One day in early October, a curiously designed drone climbs into the bright, crisp North Carolina sky. It resembles a flimsy, fragile model airplane with about a 12-foot wingspan, but it takes off like a helicopter. A tether snakes from the ground to a complicated web of cables and control lines attached to the drone. Within a few seconds, however, one of its motors begins to wobble. This makes a team of engineers from Windlift, a Durham, N.C.-based startup, pretty nervous because wobbling is very much not in its design specs.
For Mark Aull, chief science officer of Windlift, and Andy Stough, chief technology officer, this drone represents the culmination of years of research and millions in funding. The Pentagon has awarded Windlift $24 million in research and development grants to look into airborne wind energy systems, and they have a test for the Naval Research Laboratory in Kansas in November.
“You can see how much that’s spinning around,” Aull remarks as he shows me the test flight video the next day. “From where we were observing the test, everything looked fine. But then we looked at the video, and we looked at the data, and it’s like, ‘Oh, this is not acceptable.’”
Within seconds, a test pilot takes manual control and brings the drone down in a rapid, controlled descent. The flight lasted barely 30 seconds—far short of the hoped-for three to four hours.
Windlift’s founder and CEO, Rob Creighton, runs a hand through his silver hair. “We don’t want to risk hardware and not learn anything,” he says, frustration edging his voice. “But if we crash a plane, we lose a few weeks of work, a few months in some cases.”
This setback is frustrating for Creighton and his team, but it’s all part of the process in their audacious attempt to revolutionize wind energy. The goal? To generate cheap, clean electricity and—maybe—help save the world from the effects of climate change.
“We think this can go anywhere in the world,” says Creighton, “and provide power to at least half the world’s population.”
Founded in 2006, Windlift is developing autonomous tethered drones that generate electricity. The concept is elegantly simple: As the drone swoops through a loopy sideways figure eight pattern, it generates electricity by letting the air turn the rotors on its turbine propellers as it coasts from the top of one loop to the bottom of the next. As inertia carries it back up on its next pass, its motors kick in and boost it a bit to the top of a loop to start the process again. Over and over and over.
Using the wind to do work is not a new concept. Chinese and Middle Eastern miller used wood and fabric windmills as early as 200 BC to mill flour. Today, we use gusts of wind to spin 400-foot-long aluminum windmill blades, turn turbines, and create electricity, which powers, for example, factories that mill flour. Plus ça change.
But those massive windmills and their equally massive turbines use a lot of material. The largest proposed wind turbine in the world, GE’s Haliade-X, stands about 853 feet high, with a rotor diameter of 722 feet and a blade sweep surface of 410,000 square feet—about seven American football fields. It also uses approximately 825 tons of steel, fiberglass, aluminum, and reinforced polymers.
Windlift is one of about 12 companies in the world, most of them in Europe, experimenting with airborne wind energy systems. Aside from Windlift and the German firm Kitekraft, however, they’re mainly using balloons and kites rather than autonomous drones.
When he first founded Windlift, Creighton also experimented with tethered kites and inflatable wings, , but after a meeting with the Marine Corps System Command, Creighton, Stough, and Aull realized the kite and wing plan wouldn’t work for generating power in the field, one of his original plans for the company. They realized that to generate electricity, you need to get a generator into the windy areas, but you don’t need to build a massive steel tower that protrudes into the lower heavens. What if you could get the generator itself up high, like on a drone, for example? And there you have it: Wind power without the massive resource needs.
“The physics of our system are just hugely advantageous,” says Creighton.“ The massive steel towers exist to make the tip of the blade sweep through the air, accelerated by the wind. A tether replaces all that mass, attaching to a wing that sweeps an area like the tip of the blade, because that’s the most efficient part.”
Creighton says their technology could reduce material requirements by 90% compared to traditional wind turbines. Electricity generating costs could be cut by up to 80%, especially for offshore applications. A small Windlift drone can theoretically generate, on average, 30kWh, enough electricity to power a typical American home, but tether a few thousand of these swooping drones to an array of offshore buoys, connect them to existing transmission lines, and you’ve got the potential for some real savings.
It’s an enticing vision that’s been pursued before—with sobering results. From 2006 to 2020, Google’s secretive X lab poured hundreds of millions of dollars into Project Makani, a similar attempt at airborne wind energy focusing on offshore deployment. But its drone was too big and didn’t produce enough power to make it a net generator of electricity. It also didn’t help that it crashed during a major demonstration. Despite backing from one of the world’s most resourceful tech companies and later support from energy giant Shell, during a cost-cutting period Alphabet ultimately pulled funding for Makani, sealing its fate.
When it comes to wind energy, offshore is where it’s at. The winds are stronger and more consistent; vast stretches of ocean are free from pesky land-use restrictions; and—very important—it’s where the people are. Approximately half of the world’s population lives within 200km of a coast, many in cities thirsty for electricity.
The math is in Windlift’s favor. Offshore turbines rarely operate at full capacity. They ramp up to their full rated capacity only in high winds, but during lower wind conditions, they often sit idle. Windlift’s smaller drones are optimized to generate power in lower winds, using existing transmission systems without additional costly infrastructure.
Makani’s founders and Alphabet, the parent company of Google, were generous in publicly sharing their patents, data, and findings. Creighton and his team have used that data in their efforts to develop smaller, more agile drone designs and proprietary control systems they believe will prove more reliable and efficient. The company has also focused heavily on computer modeling and simulation to refine its designs before building physical prototypes. “For the propeller blade we made, we explored tens of thousands of different versions of it in software before we built one in hardware,” Creighton explains.
And then there’s the Department of Defense, which is interested in Windlift’s work, too. It sees potential in rapidly deployed portable, high-output wind power, which could be invaluable for powering remote bases.
“It’s kind of like the Wright brothers,” says Creighton. “Like, their first flight was 100 feet, and now you can catch a flight from here to Sydney, Australia…We can have energy abundance in a way that’s harmonious with nature. To me, that is exciting. So why not do it in a better way? It just makes sense.”
