The wind turbines that increasingly dot the landscape peak at around 300 feet above ground, with the massive blades spinning a bit higher. The wind, however, does not peak at 300 feet. Winds are faster and more consistent the higher one climbs, maxing out in the jet streams at five miles and above. here comes the significance of high altitude wind turbines.
Airborne wind energy would be the world’s cheapest energy source, and on a large scale, high altitude wind energy will be able to supply the needs of the world at the best overall costs, using secured wind energy capture-devices that soar at these altitudes where wind power is much greater than it is at ground level. High-energy winds are at altitudes high above us, not just a few hundred feet where they can be captured by tower-based turbine rotors.
This is a challenge for most forms of renewable energy, but most of our renewable energy comes from wind, which is among the most unpredictable. The behavior of wind near the ground, where turbines spin, is highly variable. But a few miles up winds are strong and steady, ideal for power generation. All we have to do is tap into them.
Conventional wind turbines can’t reach the necessary altitudes. There are some plans to lift a wind turbine to that height using balloons, but perhaps the best approach is to use a kite. Or a pair of kites, to be precise.
Kite Power Systems is a U.K. company developing a new way to draw power from the wind using specially-designed kites that fly in pairs hundreds of feet above the ground, taking turns extending and retracting. Their motion powers a generator on the ground, which can produce kilowatts to megawatts of power, depending on the size of the kites, as Real Engineering explains.
With conventional wind power facing a litany of obstacles — intermittency, space requirements, not-in-my-backyard complaints — pushing wind power up into the atmosphere could take a lot of uncertainty out of the equation. 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 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.
Now Hardham, a Stanford-trained engineer, has teamed up with former professional windsurfer and kiteboarder Don Montague to take his passion for the wind and kites into the green-energy realm. Their company, Makani Power, has developed an airborne wind turbine—in effect, an enormous, tricked-out kite—that will be able to harness the greater energy potential from winds at altitudes higher than those exploited by conventional wind turbines.
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.
Other designs of high altitude wind turbines
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.
Altaeros, meanwhile, also uses a helium-filled device, though to quite different effect. The balloon shell surrounds the blades and hub of a standard turbine in the center, basically serving to lift a normal windmill 1,000 feet off the ground. The company says it successfully tested a prototype earlier this year, and reports that the turbine generated twice the power at 350 feet as the same turbine did at standard heights of about 100 feet.