It is actually even more insane then that. We know how to built electricity grids. The US is a large country, so it is pretty much a given, that it is windy somewhere in the US. Somewhat similar story with solar as well, but of cause nights cause a bit of a problem. The storage needed to run a well connected grid is fairly low. More so the US has a lot of hydro. The water reservoir can be used as a form of power storage, by changing how much water is let out. Obviously there are limits to that, but the potential is massive.