Oh, you can do so much better than that. How about a combination of electric and solar/wind power?
AE-1 Silent
Launch on the electric motor, then find a thermal and soar as long as you want, using zero fuel. And you can stay up for long periods - I've gone as long as 3 hours or so in a standard air-tow launched sailplane, and could go much longer if there was an on-board restroom :-)