"Because you look at the sun, you see your props turning, and you think 'Wow, that's really magic,'" the Swiss pilot told CNN via satellite video from the cockpit.
The aircraft took off Monday from New York's John F. Kennedy International Airport in the first attempt to fly a solar-powered aircraft across the Atlantic Ocean.
The cross-Atlantic flight is likely to be one of the most grueling legs in the aircraft's ambitious around-the-world journey, devised to raise awareness of the power and potential of clean-energy technologies.
Weather conditions over the Atlantic are notoriously unstable, with fast-changing winds a pilot's greatest enemy.
Almost eight hours into the flight Piccard was some 3,000 feet into the air between Boston and Nova Scotia in the fixed-wing plane that travels at the speed of a regular car. The plane is built with a wingspan wider than a Boeing 747 and doesn't rely on fossil fuel at all. Its four electric engines are powered by more than 17,000 solar cells built into its lightweight, super-strong carbon fiber wings.
Piccard, a Swiss national who is a trained psychiatrist and balloonist, is expected to fly between 90 and 110 consecutive hours before landing in Seville, Spain. He is prepared to land in various French cities if the weather makes things difficult for him.
But to Piccard, the longer the flight, the better.
"For an airplane that has endless endurance, you want to do the (most) you can," he said.
Piccard sent a series of tweets after takeoff, including one just as he hit the Atlantic.
Little house in the sky
He will soon climb to 28,000 feet and continue at that altitude until the night.
Piccard has been preparing for the flight for "years and years," saying he'd been long inspired by the pioneers who wanted to cross the Atlantic to prove their way of transportation was mature.
"I met (American aviator) Charles Lindbergh when I was a child. I saw the balloons, the airships, the hot air balloons, steamboats -- you know, every means of transportation wanted to cross the Atlantic, and now for the first time it's a solar-powered airplane," he said.
Piccard's routine for the flight would seem exhausting to most. But he is little bothered by having to sleep in 20-minute naps, waking up after each one to check the controls. This will go on for at least four days.
"During these days and nights, it's a little house in the sky. I eat, I warm up my food, I have (a) toilet, I can recline the seat to be able to sleep," he said, sounding at home in the cockpit.
But at higher altitudes, he must use an oxygen mask to breathe, which he said was the tiring part.
"What I'd like to show with my team is that clean technology today is showing incredible goals. You can fly now longer without fuel than with fuel, and you fly with the force of nature, you fly with the sun. It's the new era now for energy and this is really what we'd like to inspire people to do," he said.
Piccard described seeing a school of whales, adding that flying has given him a greater appreciation of nature.
The Solar Impulse 2 project is the brainchild of Piccard and Andre Borschberg, a Swiss engineer and businessman. The aircraft is a single-seater, so the two men have shared the flying by taking different legs of the journey.
The plane -- powered 100% by the sun -- has so far completed 14 legs, starting with a flight from Abu Dhabi, United Arab Emirates, to Muscat, Oman. The aircraft then hopped through Asia before a lengthy leg across the Pacific Ocean to the United States.
Borschberg flew the plane from Nagoya, Japan, to Hawaii last July in a leg that took just under 118 hours. That flight marked the first oceanic crossing for a solar-powered plane.
After crossing the Atlantic, Borschberg is scheduled to fly to Egypt, and Piccard will likely to do the final leg from there back to Abu Dhabi by late summer, completing a 43,000-kilometer (27,000-mile) world trip.
When Piccard arrives in Seville, sleep will not be the first thing on his mind. He will first thank his team and get ready for the next flight.
"We are on our way around the world, so the Atlantic flight is an iconic flight, but it's not the only one," he said.
"Hopefully and successfully (we will) finish the flight around that world that we started last year."
The journey so far has not been easy. It began in March 2015 in Abu Dhabi, and the project's team has encountered several problems. The plane faced a series of weather delays in China that slowed progress for weeks, a hiccup followed by an unexpected diversion to Japan, where a storm damaged the aircraft on the tarmac.