Photograph by Jean Revillard, Solar Impulse2/Getty
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The Solar Impulse 2 flies around Egypt's pyramids shortly before completing the final leg of its trip around the world.

Photograph by Jean Revillard, Solar Impulse2/Getty

Historic Solar Flight Shows Promise and Challenge of Clean Energy

Completing the first trip around the world exclusively on solar power, the experimental Solar Impulse shows what’s possible in energy and flight.

The Solar Impulse 2 concluded its journey Monday, becoming the first aircraft to circumnavigate the globe without a drop of liquid fuel. And while we won’t be boarding sun-powered commuter flights anytime soon, the solar plane’s feat does point toward the future of energy.

Pilots Bertrand Piccard and André Borschberg made the trip during 17 months, stopping in 17 cities. Sun power propelled them across approximately 26,718 miles (43,000 kilometers). Their landing in Abu Dhabi happened one day after the birthday of Amelia Earhart, who became the first woman to fly alone across the Atlantic in 1932.

The historic flights join earlier ones by Earhart, Charles Lindbergh, and other pioneers—but Solar Impulse was always more about energy than aviation.

Outlining his vision for the project 12 years ago, Piccard noted that clean energy “lacked really dynamic promotional marketing impetus.” Solar Impulse, then, is an airborne mascot for the technologies its backers say can cut the world’s energy consumption in half and protect a warming planet. (See more photos of the voyage.)

“Impressive” Achievement

The Solar Impulse assembled a number of technically advanced components in a way that wouldn’t have been possible years ago, says Craig Steeves, associate director of the University of Toronto Institute for Aerospace Studies.

“I certainly think it’s a pretty impressive technical achievement,” he says. “They’re pretty far ahead on a path that the aerospace industry would like to go.”

That said, solar-powered commercial air travel at the capacity and speeds we expect isn’t feasible, “certainly not in my lifetime,” Steeves says. Solar Impulse can only carry one person—the pilot—and travels at about the speed of a car, 46 miles per hour (75 kilometers per hour) on average. (Learn about the secrets of the flights.)

“A lot of what they're demonstrating,” Steeves says, “is probably going to be relevant to earth-bound applications before it becomes important to flight.”

Indeed, the plane’s lightweight materials and other components could be used on the road and the power grid. Its super-efficient engine ran on electricity generated from 17,248 solar cells. Special, energy-dense batteries stored sun power so the plane could fly at night.

“Solar Impulse has proved that a 24-hour electrical system, powered exclusively by renewables, is possible,” says Conor Lennon, manager of special projects with ABB, which makes electric transformers, EV charging stations, and other power technology.

Four ABB engineers were embedded on the Solar Impulse project, Lennon says, working in part to extract maximum power from the solar panels and keep batteries fully charged. The plane’s cells are nearly 50 percent more efficient than regular ones.

An Electrifying Flight

Masdar, the sustainability testing ground located in Solar Impulse’s beginning and ending destination, also supported the journey. “In Abu Dhabi, you can feel the excitement surrounding Solar Impulse,” says Masdar CEO Mohamed Jameel Al Ramahi. “Being the host city is a source of tremendous national pride.”

In particular, Al Ramahi says, the plane’s 118-hour flight over the Pacific Ocean “shattered the myth that solar energy captured by PV panels can’t be stored and utilized at night.”

Here again is where Solar Impulse stands for advances that will more likely appear first on the ground, as power plants look to introduce more renewable energy onto the grid while balancing the intermittent nature of the sun and wind.

“We are working to crack the code on how to make solar a baseload provider of energy,” Al Ramahi says.

The plane’s efficient engine can serve as a model for other motors, the Solar Impulse team notes, while its lightweight, extra potent LED lighting and insulation can be used in housing. Its sensors and data-collecting tools, meanwhile, could help inform other types of energy management systems.

And while much of the tech aboard the Solar Impulse may be better employed on the ground for now, the aviation industry is working on similar light materials, smarter controls and other efficiency improvements.

Dan Rutherford, program director for marine and aviation technology at the International Council on Clean Transportation, sees the Solar Impulse as a good emissary for clean-energy awareness, but echoes Steeves in saying we won’t be seeing solar-powered commercial flights anytime soon. He notes that Solar Impulse is not just about the solar power: It’s also about using electricity instead of combustion and hydraulics.

“We’ve already seen a movement toward more-electric aircraft,” Rutherford says, pointing to the Boeing Dreamliner, which has batteries that power its auxiliary system and computers.

Between the envelope-pushing advancements boasted on the Solar Impulse and the most advanced commercial planes going into service today, he says, “definitely you are seeing an overlap.”

On Twitter: Follow Christina Nunez and get more environment and energy coverage at NatGeo.