What is going to replace oil. It already been shown the wind and solar can augment oil, but can't replace it, so don't go there. Hydrogen has never lived up to the hype, and nuclear only has the potential for large scale industrial use. There is no doubt that at some point in the distance future, an alternative inexpensive fuel for mass consumption will be discovered, but it is likely all those grandchildren that you talk about will be long dead when that happens.