technology & engineering wind power is looking up — to the

Technology & Engineering

Wind power is looking up — to the cloudsResearchers look to the skies in their search for airborne wind power

By Sid Perkins 8:00am, November 20, 2014

This special helium-filled blimp lets a wind turbine soar. Placing wind turbines high in the sky, where winds arestronger and steadier, could let them harness more energy than on the ground. VIDEO: Click here to seethe turbine in action

Altaeros Energies

For the year ending this past April, slightly more than 4 percent of U.S. electricitycame from wind power. That may not sound like much, but it’s more than 20 timesas much energy from wind as the nation produced in 2000. Wind power isbooming, largely due to a search for energy from sources other than fossil fuels,such as petroleum and coal.

Much of today’s wind power comes from big “farms” that have many tall, modern

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Wind farms filled with earthbound turbines canbe noisy, unsightly and pose threats to bats andmigrating birds. Replacing them with airbornewind turbines would address many of thoseconcerns.Luis Alves/Flickr (CC BY 2.0)

Thousands of birds in the United States are killedevery year by wind turbines. Credit: Gidzy/Flickr(CC BY 2.0)

windmills, called wind turbines. These machines have long shafts. In somedesigns, they can reach taller than a 10-story building. These shafts are topped bygiant blades. These connect to a generator that converts the energy of theirspinning motion into electricity.

But some people — even those very concerned about the effects of fossil fuels onthe environment — have growing concerns about wind power. The turbine farmsare taking up a growing fraction of the landscape. Plus, to tap the speedier windsfound at higher altitudes, the blades have been growing longer and sitting atopever-higher shafts. Together, critics say, these trends pose increasing threats towildlife.

Turbine blades strike and kill flying animalseach year, including bats and migratingbirds. For instance, an estimated 214,000 to368,000 small perching birds, many of themsongbirds, may be killed by turbine bladeseach year. That’s the conclusion of a studypublished September 15 in PLOS ONE. Thatmight sound like a lot of birds. But about 5billion of those types of birds live or breed inNorth America. This means that the fractionkilled by wind turbines is really tiny. It alsopales in comparison to the nearly 7 millionbirds that are estimated to die each yearafter flying into other tall structures, such asradio towers and cell-phone towers, thestudy’s authors point out.

Other critics think that the forests of turbines are just plain ugly. And many peoplewho live near wind farms complain about the whooshing noise made by therapidly whirling blades.

Some engineers are now investigating a seemingly radical solution — one thatmight solve many of these problems. They’d like to take the earthbound windturbines and fly them far above the ground. They could be held in place by kitesor helium-filled blimps and connected to the ground by long tethers. High above— and possibly out of the flight paths of some birds and bats — they would belargely out of sight and too high for their noise to bother anyone.

Placed in the path of steady and speedywinds, such airborne turbines could generatehuge amounts of power, analyses nowsuggest. And doing so might not cost anymore than operating wind turbines on the ground. But first, researchers will need


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In the future, fleets of airborne devices such asthis tethered turbine could harness the energy ofhigh-altitude winds to generate electrical power.Makani/Kathy F. Atkinson

to figure out how to tap into that sky-high energy and bring is safely to theground.

The air up there

Largely because of friction with Earth’s surface, winds tend to be slower at groundlevel than at high altitudes. That’s why engineers are building taller and tallerwind turbines: The higher the blades reach, the more wind they can harvest forpower.

Some of the strongest, steadiest winds on Earth are found in jet streams. Thesefast-flowing currents of air blow, for the most part, from west to east. They can befound in the mid-latitude regions of the Northern and Southern Hemispheres.

When scientists first came up with the idea of airborne wind power, someconsidered tapping into jet streams, says Cristina Archer. She’s a civil andenvironmental engineer at the University of Delaware in Newark. But to reachhigh-altitude jet streams, the tethers connecting the turbines to the ground wouldneed to be several kilometers long. Not only would these cables be heavy, butalso would pose safety hazards to aircraft carrying people, Archer notes.

So now, engineers are designing and testing wind-energy systems to fly at muchlower altitudes. In U.S. airspace, these turbines would be lofted no higher than600 meters (1,970 feet) off of the ground. Over international waters, where rulescan be less strict, a somewhat higher flying altitude might be permitted, Archersays. But even at these relatively low altitudes, winds should be far stronger thanthey are at ground level. Moreover, winds well above Earth’s surface should besteadier and less turbulent.

