The Solar Impulse stopped in our neighborhood this week and is off to continue its trip around the world. It was stuck here for five days because it was too windy for this absurd, delicate, folly to fly safely, but things have calmed down and it’s ready to resume its 30 mph odyssey. I think the whole thing is silly, though as long as people are willing to fund it as a lark or can make money from sponsorships, it’s harmless. Nothing about solar power (or aviation) is being learned from the project that could not be inferred from engineering and economic calculations. The critical constraint on such a thing, of course, is the refusal of the sun to shed more than about the power consumption of a toaster on a square yard of any surface, so to carry a pilot and his lunch, and the batteries that keep it under way (and therefore aloft) at night, the aircraft has to be (i) enormous and (ii) exquisitely delicate, pushing the limits of material science.
It is also impractically at risk from turbulence, eddies even in steady flows that can apply forces in opposite directions to different parts of the plane. This turbulence is probably the reason very large, necessarily delicate, lighter-than-air rigid craft like the Shenandoah, Macon and Akron failed. I predict that if the Solar Impulse 2 voyage fails, it will be loss of the aircraft in unexpected weather, possibly clear air turbulence and not even a violent storm.