Last year, two Swiss pilots became the first to fly across the US using the power of the sun. Now they are back with an even more ambitious plan, to be announced today; to fly a more advanced, lightweight solar-powered aircraft, Solar Impulse 2, around the world early next year, beginning and ending in oil-rich Abu Dhabi in the United Arab Emirates.

The journey, like its cross-country predecessor, will not be continuous, but that’s more to meet the needs of the pilots than those of the aircraft which, thanks to an elaborate combination of solar cells and lithium batteries, can fly day and night. Ocean crossings On the previous trip, the men flew roughly 24 hours before stopping. But this time the pilots – who will alternate on the the roughly dozen legs of the trip – must fly for up to five days and nights at a time because of the ocean crossings.

“We trained in the simulator for longer times, for three or four days, but, of course, we never flew, that’s going to be the first time,” said André Borschberg, one of the pilots. “You need an airplane which is reliable; you cannot do the maintenance in the flight.”

The men's mission has drawn support from dozens of entrepreneurs and companies, including Masdar, Abu Dhabi's renewable energy company, and is meant to be a grand demonstration of the possibilities of clean energy. Practical technologies But it has also become an unlikely incubator of more practical technologies, including a thin insulation that can allow refrigerators to have more internal space and a product developed with Nasa that makes urine drinkable.

A way of producing oxygen with solar energy is also under development.

Remarkably, one of the biggest commercial applications for the aircraft could be as a kind of satellite replacement, making it into a sustainable high-altitude, unmanned platform with cameras or communications equipment. – The New York Times