By then Bevirt had created a second successful company, called Joby, that built gadgets like bendable tripods—dubbed Gorillapods—for outdoor photographers. But after his design for a wireless headset flopped, he decided it was time to stop wasting his efforts on small ideas and go after the sort of big dream that had captured his imagination in college. Recalling the solar panels of his childhood, he turned to renewable energy and began pursuing every hip new energy source he could find. “At one point JoeBen got all excited about algae,” his friend and former colleague David Scheinman says. “We went to algae conferences. All we talked about was algae, algae, algae. Then he kind of decided: nope.”

Algae did not have enough concentrated energy to be cost-effective, Bevirt concluded. In 2007 he was still casting about for a novel resource—one that contained so much power it would cost less than coal—when he had an epiphany in midair. “I was on a flight back from China, and the air quality over there had been just absolutely atrocious,” he says. “And I realized that we had 200-mile-an-hour tailwinds. So I started doing calculations on exactly how much power was in 200-mile-an-hour winds. By the time I landed, I was all fired up.”

Bevirt, who has always loved aviation and is an avid kite surfer, started modeling jet stream winds. Over several sleepless nights he calculated how much power a wind turbine at altitude could gather. He knew wind power is related to the cube of wind speed, so faster winds create exponentially more power than slower ones. But the actual numbers staggered him. In the jet stream above New York City, one square meter of wind routinely carries eight kilowatts of power (enough for six or seven American homes), whereas the same area near the ground could not even power a toaster oven. What’s more, high-altitude winds are more consistent, so those kilowatts would be generated virtually all the time. Produced by such constant, ferocious air currents, wind power could finally be cheaper than coal. As a bonus, elevated turbines would not mar the landscape, neutralizing one of the big political objections to wind.

“I spent several days completely focused on it, to the point where it was the only thing I could think about,” Bevirt says. He imagined a device that could fly in the relentless punishment of the jet stream: a giant wing, fitted with multiple turbines, that would take off and land like a helicopter. He created an animation of such a craft and showed it to colleagues. “Are you out of your mind?” they asked him. How would he build it or get it aloft?

Bevirt had no idea what he was getting into when he launched Joby Energy in February 2008. Sure, other companies were tinkering with high-altitude wind (see “High Fliers,” next page), but he had an advantage in his solid source of funding: his own fortune. By the end of the year, he had bought a 40-acre plot of redwood forest in the Santa Cruz Mountains to fly models around and outfitted it with workshops for metal, wood, fiberglass, and carbon fiber. He converted an old barn into a lofty research lab and bought a small house next door where he could sleep in between relentless 18-hour days.

The first thing he and his team had to decide was the type of design to pursue. Did they want something like a kite, which would generate small amounts of energy by pulling a tether and spinning a turbine on the ground? Or should they develop generators that would be affixed to a craft and sent into the sky? Bevirt was interested not in generating a few kilowatts of electricity for a single house but in making great quantities of power; for this the latter idea seemed best. He wanted a device that could be scaled to an industrial size, on par with a coal-fired plant. (Most modern wind turbines generate anywhere from 700 kilowatts to 2.5 megawatts each—enough for 200 to 750 typical homes.) Attaching turbines directly to the craft would mean more generators and therefore more power.

But what should the device look like? The team began with off-the-shelf model airplanes, attached by tether to the ground and flown in circles. This led to a bizarre early design called the Whirly, which had two rotors on opposite sides of a long wing; as the wing sliced the air, the rotors circled each other much like two animals chasing each other’s tails. The spinning generated lots of wind, but the construct was too heavy and costly to scale to industrial size.

In their steamroller style of engineering, where every path was tested and only the best was followed, the team scrapped that idea and went on to the next, a device that looked a little like an old World War I biplane without a cockpit. They mounted rotors at the joints where the vertical struts met the horizontal wings. This arrangement allowed more attached rotors, yet there were problems here as well. For one thing, the rotors were right in front of the wings, impeding airflow and causing a reduction in lift. And then another issue surfaced. Numerous trips to Washington, D.C., convinced Bevirt that the Federal Aviation Administration was not going to allow him to fly permanent commercial devices at 30,000 feet anytime soon. This meant that the craft would have to fly at a lower elevation—much lower.

Ironically, this brought Bevirt back to the original idea that he had sketched three years earlier on his flight back from China: a single wing facing into the wind with turbines mounted on it, gently tracing a large circle through the air. Only this time, the rotors would be mounted on posts above and below the wings, a configuration that would prevent them from stealing the air needed to keep the machine aloft. To take off and land, the whole thing would swivel vertically 90 degrees, with the rotors facing upward and acting like helicopter blades.

