The following has directions for getting the numbers from PG&E.

In order to suggest appropriate sizes for a photovoltaic system or solar thermal system and do an analysis, it is helpful to know your current or projected electrical consumption in terms of kilowatt-hours per month, and your natural gas consumption in terms of therms per month.

From the consumption I can tell you the economics of different options (replacing all your usage with solar, replacing some, ...).  Because of the structure of the rates, the economics are very dependent on your consumption.  The same size system can save different amounts for different people.