CA has two basic rate structures: Time of Use and Tiered. Tiered doesn't care about when you use power but cares how much. The more you use per month, the higher the rates.
For PG&E (SF Bay Area primary provider), the current rates for standard Tiered Residential (E1) start at about 13 cents per kWh and go up from there. Once your usage hits 1.31x the "baseline" allotment, you're paying about 28 cents per kWh. That goes up to about 33 cents per kWh once you hit 2x the baseline allotment. PG&E adjusts the precise rates all the time. They've had 3 rate schedules for 2012 and the year's not over yet.
Peak rates for Time-of-Use (E9A) are 30 cents per kWh during summer and 9 cents during winter. Rates drop to about 4 and 5 cents during off-peak for summer/winter.
The upshot for the SF Bay Area is that you win if buy enough solar that PG&E is crediting you for power but you still owe PG&E some money. The win goes down if you don't buy enough solar or you buy so much so that PG&E pays you. Because when they pay you, they pay wholesale supplier rates, not retail rates and the wholesale rate isn't enough to cover the cost of generating that power from solar panels.
Details follow:
If you generate less power than you use, CA requires that you get credit for the generated power at retail rates. So if you're on a Time-of-Use plan and at 2 pm, power costs 30 cents per KWH, if your meter is running backwards at 2 pm, you get credited 30 cents per KWH that you generate. It's simpler if you're on the standard tiered residential plan: they just add up your usage, subtract out the power you generated and you pay standard rates for what's left over.
In both cases, if you generate more power than you consumed over your one year true-up period, the power company (or at least PG&E) pays you wholesale rates, not retail rates for the surplus. I think that's currently about 4 cents per kWh.
So if you want to maximize your ROI for this part of CA, you need to look at your current and projected usage patterns and then get the right amount of power and put yourself on the right rate structure. Time-of-use works really well for people who can avoid using lots of power during peak hours. They get more credit in the summer for their power produced and pay less for power consumed. If you've got kids so you're running the AC a lot during the hot months, staying with the standard rates may be a win.
If you guess wrong and you don't buy enough solar, you'll be paying for power at peak rates or at 3x baseline prices depending on your plan. If you guess wrong and buy too much solar, PG&E will pay you money but almost certainly less money per kWh than it cost to put the panels in. Even with the best SolarCity plan, the cost of solar power is 9.9 cents per kWh for me. So if I buy too much solar, I lose 5 cents per kWh for every kWh that PG&E pays me.