If you weren't so worried about having a reasonably-sized airframe or high speed we're getting pretty close to significantly increased duration/range via solar.

If you weren't so worried about having a reasonably-sized airframe or high speed we're getting pretty close to significantly increased duration/range via solar. http://thundergull.com/specifications.htm http://thundergull.com/specifications.htm It's got 95sqft of wing and a top speed of 63mph. Drag is usually with velocity squared so going 1/2 as fast might only require 1/4 as much power. They state in the article that it takes 10kw to fly level. With 100sqft and an average 10W/sqft you're at 1kw. But cut the speed down to 30mph (2500W) and double the wing area (2000W) and you're very nearly at breakeven. The 11kw battery might then last you 10+ hours after accounting for the power required to climb out. Yes it'll end up being much more of a power glider than a "proper" airplane but that might be a lot of fun.