[mhandley]

But nothing in the real world really follows an exponential. In reality, what looks exponential is almost always a logistic curve: http://en.wikipedia.org/wiki/Logistic_function

I'm optimistic about solar too, but even if it looks exponential now, this doesn't tell you much about where it will level off. That will no doubt be determined by how cheap the panels become, and how cost effective storage technologies turn out to be.