Bevirt was disappointed to leave behind his dream of taking wind power from the jet stream, tens of thousands of feet up, but it turns out that even at just a few thousand feet, the device could collect tremendous amounts of energy, thanks to its solid structure and constant swing. For a standard wind turbine, the amount of energy available is related to the speed of the wind and the size of the area swept by the blades. Bevirt’s prototype maximizes both these variables. The single-wing design exploits the wind to create lift, a force that sends the craft hurtling through the air at many times the speed of the wind. Even in a 20-mile-an-hour wind, the turbines can move through the air in excess of 100 miles an hour. And even though the blades are much shorter than those on ground-based wind turbines, they cut through more wind because the craft flies in a giant circle.

Bevirt says the design was less a sudden inspiration than a slow, forceful evolution. “Innovation is messy,” he states, noting the Stanford engineering mantra of FFF, or Fail Forward Fast. “You have to be tolerant of failure and learn from it as aggressively as you can. The faster you can try out ideas and learn from them, the better—and that’s especially important when exploring a new space.”

Joby energy now employs 20 engineers—mostly young men who do not mind Bevirt’s brutal 60- to 80-hour workweeks—and is trying to scale up to a prototype that is the length of a pool table and has four spinning turbines. The team has produced a few kilowatts of electricity with initial models and is designing turbines that could generate 250 kilowatts each (similar to some of the early, land-based turbines).

Although Bevirt still insists that wind turbines can fly in the jet stream, he accepts that the first units will probably have to operate at just a few thousand feet to prove they can be trusted by utility companies and big-time energy spenders. The government would probably need even more convincing. “It’s a meaty regulatory challenge,” says Bevirt, who estimates it would take $100 million and three to five years of lobbying to open up the jet stream for energy use. Energy insiders like Lukas Gresnigt, head of business development at the Norwegian energy giant Statkraft (one of the few companies following the technology), says trust will start to come only if someone can fly a half-megawatt device for at least six months without incident.

This brings up what Bevirt calls his biggest engineering hurdle. In order for high-altitude turbines to work, they must have automated control systems that can guarantee the device won’t crash in a dramatic and expensive accident. “That’s the crux of this problem,” he says. “If there’s going to be something that makes or breaks an airborne wind turbine effort, it’s going to be in controls.”

A device the size of a bread box is actually more difficult to control than one the size of a pool table, like what Joby Energy is now working on. But the consequences of a crash for the latter are obviously worse. For a device the size of a semi truck, the risk is greater still. Each device will have an onboard computer (similar to the kind used by a Predator drone) that will detect small changes in the wind and automatically adjust to them. And this is the task facing most of Bevirt’s employees today: writing code and creating control software. The crew is currently working on 3- and 10-meter-long prototypes, although the goal is a 60-meter [200-foot] commercial machine. A pilot project comprising multiple 20-meter craft flying in unison is planned for 2012.

Among the companies that are competing to tap high-altitude winds, Joby Energy stands out for its business savvy and stable funding. Even so, few players in the energy world are ready to bet on flying turbines. But you would never know about all that skepticism from walking around Bevirt’s busy compound in the woods. “JoeBen lives for those days when he goes kite-surfing and it’s blowing really big and the waves are really big,” Scheinman says. “And everyone looks at him like, ‘Is this guy really going to do it?’ And he does it. That’s a pretty decent analogy for JoeBen’s life. He looks for the biggest days and takes out the biggest kite.”

High Fliers

Joby Energy is not the only company trying to tap high-altitude wind. Several competitors are working on related designs that could start feeding the grid within the next couple of years. Like Joby, these companies are exploiting new strong, cheap materials, advanced control electronics, and an improved understanding of upper-level wind patterns. They are also seeking a way around the resistance to land-based and near-shore wind farms, like the finally approved Cape Wind project off Cape Cod.

Makani Power employs a tethered single-wing plane, fitted with six small rotors, that sweeps out a circular path at 1,200 feet and generates up to 1 megawatt of power. The California-based company received $15 million from Google's philanthropic arm (the tech giant's largest clean-energy investment) and just secured a $3 million grant from the U.S. Department of Energy.

Magenn Power has developed a helium-filled blimp that rotates around an axle 1,000 feet in the air. Generators on both ends send electricity down tethers to the ground. Starting next summer, the company plans to take orders for a $500,000 model that produces up to 100 kilowatts.

Ampyx Power combines a glider and a ground-based generator to make its PowerPlane. As the glider darts through the air, it unwinds a long tether, creating mechanical energy that a generator on the ground converts into electricity. The Dutch firm plans to sell a 1-megawatt model by 2013. Italian start-up Kite gen employs the same concept but uses a giant kite rather than a glider to uncoil the tether.