I got home from a road trip on Saturday with zero miles of range left. I had to take another relatively long trip on Sunday so I needed to charge in range mode. I've got a separate meter for the Model S NEMA 14-50 so this seemed like a good opportunity to see exactly how much energy it takes to go from empty to full. Or almost empty, since zero miles showing doesn't equal zero battery capacity remaining. Anyway charging at 240 volts / 40 amps it took a little under 10 hours to charge and used 89 KwH. Not bad. I'm not sure how much is left in the battery at zero mils showing but I'm guessing that the 89 KwH consumed during charging translates to about 80 KwH in the battery. I was expecting more loss due to cooling etc.

Great post, thanks for the details. Makes me think single charger and 14-50 in the garage is going to be fine. 10 hours is plenty of time for an overnight charge. Looks like the worst-case scenario isn't so bad at all. Too bad California electric rates are so high: a full charge using 89kwh will cost me around $13. Still a screaming deal compared to gasoline.

is the Model S NEMA 14-50 model in fact an 80kWh battery? (confused about the rating of batteries by kWh....always thought they came measured in AmpHours).

Both Amp Hours and Watt Hours measure the same thing...battery capacity. But to compare Amp Hours assumes you know the voltage of the battery. So Amp Hours is useful for comparing batteries with identical voltage (i.e. all 12V batteries can be compared for capacity via AH ratings), but when comparing energy storage in electric cars, all of which use differing and unknown voltages, Watt Hours are the way to go. A Watt Hour is simply the Amp Hour rating multiplied by the Voltage, as Watts are calculated as Volts times Amps.

Well, EV-A/B is only around $0.10 per KWh, so it would cost about $9.00, but there is only 8-hours of off-peak per night... Wh is a way better unit of energy measurement. Ah doesn't tell you the amount of energy unless you know the voltage throughout the entire charge/discharge cycle.

My PG&E rate ( CA ) for solar ownership is off peak 18 hrs a day. Plus, the solar pays for itself eventually (6-8 years or so) and you never pay for power again. Unless you undersize your system. Also, I can't think of EVER doing a full charge. I have only pulled into my garage once with zero, and normally I charge from about 20%. Then I only charge to maybe 90%. So it only takes about seven hours. As if I care. I'm asleep, and I own solar. I'm waiting for Elon to get those storage batteries out.

I've been looking at solar for the last 5 years or so, but by all of my calculations, the ROI is still about 15-years. Problem is the biggest energy use is in charging the car (~700 kWh per month), and that is all done on off-peak $0.10/kWh. The home only uses about half that. When I get a second Tesla and add battery storage, that could definitely shorten the ROI, I think.