from discussion here I got the feeling that at a given minimum size, the answer is : Rankine Cycle turbine, maybe Organic Rankine. however the minimum size is not clear... maybe car (20-50kW) is possible. have to work on turbine, but also radiators, key problem.
for CHP 7-15KW, not sure it can be efficient, but it works. for smaller power, or smaller vehicle (motor bikes, moped, bike assist)... maybe no good solution. stirling or turbines are too heavy, have low efficiency. thermoelectric devices have bad efficiency for bikeassist less that 100W mecanic , with a battery, in serial hybrid configuration, could do the job (to refill in the day/night, and push on slope about 200-500W). miniaturization will be more important than efficiency. for moped you can get 1-2kW... for motorbike it can start from few 5kW to above 50kW, but won't be fun over 10-20kW unlike today 2012/2/8 Guenter Wildgruber <gwildgru...@ymail.com> > The next billion dollar question: How to get electricity from say 400°C > with minimal cost/maximum efficiency? >
