When it's in flight, there's no roar of jet engines. It's strangely quiet. And as it crisscrosses America, the spindly plane doesn't use a drop of fuel. Day, and even night, it flies on the power of the sun.
And it's that fact that has the U.S. energy secretary, and the plane's two pilots and fans around the world, so excited.
The one-man craft called Solar Impulse has been flying cross-country in short hops as part of a 13-year privately funded European project that is expected to cost $150 million.
Ernest Moniz, who heads the U.S. Department of Energy, praised the effort at a news conference Monday at Dulles International airport where the plane landed in the dark early Sunday morning. Moniz said it highlighted a cleaner energy future for the nation.
"It's also a poetic project," said Bertrand Piccard, one of the pilots taking turns flying this aircraft across the United States. "It's about flying with the sun. It's about flying with no fuel."
It's not that the experimental European plane is going to change the way the rest of us fly, Moniz said. But it may change the way we drive and the buildings we live in sooner than we think.
The high-flying lightweight technology will pay off on the ground far more readily than in the air. This project should lead to cleaner appliances, greener cars and more energy-efficient building, said Solar Impulse CEO Andre Borschberg, who also is one of the pilots.
In an in-flight interview Friday, while he was over Indiana at 30,000 feet and controlling the plane with just two fingers, Borschberg said this experiment isn't about aviation being cleaner; airplanes only produce 3 percent of the world's heat-trapping gases, he said.
"The potential is on the ground, the potential is not in aviation," he said in the interview with The Associated Press. "On the ground, the potential is huge and is readily available."
Perhaps as early as 2015, an updated version of this solar plane will be flown around the world. This year's practice runs have this prototype flying from San Francisco to New York with five stops in between. Most recently, the plane flew from St. Louis to Cincinnati and then suburban Washington. In a couple of weeks, it will make the final leg, landing in New York City.
Last year, the same plane flew from Switzerland to Morocco.
When he first came up with the idea a decade ago, Borschberg said he was told by experts: "Your project is impossible."
Now instead, Moniz said, Solar Impulse is highlighting four high-tech green energy fields that his office is trying to promote: solar power itself, better batteries that allowed Solar Impulse to fly at night, lightweight materials and integrating everything together.
They'll pay off on the ground quickly, Moniz said. Take the lightweight carbon fiber and lighter solar cells. Once applied to rooftop solar panels, that will bring down costs for houses because much of the problem currently is the size and weight of the panels, he said.
Solar Impulse carries more than 11,000 solar cells—10,746 of them on the long wing that stretches 208 feet. Although it has the wingspan of a jumbo jet, the entire plane weighs just 3,500 pounds, the size of a small car.
Seth Borenstein can be followed at http://twitter.com/borenbears