A record-breaking attempt to fly around the world in a piloted fixed-wing aircraft using only solar power has got under way. The flight is being made by Swiss aeronaut Bertrand Piccard (who co-piloted the first balloon to circle the world non-stop) and fellow Swiss, André Borschberg. The aircraft, called Solar Impulse 2, took off from Abu Dhabi, United Arab Emirates, at 07:12 local time, 9th March 2015, bound for Muscat in Oman, with André Borschberg at the controls.

The Solar Impulse project has already set a number of world records for solar-powered flight, including a first crossing of the United States in 2013. The round-the-world flight required the construction of a larger plane than the prototype, Solar Impulse 1. With a wingspan of 72 metres (236 feet, wider than that of a 747 jumbo jet), Solar Impulse 2 was built and first flown in 2014. It was fitted with 17,000 solar cells, which line the top of its wings, along with a set lithium-ion batteries that it will use to power night-time flying.

The four motors that drive the aircraft generate about half the power of a racing motorbike. But, unlike normal aircraft engines, which lose around 70% of their energy through heat, Solar Impulse's motors lose only 3%. Energy efficiency of this kind is, many scientists say, the single cheapest way to reduce carbon emissions across the world.