A solar-powered plane has completed the first leg of a round-the-world flight. The plan is to eventually circumnavigate the globe without ever using fossil-derived fuels.

The plane, Solar Impulse 2, started with a short leg, flying the 500 miles from Abu Dhabi to Muscat in around 12 hours.

The journey isn’t even close to non-stop. It’s scheduled to take around five months, during which it should total around 25 days of flying time. The route will go across India, China, the US and either southern Europe and Northern Africa. It’s not quite at the Equator, where sunlight availability could be maximized, but there would be less land available to break up the journey into shorter legs.

As well as the land issue, flying over the Northern hemisphere also fits in with the planned timetable, which covers the months with the longest hours of daylight. Although the summer solstice doesn’t fall in the middle of the schedule by time, there’s a planned one month break in China so that the Pacific crossing benefits from the longest days. The break also gives some wiggle room if any earlier legs are delayed.

The plane is designed to carry 17,000 solar cells, placed across the 72-meter wingspan. While that’s wider than a 747 jet, Solar Impulse weighs less than one percent as much as the 747, a mere 2.3 tonnes. That’s achieved through a combination of the design and having no need to carry fuel.

The solar cells will provide instant power for four electric motor-driven propellers. They’ll also charge four lithium power batteries to be used during nightfall.

The biggest challenge is almost certain to be the crossings of the Pacific and Atlantic, which are expected to take around five days apiece. While the plane should have enough fuel to make that trip, it will be a feat of endurance for the pilot. Two men, Andre Borschberg and Bertrand Piccard, will share duties across the entire trip, but only one will be in the plane for a particular leg, including the lengthy ocean flyovers.

Whilst flying, the pair will be unable to stand. They plan to take ‘catnaps’ while flying the longer legs, with a proposed schedule of 12 breaks of 20 minutes during every 24-hours period. They’ll wear goggles which flash lights to wake them up at the end of a break, plus armbands that vibrate if anything needs immediate attention such as the plane going off a level course.