I haven't seen this posted before, so I apologize if I'm reposting.
Mostly for people with SDGE/PGEC in Southern California, but I think very helpful for anyone.
This calculator lets your download your electric company's 'Green Button' data and see how adding an EV (including the Model S, and including your mileage and style of driving) or adding solar will affect your electricity use and bill. It even shows you how various electricity rate plans from these two utilities will affect your bill.
I think it's been pretty darn helpful.
Disclaimer: I have no ties to this company whatsoever.
http://www.greenbutton.
ecodoginc.com/GBCApp/
edit: I don't know how to make the link work, you have to copy it into your browser