Airborne wind turbines might have otheradvantages, too. They could be made usinglighter, less expensive materials thanground-based turbines. And eliminating thatconventional wind turbine’s shaft and itsstrong foundation could cut costs even more. These savings might balance out thecost of putting turbines up in the clouds.

Recently, Archer and her teammates analyzed 21 years’ worth of weather datacollected worldwide to find out where airborne wind energy might be practical ataltitudes below 3 kilometers (about 9,800 feet). Winds are typically strongest insummer months. So they looked at weather data from January and July. Those arethe peak summer months in the Southern and Northern Hemispheres,respectively.

The researchers found several regions where summer winds were suitable. They


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Altaeros Energies’ system places a wind turbineinside a tube-shaped helium-filled blimp.Altaeros Energies

exceeded 36 kilometers per hour (about 22 miles per hour) at least 15 percent ofthe time. In some of those areas, the winds are far stronger at altitude than theyare near ground level. If airborne wind turbines operated in all of those regions,Archer’s team concluded, they could make about three times more electricity thanwas consumed worldwide from all sources in 2012. The researchers reported theirfindings in the April issue of Renewable Energy.

But harnessing airborne wind energy in some of those places likely would not bepractical, Archer admits. One area, for example, is off the shores of Somalia, anation in eastern Africa. Others are near Greenland and the coast of Antarctica.Even if winds in these places are strong, she notes, they are extremely remoteand any power generated there couldn’t be easily transported to a large,continental power grid. It could only be used locally.

The U.S. Great Plains, however, offers one ofthe most promising sites for airborne windpower. This area lies west of the MississippiRiver and east of the Rocky Mountains. Itstretches from Texas to the Canadian border.Here, there not only is the potential forharvesting lots of energy, but also largepopulation centers to use it and a power gridto distribute it.

Many ways to tap wind power

Many places have plenty of wind availablefor harnessing that is just a few hundredmeters up in the sky. The challenge lies indesigning devices that can tap into thatenergy efficiently and reliably.

Fortunately, there are only four mainingredients needed for an airborne windturbine, explains Christof Beaupoil. He worksat a software company he co-founded morethan a decade ago, but he trained as amechanical engineer. (That’s an engineerwho designs, builds or operates machines ormechanical systems.) Beaupoil has beeninterested in airborne wind energy for more than 20 years.

Last year, he spoke at a conference about the many different ways that engineersmight design airborne wind turbines. Two types of components would remain


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Artist’s rendition of one concept being floated forairborne wind power. This one would be basedoffshore. It involves one or two wings sailing highabove a floating base.AweCrosswind/Wikimedia Commons (CC BY-SA3.0)

similar to those in land-based turbines: the blades needed to intercept the windand the generator used to convert the energy from those rotating blades intoelectrical power.

Two other components would be unique to airborne wind-power systems. One is away to loft and hold the turbine at heights where the strong winds blow. The otheris a way to transport electricity from the turbine to the ground, where it could beused directly or sent into the electric power grid.

Combining these four ingredients to efficiently extract energy from thehigh-altitude winds is the trick, says Beaupoil. “Fortunately, there are literally amillion ways to do this.”

For instance, the blade-carrying portion of the turbine could be lifted by a kite or ahelium-filled blimp. Or the turbine could hang from a helicopter-like platform or aglider-like vehicle with a solid fixed wing. Some turbines might be designed toalways hover in the same spot, with the wind blowing past. Others might flythrough the air in a circular or figure-8 path.

The system’s electrical generator could be built into the flying device or sit on theground, near to where the tether anchors the turbine to the ground. There areadvantages and disadvantages to each option, says Beaupoil. If the generator isairborne, that makes the turbine heavier and possibly more difficult to keep aloft.The tether in these systems also must conduct live electricity to the ground. Thatmeans the tether must be insulated to make it safe. If the generator insteadremains on the ground, the wind energy has to be transferred mechanically to itvia a series of belts, pulleys or rotating shafts. That could make the tether’sdesign quite challenging.

Finally, the entire power system would needto be designed so that computers couldautomatically adjust the altitude at which theturbines fly to catch the strongest winds. Theturbines also would need to come back toEarth during bad weather or formaintenance, Beaupoil notes.

But the biggest challenges might be legalones, Archer says.

