Flight actually scales up really well.  Double the volume means less than double the energy required. So, larger craft can get a better cargo to energy efficency and or more speed.<p>Solar impulse is large, but light and can carry two people plus stuff.  Keep scaling it up, ditch the pilot, and you can have something between big slow boats and fast, but expencive jet aircraft.  A full 50,000 lb 20&#x27; shipping container and 1 week China to US is probably viable.  (Boats take 2 week to 1 month and unload at ports.)