It doesn’t make good business sense, physics sense, or much of any kind of sense, to try to fly an airplane on solar power. Not yet. With the state of the technology, and how relatively young the solar sector still is, such an endeavor would be considered quixotic today—let alone in 2003, when Bertrand Piccard and André Borschberg, co-founders of Solar Impulse, announced they would design a solar-powered aircraft and fly it around the world. It would be a statement, they said, about our global dependence on fossil fuels and the untapped promise of burgeoning green technologies. The Swiss pilot-entrepreneurs were after "perpetual flight": a plane that could climb to 9,000 feet and fly on the sun's energy by day, then descend below cloud cover to lower altitudes, where it would cruise on stored battery power by night.
It was a long shot. And yet seven years of innovation later, the 70-person Solar Impulse team is nearing its goal. “We were intrigued by this notion of perpetual flight,” said Borschberg when visited in September in Solar Impulse’s massive hangar, situated smack in the middle of Düendorf Airfield, a Swiss military zone. “We wanted to be totally independent of any fuel.” Forget hybrid planes, or the biofuels fixating most of the sustainable aviation sector today; Piccard and Borschberg are purists. “No fuel, no CO2, no pollution. It could fly almost forever, assuming good weather,” Borschberg said of their invention.
By November of last year, test pilot Markus Scherdel—formerly of DLR German Aerospace, the NASA of Germany—was climbing into the cockpit of the coleted prototype to taxi down the Dübendorf runway for the first time. Soon after that, Scherde was back in the cockpit, this time guiding the plane not just down the runway but up into the air for a series of successful “flea-hop” mini-flights over the tarmac. (You can watch a film of the event on YouTube.)
The Solar Impulse HB-SIA, as it is officially named, is a strange sight to behold. Resting under the sky-high ceiling of its hangar at Dubendorf, it looks fragile to the point of breakable. And no wonder: HB-SIA, comprised of a carbon skeleton covered in a flexible polycarbonate “skin,” weighs only about 1.5 tons, about as much as a small car. Its wings are so light that a single person can carry them. And when I tested both the pilot's parachute and the detached nosepiece of a second prototype of the plane for weight, the parachute was heavier.
The HB-SIA carries a minuscule, one-person cockpit, and its generous 64-meter wingspan (which is comparable to that of an Airbus) makes it aerodynamically efficient and affords it a low sink rate, so that it needs very little energy to continue flying horizontally. This greater wingspan also creates maximum surface area for the aircraft’s 650 square feet of crystalline solar cells—all of which provide a maximum of about 40 kilowatts, or the power of a small scooter or motorcycle, and should get HB-SIA up to speeds of 45 miles per hour on sunny days.
While 45 miles per hour is practically the speed of light for a vehicle powered exclusively by the sun, it’s slow as molasses by today’s aviation standards (the average commercial plane cruises about 12 times faster), so each leg of HB-SIA’s transcontinental journey will take a full five days and five nights. Piccard and Borschberg still haven’t quite figured out how they’ll manage to take turns living in a one-man cockpit for such lengths; they’ve hired a yogi and a sleep specialist to help troubleshoot few human details like how not to fall asleep at the throttle, pass out from boredom, or die of thrombosis between takeoff and landing. As for energy storage, HB-SIA’s lithium batteries, which make up one quarter of the plane’s total weight, are two times lighter (but twice as efficient) as the batteries used in most computers, and have the storage capacity to power HB-SIA through eight hours of darkness each night.
Every last nut and bold in the plane, from its electric engines to it batteries to its solar cells, has been designed specifically for Solar Impulse, and that innovation has come at a price. Of Solar Impulse’s $100 million budget, about $55 million has been spent so far, primarily on technology development and salaries. Most of that funding has come in via principle partnerships with three corporations: Solvay, an international chemical and pharmaceutical group; Swiss watchmaker Omega; and Deutsche Bank.
Currently, HB-SIA is being dismantled at Dübendorf Airfield and prepared for transport to Payerne, where it will be reassembled and readied to execute a 36-hour, day-and-night test flight sometime this summer. That flight will put Piccard and Borschberg one step closer to their ultimate goal, a round-the-world-flight, which they hope to complete by 2012.
Borschberg, for his part, is an MIT graduate, an alumnus of the consulting firm McKinsey, and an entrepreneur. Biceps bulging from his company polo shirt, hair slicked back, he looks as though someone built him for maximum efficiency, just as he himself has built HB-SIA. “There is no space for doubt; there is just time in fact to be focused,” he told me flatly when I asked if he ever thought their mission might be a little audacious.
Confident and tenacious though they might be, Borschberg and Piccard are in no rush to make solar aviation commercially feasible. For now, they say, Solar Impulse’s flight around the world should be viewed like the Wright Brothers’ or Lindbergh’s first flights; the pioneers of aviation didn’t set out to deliver 150 tourists and business travelers from New York to India, but merely to show that it was possible to fly. “The first step is to demonstrate that this is possible, then we can open up and develop applications,” said Borschberg. “For us it’s important to show what we can do with this technology, so it’s more a first step. It’s more a symbol than an end product.”
The aviation industry seems to agree that the future of solar technology in commercial airplanes does not look bright, at least not in the near term. Not a single member of the General Aviation Manufacturers Association is currently researching or developing solar technology for planes. Boeing, highly active on the sustainable aviation scene, has several staffers in top positions at the Commercial Aviation Alternative Fuels Initiative and is a driving force behind innovation in fuel cell technology for airplanes. But even they are leaving solar-powered flight alone, for now. “Solar isn't something we're actively pursuing for commercial air travel—the energy density we would need from the solar cells simply isn't there, and the trade-offs are too great,” said Boeing press officer Terrance Scott.
Today, almost everyone who is looking forward to the aviation fuel of tomorrow is looking not up at the sun, but down at the ground, to biofuels. Nate Brown, deputy director of CAAFI and policy analyst for the Federal Aviation Administration’s office of Environment and Energy, says that fuels made from plants like jatropha (related to castor oil, it thrives even in tough, dry environments and may prove critical in places like India and Africa), camelina, salicornia, and algae look most promising from where he’s standing today, but the jury is still out as to which biofuels will prove most feasible, energy-efficient, environmentally friendly and safest for airplanes.
Carl Burleson, acting deputy assistant administrator for the FAA’s Department of Policy, Planning and Environment, goes further. He says that even within the biofuel sector, the industry is really only looking at “drop-in fuels,” or fuels that could theoretically be poured straight into the engines of today’s fleet, with no modifications required. “Early on we looked at the idea of hydrogen, the idea of ethanol, various things that would involve redesigning today’s fleet, and just decided it wasn’t a very viable approach because you have such a large embedded capital cost right now in today’s fleet,” said Burleson. “If you were going to design a hydrogen aircraft, if it were viable, they would be substantially different in design, so even if you get it right you’re talking 30-40 years to change over the fleet.”
Several airlines have already run test flights on biofuel; the advances have been minimal, but a great deal of manpower and funding are currently pouring into research and development. Meanwhile, as the aviation industry (which knows it will eventually need to graduate from fossil fuels, for both economic and environmental reasons) considers biofuels the first step, Borschberg and Piccard are already leaping headlong several steps past that. Borschberg says the biggest lesson that he and Piccard have learned from the pioneers of aviation—the Wright brothers and Lindbergh—is that “if you don’t try, you’ll never succeed.”
“There were people in the U.S. who were able to demonstrate in 1903 that it was impossible to fly,” Borschberg likes to point out. “We prefer to spend time to make it possible rather than spending time trying to demonstrate that it’s not possible. It’s more interesting.”
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