The NASA Green Flight Challenge was held in Santa Rosa, California, hosted by the CAFE foundation. (Comparative Aircraft Flight Efficiency.)

Pipistrel Taurus G4 flew nearly 200 miles non-stop while achieving 403.5 passenger MPG. At the time, this was the longest flight of any electric aircraft.

More about the the G4 aircraft and history can be read HERE.
More about the NASA CAFE GFC can be found HERE.