I just finished calculating an estimate based on my circumstances. I drive 210 miles per week, nearly all of it is an urban work commute. I tend to stay off the highways and opt for surface streets, so I'm expecting to see 3.5 miles/kWh or more.
I'll charge daily in my garage during off-peak hours. My rate plan is 12.6 cents June through September, and 8.5 cents October through May. So that's 3,570 miles in the summer, divided by 3.5 miles/kWh, times 12.6 cents, for a summer time cost of $128.52.
Winter is way better! 7,350 miles, divided by 3.5 miles/kWh, times 8.5 cents, for a winter cost of $178.50.
That’s $307.02 annually. My current 2011 Clubman gets right at 30 MPG. I can fill up at Costco for $3.15 a gallon. making the same annual mileage cost $1,146.60. So even at just under 11,000 miles, I ought to be able to save $840 a year.
This assumes gas prices will stay above $3…a pretty safe assumption I think. If I were to switch to the “Overnight Savers” plan on my electric service, assuming I could keep my daytime usage low enough for it, that would change my 12.6 and 8.5 cent rates to 6.1 and 5.2 cents respectively. That would bring my savings awfully close to $1,000 a year.