I have a lightning and it averages 0.5kwh/mile and my electricity price is $0.15/kwh, so it costs me $0.075/mile to drive. At current gas prices that's pretty much the same as a very efficient hybrid compact car (55mpg @ ~$4/gallon). If I had solar I could probably offset almost all of the lightning fuel cost based on where I live (sunny) but it's so cheap it's not worth it.

Do you mean "much more efficient" in places where electricity rates are significantly higher than the national average? Or only much more efficient when compared to when you're charging at charging stations?