Solar Impulse 2 lands in Seville, four days after setting off from New York, using solar panels and batteries to finish latest leg of its round-the-world journey

Solar Impulse 2 has completed the first ever crossing of the Atlantic by a solar-powered aeroplane, landing in Spain early on Thursday morning.

The four-day trip, which started in New York, was the latest leg of a round-the-world journey due to end in Abu Dhabi.

During the crossing, pilot Bertrand Piccard spotted whales breaching the waters beneath and an iceberg that had floated south from the Arctic. The purpose of the circumnavigation is to showcase the capabilities of clean, renewable energy.

“The Atlantic is the symbolic part of the flight,” said Piccard, speaking to the Guardian from the cockpit a few hours before landing. “It is symbolic because all the means of transportation have always tried to cross the Atlantic, the first steamboats, the first aeroplane, the first balloons, the first airships and, today, it is the first solar-powered aeroplane.”

“But the goal is not to change aviation, as Charles Lindbergh did, but to inspire people to use [renewable] technologies and show people they can use these technologies every day to have a better quality of life,” he said.

The Solar Impulse 2 has a 72m wingspan, wider than a Boeing 747, and carries over 17,000 solar cells. During daylight, the solar panels charge the plane’s batteries, which make up a quarter of the craft’s 2.3 tonne weight. The pilot also climbs to 29,000 feet during the day and glides down to 5,000 feet during the night, to conserve power. The plane flies at about 30mph, although it can go faster if the sun is bright.

The flights are planned carefully to ensure clear weather but crossing the Atlantic was still challenging, Piccard said, having crossed turbulent cold fronts and dodged clouds. The crossing was a personal challenge too, as Piccard flew solo, taking only short naps in the unheated and unpressurised cabin, with the single seat doubling up as a toilet.

“When I flew around the world non-stop in a balloon with Brian Jones, we were two in the capsule, there was a lot of space and it was heated, so in that sense it was easier,” he said. “It is more challenging when you are alone: you can rely on the team on the ground by satellite phone, but otherwise it is up to you. But a lot of emotions come through and it triggers more courage, so I love this flying solo.”

“Every minute is a minute of suspense, a minute of challenge, and the fact I can stay [airborne] without fuel or pollution for four days and four nights is something so new,” he said. “I have the impression I am in a science fiction story and it’s like I am already in the future. And then I look outside and I say, well it’s not the future, it’s now.”

Piccard said that while Solar Impulse 2 could fly perpetually, the endurance of the pilot is limited and he has alternated the legs of the round-the-world trip with another pilot, Andre Borschberg.

Borschberg flew the longest leg, 4,000 miles over the Pacific from Japan to Hawaii. The 118-hour leg smashed the record for the longest uninterrupted journey in aviation history.

Piccard and Borschberg, both Swiss, are seasoned adventurers. Piccard made the first non-stop balloon flight around the world in 1999, while Borschberg, a former Swiss Air Force fighter pilot, has had brushes with death involving an avalanche and a helicopter crash.

The journey has not been without difficulties. Crosswinds in China caused weeks of delays in 2015 and overheating of the batteries during the Pacific crossing, forced the plane to spend the winter inside a hangar in Hawaii. The team also overcame financial troubles in 2015 after raising €20m from sponsors.

Solar Impulse 2 started its round the world journey in March 2015 in Abu Dhabi. The date of return to its starting point is as yet uncertain and will depend in part on weather conditions.