"We have a big energy problem and we have to think big," said Prof Sossina Haile, at the California Institute of Technology, who led the research.

Haile estimates that a rooftop reactor could produce about three gallons of fuel a day. She thinks transport fuels would be the first application of the reactor, if it goes on to commercial use. But she said an equally important use for the renewable fuels would be to store solar energy so it is available at times of peak demand, and overnight. She says the first improvements that will be made to the existing reactor will be to improve the insulation to help stop heat loss, a simple move that she expects to treble the current efficiency.'

Read more: Researchers Develop Reactor to Make Fuel From Sunlight