QinetiQ downplays solar flight possibilities

Those hoping that the new solar powered Unmanned Aerial Vehicle (UAV) that last week undertook a world-beating three and half day continuous flight could prove a forerunner for commercially-viable manned solar planes are likely to be disappointed, according to experts at the company behind the technology.

UK engineering firm QinetiQ hailed the Zephyr's 82 hour 37 minute flight at the US Army's Yuma Proving Ground in Arizona as a major breakthrough in spy plane technology that heralds the prospect of continuous flights capable of providing round the clock defence surveillance.

But a spokesman for the company was quick to downplay the extent to which the technology featured in the Zephyr could be applied to other forms of aviation. "It is highly unlikely it could deliver manned flight," said QinetiQ's Douglas Millard. "The power generation would simply be insufficient to carry the payload. The Zephyr has a 18 metre wing span, but it weighs just 30 kilos – as soon as you look at any form of manned flight, the power to weight ratio will prove a major problem."

The Zephyr works by generating power during the day from amorphous silicon solar arrays, no thicker than sheets of paper, which cover the aircraft's wings. The power generated is sufficient to charge up a lightweight lithium-sulphur battery that allows it to continue to fly during the night – raising the prospect of continuous flight.

However, while the test flight provides evidence that zero carbon flight is feasible, Millard is sceptical that solar power can be readily harnessed for commercially-viable manned aircraft. "The issue is collecting enough solar power to maintain a heavier aircraft," he said. "We're not looking at powering manned flights because the requirements for commercial flights are very different."

Nevertheless, Millard insisted that the technologies pioneered in the Zephyr could have a major role to play in emerging green transport technologies. " Battery technology is moving ahead constantly and the power-to-weight ratio is improving all the time," he said. "That has huge implications for all kinds of technologies."

He added that while larger planes generating power from their own solar cells remained unlikely, light weight batteries, perhaps recharged using solar farms on the ground, could one day help power on board technologies and possibly even provide power for an aircraft engines.

Others, however, are more optimistic that solar technology can play a major role in helping to deliver commercially viable zero carbon flight.

Swiss adventurer, Bertrand Piccard, is working on a manned aircraft in which he hopes to undertake the first round-the-world zero carbon flight. A test flight of the Solar Impulse aircraft – which would have a wing span as wide as an airbus, but only carry one person – is due to be undertaken next year with the round-the-world attempt scheduled for 2011.

Piccard has said that the long term goal of the project is to increase the efficiency of the solar and battery technology to a level where a solar-powered plane could carry "a few hundred passengers".

The project has also secured support from the International Air Transport Association, which has identified solar technology as one of the approaches that could help its meet its target of delivering commercially viable zero carbon flight by 2050.