The first nonstop flight across the Pacific, in 1931, took 41 hours. Now a group of energy and technology companies is backing an attempt by two solar flight pioneers to cross the ocean even more slowly, taking five days and nights to fly from China to Hawaii in an aircraft powered only by the sun.

The Solar Impulse 2 has an average speed of about 60 miles per hour and a wingspan wider than a Boeing 747. The upper surfaces are clad in solar panels, and batteries provide power at night.

The developers of the aircraft plan to make the first ever solar-powered flight around the world next year. The Pacific crossing is the most demanding stretch of the journey, which will take place in stages, starting next March.

The project’s backers include SunPower, the solar subsidiary of French oil group Total; ABB, the Swiss engineering group; Solvay and Bayer, the chemicals companies, and Masdar, the state-owned renewable energy company of the United Arab Emirates.

Commercial solar-powered flights are highly unlikely in the foreseeable future. Indeed, energy forecasters believe that even if renewable sources eventually replace fossil fuels for many purposes, air transport is likely to continue using oil for longer than almost any other sector, because of its superior ratio of energy content to weight.

However, André Borschberg, chief executive of the Solar Impulse project and one of its two pilots, said the aim was “not to bring about a revolution in air transport, but to bring about a revolution in people’s ideas about clean energy.”

Like the moon landings, the project had stimulated innovations that would be used on the ground, he said. “We needed better insulating materials that will go into refrigerators; we needed better batteries that will go into ground transportation. So that was the motivation of the partners.”

“Very often, we hear that climate change can be solved with less comfort, less mobility, less industry, less growth. And no one wants this: we want growth. So we need new clean technologies,” he added.

The appeal of developing a solar-powered aircraft was the degree of the challenge involved, said Bertrand Piccard, Mr Borschberg’s fellow-pilot. “If you can do this on an airplane, you can do it anywhere on the ground,” he said. “It’s the most powerful symbol, because it’s the most difficult to achieve.”

However, he said, electric aircraft using the batteries developed in the Solar Impulse project could be in commercial use, perhaps for tourist flights, within five years.

The solar panels on Solar Impulse’s wings are expected to convert about 22-23 per cent of the solar energy falling on them into electricity – a big improvement on the 16 per cent typically achieved by standard solar systems.

Those panels will generate enough power during the daytime for the plane’s four propellers, driven by highly efficient electric motors, to take it up to about 30,000 feet and to charge the batteries. At night it glides lower while batteries power the propellers.

Mr Borschberg and Mr Piccard flew an earlier version of the aircraft, the Solar Impulse 1, in stages across the US last year. But crossing the Pacific is a much more ambitious undertaking.

The aircraft could in theory fly forever without refuelling, but it will need to stop every few days to relieve the pilot. The five-day stretch across the Pacific would be the longest ever continuous flight by a plane with a single pilot, generating huge physical demands.

The pilots have been learning exercises to keep their bodies functioning while they are confined in the cockpit. They will sleep in 20-minute bursts and have learnt meditation techniques to help maintain their focus.

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