Security ... think about it!
On the other hand, the Solar Impulse -- a new Swiss solar-powered aircraft that was unveiled on Friday -- could have commercial uses (though as of yet, it only has enough space for the pilot). As we reported last month, the aircraft, which doesn't require a single drop of fuel, is designed to run on sunlight alone, as its four engines would be powered by electricity converted via the wings' solar cells. Thanks to this design, the aircraft has the potential to stick around in the air for longer than your average airliner.