Solar Impulse Pilot Prepares for Historic Journey Across the Atlantic Ocean

ABC News goes inside the hangar with pilot Bertrand Piccard.

— -- Solar Impulse, a solar-powered airplane being flown by two alternating pilots, will soon take off on a transatlantic flight -- one of the most grueling legs in its attempt to circumnavigate the world.

Swiss adventurers Bertrand Piccard and Andre Borschberg have been taking turns flying the one-seater airplane, which is solely powered by the sun's energy.

"The Atlantic is always the symbolic flight for all the means of transportation and today it becomes a symbolic flight for energy vision," Piccard told ABC News today at the hangar. "It is the first time an airplane flying solar -- that means with electric engines, zero emissions, zero fuel -- is attempting to cross this ocean from America to Europe, so it is extremely exciting for all of us."

Solar Impulse is able to fly at night and in cloudy weather because it stores solar energy in batteries on the aircraft.

"During the day flight, the sun gives enough energy to run the four electrical motors and to charge the batteries so during the night we have the batteries running until the next sunrise and that next sunrise we recharge for the next day and like this we can fly forever," Piccard said.

During the crossing, which is expected to take four days, Piccard, who is also a psychiatrist and trained in self-hypnosis, will take 20-minute naps in the pilot's seat as he cruises across the ocean going about the same speed a car would on the highway.

Solar Impulse has the wingspan of a Boeing 747 but is as light as an SUV. Space inside it at a premium, so the cockpit seat can also be converted into a bathroom. Meals, such as mushroom risotto, come in packets that don't take up much room.

Piccard, who previously circumnavigated the globe in a hot air balloon, said while that adventure felt personal for him, the one he's been on for the past 15 months with Solar Impulse server a greater purpose.

"When I circumnavigated the globe in a balloon nonstop flight around the world, 20 days in the air, it was my personal dream. It was a big race with Richard Branson, Steve Fossett and other teams," he said. "This Solar Impulse circumnavigation is more than a personal dream, it's a meaningful adventure. It shows what we can achieve with clean technologies."

Solar Impulse will most likely land in Spain or France after the Atlantic crossing. The two pilots expect to complete their around-the-world journey this summer in Abu Dhabi, United Arab Emirates, where the voyage began in March 2015.