Exploring the Potential of High Altitude Wind Energy

And despite a host of tech­ni­cal and reg­u­la­tory chal­lenges, a grow­ing num­ber of small com­pa­nies are work­ing hard to get up there within the next few years, with numer­ous designs and ideas aimed at har­vest­ing wind power high in the sky.

“The poten­tial is incred­i­bly high,” says Cristina Archer, an asso­ciate pro­fes­sor of ocean sci­ence and engi­neer­ing at the University of Delaware. Archer and a col­league pub­lished one of two recent detailed analy­ses of the total energy that could be extracted from the planet’s winds to gen­er­ate elec­tric­ity. The other was con­ducted by well-known cli­mate sci­en­tist Ken Caldeira of the Carnegie Institution and Stanford University. Both found an effec­tively unlim­ited sup­ply of power, with vastly more avail­able as one moves up away from the ground.

But Caldeira and oth­ers say that while they see enor­mous long-term poten­tial in air­borne wind, the engi­neer­ing and reg­u­la­tory chal­lenges are for­mi­da­ble, par­tic­u­larly if com­pa­nies want to tap into pow­er­ful jet stream winds.

“I would be reluc­tant to remort­gage my house and invest the money in these com­pa­nies, because I think the prob­a­bil­ity of them being able to com­pete in the mar­ket­place at scale in, say, the next decade is pretty small,” he says. Nevertheless, he believes that given both its enor­mous pos­si­bil­i­ties and the var­i­ous hur­dles it faces, the air­borne wind indus­try is an ideal can­di­date for pub­lic research and devel­op­ment support.

The ques­tions sur­round­ing air­borne wind are sig­nif­i­cant. How do you safely sus­pend air­borne tur­bines hun­dreds or thou­sands of feet off the ground? How do you keep them aloft for long peri­ods of time in high winds with­out hav­ing to per­form fre­quent, costly main­te­nance? And what about inter­fer­ence with aviation?

Proponents say, how­ever, that in some ways high-altitude wind power could end up being eas­ier to deploy—and cheaper—than tra­di­tional wind energy. Construction costs will be markedly dimin­ished with no need for giant steel and con­crete tow­ers, and there will be no need for the yaw mech­a­nism that keeps stan­dard tur­bines fac­ing into the wind as wind direc­tion changes.

Instead, the basic premise of air­borne gen­er­a­tion is to tether a device to the ground and let it fly around in the strong winds like a kite, either gen­er­at­ing power and send­ing it down a tether to the ground or using the tether itself to pro­duce elec­tric­ity at its base. The spe­cific devices on the end of the tether vary widely in design. Terrestrial wind­mill design is largely set­tled; but up in the sky, it seems like any­thing goes. There are rigid, carbon-fiber wings out­fit­ted with mul­ti­ple small tur­bines; softer kite-like devices that fly in figure-eights and gen­er­ate power by coil­ing and uncoil­ing a tether; devices that resem­ble a blimp rotat­ing around a hor­i­zon­tal axis; and sev­eral other con­cepts. No con­sen­sus exists on an opti­mal design, though some may be bet­ter suited for utility-scale wind farms while oth­ers may fit smaller, niche-market applications.

One com­pany that seems close to deploy­ment is Makani Power, based in Alameda, California. Makani’s teth­ered rigid wing has been through seven devel­op­ment iter­a­tions and numer­ous test flights in six years, and the lat­est pro­to­type can gen­er­ate 30 kilo­watts of power. With close to $20 mil­lion in fund­ing from Google and the Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E), Makani hopes to build a 92-foot wingspan ver­sion rated at 600 kilo­watts, which could sup­ply power to about 150 households.

Corwin Hardham, the founder and CEO of Makani, says the com­pany has inter­est from devel­op­ers and could start build­ing air­borne wind farms within a few years. Farther in the future, Hardham hopes his com­pany can build a 5-megawatt behe­moth ver­sion, with a 213-foot wingspan best suited for off­shore use.

“That’s where our approach really shines, off­shore,” Hardham says, adding that he thinks Makani could even­tu­ally pro­duce power at 6 cents per kilowatt-hour at off­shore instal­la­tions. That’s far cheaper than cur­rent off­shore wind power in Europe and would make it extremely com­pet­i­tive with power pro­duced from coal and nat­ural gas.

Another com­pany close to actual wind farm devel­op­ment is Ampyx Power, based in the Netherlands and spun out of research at Delft University. Ampyx’s PowerPlane is a glider that gen­er­ates elec­tric­ity by pulling on its tether, which is con­nected to a ground-mounted gen­er­a­tor. The PowerPlane glides around between 1,000 and 2,000 feet; the next iter­a­tion of this design should gen­er­ate 250 to 500 kilo­watts con­tin­u­ously, says founder Richard Ruiterkamp.

“We’ve been fly­ing autonomously now for about a year,” Ruiterkamp says. “Before the end of the year we will have the full cycle up and run­ning for a num­ber of hours.” The next hur­dle, he says, is to oper­ate for mul­ti­ple days con­sec­u­tively with­out human inter­ven­tion. Ampyx says it expects con­struc­tion on a wind farm to begin within sev­eral years.

Two com­pa­nies with dra­mat­i­cally dif­fer­ent ideas are California-based Magenn Power and Boston-based Altaeros. Magenn’s helium-filled, blimp-like struc­ture floats 1,000 feet up, and the entire bal­loon spins around a hor­i­zon­tal axis as the wind blows past. This tech­nol­ogy is about as bird-friendly a design as one could imag­ine, with no spin­ning blades, and has under­gone suc­cess­ful test flights.

Click here to read the rest of this arti­cle at Yale Environment 360.