The following is a fun graph I recently ran across on Wikipedia. It shows the completely explosive solar power growth that has occurred in California, Arizona, New Jersey, Nevada, and New Mexico since 2010. Different factors have been at play here. For one, the price of solar panels has come down dramatically. In some of these markets, 3rd-party solar that lets people go solar for $0 down or close to $0 down has been important. In California, it accounts for about 70–80% of the residential solar market. The SREC market in New Jersey has been big for stimulating growth there. No matter how you look at it, though, this is awesome:
Note that the data are for the years 2009–2012. Solar power leapt to new heights in 2013.
Image Credit: Plazak (CC BY-SA 3.0 license)