Government agencies would have to approvecloud-based turbines. Right now, rules forairborne things other than conventionalaircraft vary from country to country. In theUnited States, Archer notes, rules are


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somewhat strict about where and at what altitude something such as airbornewind turbines might be allowed. Some rules are imposed by local or stategovernments, but many are imposed by the Federal Aviation Administration.That’s the U.S. agency that regulates the nation’s airspace to keep it safe, amongother duties. “I wonder if the FAA will ever allow turbines to fly at altitudes above500 feet [about 150 meters],” Archer says.

Until such issues are resolved, airborne wind turbines might be grounded, at leastin the United States. But if the government can draft rules that allow flying windturbines, the amount of energy harvested from the wind might really soar.

Power words

blimp An airship that doesn’t have an internal framework or a keel. Mostblimps, such as those often seen over sports stadiums, gain their lift by beingfilled with helium.

civil engineer An engineer who creates buildings, tunnels, water systems andother large projects that improve everyday life.

electricity A flow of charge, usually from the movement of negatively chargedparticles, called electrons.

engineer A person who uses science to solve problems. As a verb, to engineermeans to design a device, material or process that will solve some problem orunmet need.

fixed wing The term for a type of aircraft whose wings generate lift withouthaving to move. Most jets and passenger planes fall into this category.

fossil fuels Any fuel — such as coal, petroleum (crude oil) or natural gas — thathas developed in the Earth over millions of years from the decayed remains ofbacteria, plant or animals.

generator A device used to convert mechanical energy into electrical energy.

helium An inert gas that is the lightest member of the noble gas series. Heliumcan become a solid at -458 degrees Fahrenheit (-272 degrees Celsius).

jet stream A fast-flowing, high-altitude air current. On Earth, the major jetstreams flow from west to east in the mid-latitude regions of the Northern andSouthern Hemispheres.

kinetic energy The energy held by an object due to its being in motion. Theamount of this energy contained will depend on both the mass (usually weight) ofthe object and its speed.


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mechanical engineer Someone who uses physics and materials science todesign, develop, build and test mechanical devices, including tools, engines andmachines.

mid-latitudes That part of the globe that lies midway between Earth’s tropicaland polar regions. Most people live in these temperate regions and most of theworld’s food is produced here.

power grid The interconnected system of electricity lines that transportelectrical power over long distances. In North America, this grid connectselectrical generating stations and local communities throughout most of thecontinent.

renewable energy Energy from a source that is not depleted by use, such ashydropower (water), wind power or solar power.

software The mathematical instructions that direct a computer’s hardware,including its processor, to perform certain operations.

weather Conditions in the atmosphere at a localized place and a particular time.It is usually described in terms of particular features, such as air pressure,humidity, moisture, any precipitation (rain, snow or ice), temperature and windspeed. Weather constitutes the actual conditions that occur at any time and place.It’s different from climate, which is a description of the conditions that tend tooccur in some general region during a particular month or season.

wind turbine A wind-powered device — similar to the type used to mill grain(windmills) long ago — used to generate electricity.

Word Find (click here to enlarge for printing)


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S. Zielinski. “Wind farms: Restaurants for seals?” Science News for Students. Aug.18, 2014.

S. Ornes. “’Greener’ energy needed now, group warns.” Science News forStudents. April 28, 2014.

B. Brookshire. “Teaching clean energy with the power of wind.” Eureka! Lab. April16, 2014

B. Mole. “IPCC calls for quick switch to alternative power.” Science News forStudents. April 13, 2014.

E. Sohn. “Power of the Wind.” Science News for Students. February 28, 2005.

Original Journal Article: W.P. Erickson, M.M. Wolfe, K.J. Bay, D.H. Johnson, andJ.L. Gehring. A Comprehensive Analysis of Small-Passerine Fatalities from Collisionwith Turbines at Wind Energy Facilities. PLOS ONE. Vol. 9, Sept. 15, 2014, p.

Further Reading


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Source URL: https://student.societyforscience.org/article/wind-power-looking-to-the-clouds

e107491. doi: 10.1371/journal.pone.0107491.

Original Journal Article: C.L. Archer, L.D. Monache, and D.L. Rife. Airborne windenergy: Optimal locations and variability. Renewable Energy 64 (2014):180-186.Published in April 2014. doi: 10.1016/j.renene.2013.10.044

Conference Presentation: C. Beaupoil. The Big AWE Picture. Airborne WindEnergy Conference. Beuth University, Berlin, Germany. Sept. 10-11, 2013.

Classroom questions: Wind power is looking up — to the clouds


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technology & engineering wind power is looking up — to the

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