I would bet that when you run the actual numbers, you'll find that using peltier chips actually reduces your gas mileage as the load on the alternator increases.
I'll take that bet for any amount you want to part with.
Alternator loading on vehicles is much less than AC compressor loading (and alternator loading on newer cars supplemental electric cooling)
You may be right. The alternator just may simply sieze up when the cooling system draws 100 kilowatts.