I think I discovered or came onto something a little exciting. The most efficient and cheapest way to run a petrol based car is with an all electric drive system, with a diesel based generator to charge the drive. Basically a plug-in hybrid or a GM Volt. Unlike the Honda hybrid which uses electric assist, or the Toyota hybrid that uses dual drives.

Researching the web I found diesel generators ranging in efficiency from 27 KWhs per gallon to 8 KWhs per gallon.

Assuming you can find a diesel generator at 20 KWhs per gallon. You put it somewhere on the car. Most diesel generators are made in China. You can probably find one for $1000. Whenever your battery gets low in your car, an indicator comes on. You press a button to electric start the generator. The generator stays until you turn it off or the battery is filled. If you are near home you might want to run the batteries as low as possible to charge on the grid.

The Zenn gets 124 Wh per mile. With the 20 KW h per gallon generator above you would get 142 miles a gallon. With a 20 gallon tank you would get 2887 miles before you would have to refill.

The Prius in electric mode gets say 200 Wh per mile. It would get 100 miles a gallon, or a 2000 mile range.

Sounds like a good plan. Make it, and put "EVcast" on the side and we will be your sponsor (assuming sponsorship is about $100 - that is our sponsorship budget) :)

I spent all day researching diesel generators efficiency. It is probably safe to say you can get 10 KWh/gallon, I am not convinced of higher efficiency as most probably lie a little bit. Do the math I found some at 15 KWh/gallon (some even higher) but I am suspicious.

However there is a another little problem the Zenn 120 Whr/mile is most likely at 25 mph. At 75 mph, even the CityZenn would consume far more, maybe 300 Wh/mile. To keep a car going at that speed would be 22.5 KW. The problem is generators start to get expensive and large at that size.

This is worlds most effient car as I can tell.

http://gas2.org/2008/03/12/the-worlds-most-fuel-efficient-car-285-mpg-not-a-hybrid/

However, It could even be more efficent if it use tech like below imho.

http://www.treehugger.com/files/2006/08/the_hybrid_mini.php

http://www.cleantechblog.com/2007/09/wright-way-to-electric-car.html