Model S:
"Fuel" efficiency and cost
To cover 15,243 miles, I used 5,074 kWh of electricity, for an average of 333 watt-hours per mile. That's a bit better than the car's EPA-rated efficiency of 350 Wh/mi, and converts to precisely 3 miles per kWh.
I used about 1,275 kWh of free Supercharger power on three long road trips totaling about 4,000 miles. So about 3,800 kWh of the 5,074-kWh total came through my electric meter.At my local utility's rate of 14 cents/kWh, that works out to a total fuel cost for the year of $530, or about 3.4 cents/mile. Contrast that to about $3,000 and 20 cents/mile for a comparable car like the Mercedes S Class.
But the Model S actually used more electricity than the 5,074 kWh on the car's energy meter.
For one thing, the charging process is only about 85 percent efficient. Which means that for every 85 kWh used by the car, 100 kWh came through my electric meter. In reality, that 5,074-kWh number is actually more like 5,700 kWh.
In addition, my car's "vampire" power draw while parked and shut down averaged about 4.5 kWh per day for the first 10 months, and then about 1 kWh per day after a software update two months ago. I estimate the vampire draw sucked up an additional 1,400 kWh or so.
That brings total actual energy usage for the year: about 7,100 kWh--putting efficiency at about 466 Wh/mile, or about 2.1 miles/kWh.
The vampire and charging losses bumped the year's real fuel cost up to $820, or about 5.3 cents per mile. Which is still barely a quarter of the fuel cost of a comparable gasoline car.