http://gristmill.grist.org/story/2007/4/10/114819/769#9
Look for solid oxide fuel cell/turbofan plugin hybrid airplanes real soon.
The thing is that getting into the air takes a lot of power, cruising not as much. Given a few more generations of batteries their weight will approach the weight of liquid fuel, for the equivalent amount of energy.
A hybrid turbofan engine would cruise on battery power. The takeoff would use liquid fuel through solid oxide fuel cells that would generate electricity directly to power the hybrid turbofan. That liquid fuel could be biodiesel from algae growen in solar collectors, almost pure solar fuel.
Then the very hot exhaust gases from the solid oxide fuel cell would provide additional power by expanding through the turbine in the turbofan engine. This would yield very high efficiency, several times the efficiency of a normal turbofan aircraft engine. On biodiesel from algae grown in solar collectors, almost pure solar fuel.
When the aircraft got to cruising altitude the batteries, previously charged on the ground from renewable energy, would take over.
Solar panels on the wings? Still too heavy for actual passenger airliners, but who knows?
Maybe with an almost lighter than air helium filled silicon bubble aircraft that uses solar heat to climb then glides/flys to it's destination on direct solar electric power? By designing solar concentrators into the structure, solar cells could be 1/10nth the size and weight and operate at 39% efficiency. This efficiency with concentration has been proven at the National Renewable Energy Labratory.
A lighter than air foam made from helium filled silicon bubbles has already been developed too. And this silicon compound is extremely strong.
More cool solar flying!
http://www.blazingwings.org/entry/top-12-solar-powered-aircrafts/
