Business Green: Boeing has confirmed that it is working on a space-age plane design that could keep flying for up to five years using only solar power. The company revealed earlier this month that the US Defense Advanced Research Projects Agency (DARPA) has signed an $89m (£56.5m) deal with Boeing that will see it develop and fly the aircraft on its first demonstration flight by 2014. The spyplane will be designed to fly at altitudes of 60,000ft (18,288m), constantly collecting information and …