I remember reading one of Smokey Yunick's cars resulted in a rule change in nascar (well many of them did, I'm sure, but I'm thinking of this specific one) was where he disabled the generator (I think it was a generator, not an alternator, but that's really of no consquence) in the original spot, and fitted one somewhere (possibly just below the bumper, but still inside the engine bay, but don't 100% take that location to the bank) else with an appropriately bladed propeller attatched to the front. At the speeds they were doing, it was more than enough to keep the battery charged. You'd probably be doing half the speed on average, so would need to use blade pitch to suit, but it might be worth a look. You could even have a manual switch that cuts out the std alternator for the economy run, but cuts back in for stop start traffic and the like.