in the absence of a major change in battery technology(cos in terms of weight/range etc we are still at a similar level to the 19th century)then long term usage is likely to be hydrogen fuel cells or similar although the power rqmnts for generating hydrogen are gonna require in all likelihood summat along the lines of workable fusion power.that is at least possible,look at the sky with that bright glowy object for a simple confirmation!hydrocarbons are a limited resource and grow ever rarer and bio fuels will require agriculture on a scale thats likely to impact food production so i dont see that ever being more than a niche but keep in mind some countries are and will be banning i c vehicles in the near future
