Okay before you flame me for using hydrocarbons .. this is just an "out of interest" thing. A 10KwH generator consumes around 1.2 gallons of diesel per hour. 10KwH will add 28 miles to your Tesla in an hour. So even with this hyper-inefficient setup (double energy conversion), you're still looking at 23mpg. Not bad for a car of this size and weight. Not bad!