As more rooftop solar (residential and commercial) is deployed in California (the leading state for distributed solar capacity, by far), the impacts are being seen on the grid.
The solar generation hours (between 7am and 7pm in March) are showing a marked decline in load profile. Here is a typical example, from Thursday March 27, 2014 compared to Thursday, March 28, 2013. The difference in peak load is only about 300 MW, but the daytime difference peaks about 3pm at 1,500 MW.
It does not require an advanced degree to see where this is going, nor to see what the impact on peak load would be if battery storage rolls out in sufficient quantity to store some solar power for about 5 to 6 hours (economically).