Manned flight doesn't seem to be a good application for solar aircraft given the weight and speed limitations. Solar drones seem a much better fit. Airbus seems furthest along with their Zephyr [0], it has stayed aloft for 14 days (!). They are targeting the military as a customer and are marketing it as an alternative to a satellite, that is, an indefinite surveillance capability.<p>Facebook has a similar program, Aquila, which is aimed at providing internet access. They just recently had first flight of a full scale version [1].<p>[0] <a href="https://airbusdefenceandspace.com/our-portfolio/military-aircraft/uav/zephyr/" rel="nofollow">https://airbusdefenceandspace.com/our-portfolio/military-air...</a><p>[1] <a href="http://arstechnica.com/information-technology/2016/07/facebook-tests-full-scale-solar-powered-internet-drone/" rel="nofollow">http://arstechnica.com/information-technology/2016/07/facebo...</a>
Things get interesting when we cross the inflection point of having an abundance of lift.<p>Once you can achieve X+Y lbs of indefinite lift, where X is the necessary weight and Y is the excess, then maintaining Y*C aloft indefinitely becomes simply a matter of scaling the number of crafts to contribute the requisite excess lift (aerodynamics aside for the time being).<p>What affect will indefinitely floating object, barges, buildings (living, restaurants, business), etc... have on society where fuel isn't a factor? (e.g., Facebook's global internet, cheaper flying transports, cars and eventually domiciles)
This is less a plane, and more of a battery with wings. The amount of cargo a solar plane could carry is minuscule.<p>Limits to battery energy density means that we can't improve very much on this.
My bet for carbon-neutral aviation is not batteries, it's synthetic hydrocarbon fuels.<p>A factory that can make kerosene out of atmospheric carbon and electricity at a reasonable cost seems like a smaller stretch than an exotic new battery with orders of magnitude better energy density.
For the heck of it, I compared this to what it would have taken to ship the SI2 via container ship. Apparently, a container ship can move a ton of cargo 500 miles on a gallon of fuel, so to ship the SI2 the entire distance of it's trip would take about 120 gallons of fuel.<p>The container ship would have been significantly faster, taking 50 days to complete the trip, versus over 500.