i know barely vanagon content.. but wow what a concept. 

The Stirling motor 
http://www.suremarine.com/whispergen.htm

Conventional generators are driven by noisy internal combustion diesel or petrol 
engines. The main feature of the Stirling motor is its silent operation, as it is 
not an internal combustion (explosion) engine: its principle is based on permanent 
external combustion. A boiler-type burner heats the outside of the cylinder heads 
of the engine to about 700�C. Pressurized nitrogen contained in the water-cooled 
engine block is pumped into the hot cylinders and pushes down the pistons while 
expanding as it heats up. This same gas then returns into the block where it cools 
down and contracts, and so on in a continuous cycle. 

Invented in 1816 by the Reverend Robert Stirling, the engine has been subject to 
lots of research but till recently no one has succeeded in developing a practical 
application that is suitable for daily use. 

Although the Stirling technology was invented in 1816, the WhisperGen 
is the first commercially available product incorporating a Stirling motor.