Forbes has a whole feature on Solar Energy this week. Within, I found a chart that I have been seeking for a long time - a chart tracking the declining cost of electricity generated by photovoltaic surfaces.
It appears that cost parity with present residential electricity rates is finally imminent. Also, migration to solar power could happen rapidly before full cost parity due to tax breaks, and the fact that solar energy is generated at the time of day when electricity rates are already the highest.
For reference, below is a chart of US solar intensity. It is quite possible that by 2020, many homes in the southern US will have photovoltaic surfaces on their rooftops. This, combined with the spread of plug-in hybrids and fully electric vehicles (including those from Tesla motors, which come with their own included solar panel), will lead to a fascinating simultaneous shift from a portion of coal consumption to renewables (solar, wind), and from a portion of petroleum consumption to electricity. So solar would indirectly eat into a small slice of oil consumption.