Courtesy of DigiSky
The SkySpark is a proof-of-concept series hybrid electric conversion of an Alpi Aviation Pioneer 300 airplane, with a hydrogen fuel cell system as range extender (RE) to augment electrical power from the battery pack.
Project status: the SkySpark has fuel cell system components onboard, but has only flown (in June 2009) under battery power.
Intro to SkySpark
SkySpark Press, Other Info, and Videos