I also remember (not on this thread) someone saying that it wasn't worth it because you needed to get a deep cycle battery that could be discharged and recharged and it only had a certain life span. the replacement cost would all but negate any MPG gains you saw from the process.
there again, can't remember where I saw that so I can't say either way if it is true. just remember it from a while back. I drive too far for it to be practical for me either way. 40 miles on my short days 100+ on my long ones. sometimes at night for both cases.
Be the change you wish to see in the world
Has anyone actually tried thermoelectrics as a replacement for alternator power? It seems like this would be HUGELY more practical than solar panels. In fact, this is actually something the automakers are looking into as a way to increase fuel economy. And, given the HUGE amount of availble heat in the exhaust, the relatively low efficiency of current thermoelectric generators is not a problem. Anyway, I have seen the modules available relatively cheaply various places online (although I don't know how heat tolerant they are). So it looks like this might be something to look into.