ Ahmad Y Hassan, Donald Routledge Hill (1986). Islamic Technology: An illustrated history, p. 54. Cambridge University Press. ISBN 0-521-42239-6.
  8. ↑ Lucas, Adam (2006). Wind, Water, Work: Ancient and Medieval Milling Technology. Brill Publishers. p. 65. ISBN 90-04-14649-0.
  9. ↑ Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, p. 64-69. (cf. Donald Routledge Hill, Mechanical Engineering Archived 25 December 2007 at the Wayback Machine.)
  10. ↑ Dietrich Lohrmann, "Von der östlichen zur westlichen Windmühle", Archiv für Kulturgeschichte, Vol. 77, Issue 1 (1995), pp.1-30 (18ff.)
  11. 1 2 Mark Kurlansky, Salt: a world history,Penguin Books, London 2002 ISBN 0-14-200161-9, pg. 419
  12. ↑ Meri, Josef W. (2005). Medieval Islamic Civilization: An Encyclopedia. 2. Routledge. p. 711. ISBN 0-415-96690-6.
  13. ↑ Lynn White Jr., Medieval technology and social change (Oxford, 1962) p. 87.
  14. ↑ Lynn White Jr. Medieval technology and social change (Oxford, 1962) p. 86-87, 161-162.
  15. ↑ History of Wind Energy in Energy Encyclopedia Vol. 6, page 420
  16. ↑ Administrator. "Μύκονος Ανεμόμυλοι". mymykonos.eu. Retrieved 8 February 2016.
  17. ↑ "Ανεμόμυλοι Μυκόνου". mykonos-tours.gr. Retrieved 8 February 2016.
  18. 1 2 3 4 5 Price, Trevor J (3 May 2005). "James Blyth - Britain's First Modern Wind Power Engineer". Wind Engineering. 29 (3): 191–200. doi:10.1260/030952405774354921.
  19. ↑ Shackleton, Jonathan. "World First for Scotland Gives Engineering Student a History Lesson". The Robert Gordon University. Archived from the original on 17 December 2008. Retrieved 20 November 2008.
  20. ↑ [Anon, 1890, 'Mr. Brush's Windmill Dynamo', Scientific American, vol 63 no. 25, 20 December, p. 54]
  21. ↑ A Wind Energy Pioneer: Charles F. Brush Archived 8 September 2008 at the Wayback Machine., Danish Wind Industry Association. Accessed 2 May 2007.
  22. ↑ History of Wind Energy in Cutler J. Cleveland,(ed) Encyclopedia of Energy Vol.6, Elsevier, ISBN 978-1-60119-433-6, 2007, pp. 421-422
  23. ↑ Warnes, Kathy. "Poul la Cour Pioneered Wind Mill Power in Denmark". History, because it's there. Archived from the original on 29 January 2013. Retrieved 20 January 2013.
  24. ↑ History of Wind Energy in Encyclopedia of Energy,pg. 421
  25. 1 2 History of Wind Energy in Encyclopedia of Energy Vol. 6, page 426
  26. ↑ History of Wind Energy in Energy Encyclopedia vol. 6, page 422
  27. ↑ http://www.pearen.ca/dunlite/Dunlite.htm Dunlite history page Retrieved 28 November 2009
  28. 1 2 The Return of Windpower to Grandpa's Knob and Rutland County Archived 28 August 2008 at the Wayback Machine., Noble Environmental Power, LLC, 12 November 2007. Retrieved from Noblepower.com website 10 January 2010. Comment: this is the real name for the mountain the turbine was built, in case you wondered.
  29. ↑ Erich Hau, Wind turbines: fundamentals, technologies, application, economics, Birkhäuser, 2006 ISBN 3-540-24240-6, page 32, with a photo
  30. ↑ Alan Wyatt, Electric Power: Challenges and Choices,(1986),Book Press Ltd., Toronto, ISBN 0-920650-00-7 , page NN
  31. ↑ See also Robert W. Righter Wind energy in America: a history page 127 which gives a slightly different description.
  32. ↑ Dimitri R. Stein, Pioneer in the North Sea: 1946 Insel Neuwerk Turbine, in IEEE Power and Energy Magazine, September/October 2009, pp. 62-68
  33. ↑ Cavey, Jean-Luc (2004). "The 800 KVA BEST - Romani Aerogenerator". Retrieved 26 November 2008.
  34. ↑ Price of petroleum,
  35. ↑ http://www.seattlepi.com/archives/1987/8701230009.asp%5Bpermanent+dead+link%5D Hawaiians get Boeing's Last Wind Machine Makani Ho'Olapa will Bring Power to 1,140 Residences 1987
  36. ↑ Paul Gipe Wind Energy Comes of Age, John Wiley and Sons, 1995 ISBN 0-471-10924-X, Chapter 3
  37. ↑ Grove-Nielsen, Erik. Økær Vind Energi 1977 - 1981 Winds of Change. Retrieved: 1 May 2010.
  38. ↑ "BTM Forecasts 340-GW of Wind Energy by 2013". Renewableenergyworld.com. 27 March 2009. Retrieved 29 August 2010.
  39. ↑ Hewitt, Sam; Margetts, Lee & Revell, Alistair (18 April 2017). "Building a digital wind farm". Archives of Computational Methods in Engineering. Retrieved 20 April 2017.
  40. ↑ Clive, P. J. M., Windpower 2.0: technology rises to the challenge Environmental Research Web, 2008. Retrieved: 9 May 2014.
  41. ↑ Clive, P. J. M., The emergence of eolics, TEDx University of Strathclyde (2014). Retrieved 9 May 2014.
  42. ↑ Madslien, Jorn (8 September 2009). "Floating challenge for offshore wind turbine". BBC News. Retrieved 14 September 2009.
  43. ↑ Ramsey Cox (February–March 2010). "Water Power + Wind Power = Win!". Mother Earth News. Retrieved 3 May 2010.
  44. ↑ "Statoil Draws On Offshore Oil Expertise To Develop World's First Floating Wind Turbine". NewTechnology magazine. 8 September 2009. Retrieved 21 October 2009.
  45. 1 2 "Japan Plans Floating Wind Power Plant". Breakbulk. 16 September 2011. Archived from the original on 21 May 2012. Retrieved 12 October 2011.
  46. ↑ Yoko Kubota Japan plans floating wind power for Fukushima coast Reuters, 13 September 2011. Accessed: 19 September 2011.
  47. ↑ Griffith, Saul. "High-altitude wind energy from kites! (video)". Retrieved 5 March 2014.
  48. ↑ Goldstein, Leo. "Why Airborne Wind Energy". Archived from the original on 11 August 2014. Retrieved 5 March 2014.
  49. ↑ Energy Kite Systems http://www.energykitesystems.net
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