Flying on sunshine: Solar Impulse 2 in round-the-world flight

Fuelled only by the sun - lithium batteries store energy for use after dark - Solar Impulse 2 is about a quarter of the way through its circumnavigation of the globe, a four-month endeavour that is scheduled to touch down in Abu Dhabi in July. If successful, it will be the first solar-powered plane to complete the trip, an engineering triumph and inspiration for carbon-neutral travel.

It's a test of both man and machine. With room for only one person in the cockpit, the plane's Swiss pilots, Bertrand Piccard and Andri(C) Borschberg, must alternate each leg of the mission, taking the helm for up to five days each. Borschberg says the key is self-hypnosis, meditation and power naps: "We sleep only over the oceans, for safety reasons, for a maximum of 20 minutes." The pioneering spirit is in Piccard's blood: "my grandfather was the first man in the stratosphere, my father was the first man to touch the bottom of the Mariana trench," he says.

Photographs will be added as the mission continues.