Said only it's a source which CAn't be replenished in a pace equal-to or more than it's used. On the other-hand, if we could produce automobiles that run 100 we'd be employing a renewable source - sunlight. These fossil fuels basically supply the vitality that pushes the U.S's economy. Because the sunshine provides so much vitality that we would be in no threat of depleting it it would be alternative.
About the other hand, if we could actually generate cars that function 100% on solar energy, we'd be utilizing a green resource - the sun. the electricity that pushes the economy of the U.S is essentially provided by these fuels. It would be alternative since the sunlight provides so much electricity that we wouldbe of depleting it, in no risk.