Rooftop solar (more generally, "distributed generation") is growing rapidly and is expected to be a much larger electricity source than utility scale photovoltaic plants fairly soon, say by 2020 or even earlier.

The following link shows solar utility and DG through 2014. Sorry, can't immediately find the predicted values through 2020.

http://seekingalpha.com/article/3085476-the-long-term-prospe...