It's a pipe dream $-wise, but I'd love to build a diesel hybrid tadpole trike. Here's my idea.
Four parallel wired ultracapacitors (each weighing 54lbs, 55Wh, 75V, 50A continuous, 150A 5sec peak)
http://www.maxwell.com/ultracapacito...12179_rev3.pdf
Diesel genset, ideally something like this 260lbs unit, running at 72V:
Model 6250 Alternator with Lombardini LDW 903 FOCS
Power the wheels with a WarP 9 motor and a Kelly 500A controller with regen, running at 72V. If I could keep my vehicle weight under 1200lbs and a cd around 0.25, then the acceleration shouldn't be too gimpy. The capacitors should be able to soak up the regen power readily and provide all the current I need (by both motor and controller limits)
What are your thoughts?