The Swiss designed and flown Solar Impulse prototype HB-SIA powered only by solar energy - has commenced on a long distance flight across the USA departing Moffett Field in San Francisco this morning for Phoenix Arizona on a flight expected to take around 19 hours to complete

If successful it will be the first zero-fuel aircraft to have done so - the upper surfaces of the wings and stabiliser are covered with an array of 12,000 solar cells that directs excess charge to lithium-ion batteries that are used to power the 4-electric motors during non-daylight flight