NO VA

     This week's edition of NOVA recounts the story of the solar powered flight around the world of the Solar Impulse aircraft.  There's no question it was an impressive technical feat that had to successfully exploit the bare ragged bleeding edge of technological possibility.  What it was not was a significant milestone in solar powered vehicles.
     It was a stunt, pure and simple.  A stunt which has no bearing on the world of either general or commercial aviation.  There has been some progress in electrifying small general aviation aircraft, but it will be limited to just that category, in tiny numbers.  What we will never ever see is solar powered aircraft, small or large, dotting the skies.  We will see fusion powered airliners before we see solar powered versions of those workhorses.  That is we won't unless engineers can contrive to build airliners with a square mile of wing that can travel at 500 miles per hour.
      It is conceivable, barely, that electrical energy storage technology could advance to the level of powering airliners, but simple physics prevent this from being achieved with solar power, period, not going to happen.  The founder of the Solar Impulse project has stated that it was not "necessarily about aviation" but rather about promoting the use of sustainable energy.  A publicity stunt in other words, that cost donors tens of millions of dollars.
     It did have a high techno-geeky cool factor, but that's what the crowds that showed up to gawk at the huge craft were interested in, not the sustainability boilerplate offered by the founder and pilots.  It would have been a heck of a lot more meaningful if the project had not fixated on an area in which direct solar power has no future whatsoever.
     Neither will it have an impact on ground transportation.  Sure gigantic state sized solar and wind farms might, emphasize might, be able to provide electrical power for a large fleet, but direct mobile solar power will not.  No amount of technological wizardry will be able to extract more solar energy per square inch than that provided naturally by the Sun.
     The Solar Impulse required two thousand square feet of advanced solar panels to provide enough energy to fly no faster than about 40 m.p.h. and charge its onboard batteries for use at night.  The top of an automobile covered with solar cells might provide enough power for a short drive once a week, and even if the efficiency of current cells increases dramatically that will not change.  Electric cars--already done, electric small planes--in development but will largely remain novelties, electric airliners--not bloody likely unless battery capacities increase by three orders of magnitude, and doubtful even then.   Directly solar powered transportation?  If you invest in it you will have chosen poorly.

      Addendum, Jan, 2025.  Since this piece was written there have been a number of attempts at building pure EV short-hop small passenger planes with ranges of up to 150 miles.  To date none have entered commercial service.  There has also been a proliferation of large drone-like craft being pitched as "air taxis" for very local flights.  Also none are in commercial service.  

     Despite EV incrementalism, the fact remains that there will be no pure EV 600 mph 10,000 mile range airliners or private jets in our lifetime, and not in our grandchildren's lifetimes either  Current large turbofan engines are simply too powerful and too efficient to abandon as prime movers.  The fuel for those future airliners may change, but their engines will remain largely the same.