Model S Equivalent Mile Per Gallon closer to 60 EMPG

Model S Equivalent Mile Per Gallon closer to 60 EMPG

I noticed that my model S was "leaking" range every day it sat unplugged so I decided to get a real idea of the effect of this on E-MPG. I also wanted to know exactly what I was paying for the car per mile so i installed a household watt hour meter like the one on the side of the house right before the wires go into the charger. I have tracked the KWH usage by the charger over the past 6 weeks or so and have come up with 351kw took the car 687 miles. This yields an efficiency of 511wh/mile. at 4.00/gallon and .14/kwh this period yielded 56mpg equivalent. which is a lot different than the 89 empg that the epa rated this car at. The car seems to us 3kwh per day just sitting there. Over the 28 day period i checked this that would account for 84 kmh of the 351. if you take that out the efficiency would have been 388wh/mile or 74empg (getting closer). and i am told that chargers are 90% efficient or so? (correct me on this if someone knows the actual on a 220v 40amp plug) So if the charger were 100% efficient and they could find a way to fix the daily leak the car would have done 350wh/mile which is a lot closer to the 325wh/mile the screen claims in the trip log over the same period.

So leaving the computers on is robbing me of 18mpg.

DouglasR | 8 avril 2013

I don't know of any utility that imposes a separate transmission charge on residential users. Taxes are something else.

village33 | 8 avril 2013

@Mark E, I agree with you and I live in the US. There is nothing confusing about an electric bill, every bill shows X power delivered and Y $ total cost. A monkey could read it. There is a breakdown of sub charges (in CT including production, taxes, surcharges, transmission, etc) but only the total cost per kWh matters. In CT I can choose my producer and production vs transmission is about 50/50. My total cost is $0.13/kWh. For those who care in CT it is 50/50 nuclear/nat gas (green/clean).

@DouglasR, in CT there is a production section per kWh and transmission section per kWh. This is necessary since we can pick both producer and price lock period (floating, 6mo lock, 12mo lock, etc).

Nothing complicated about either, but it does vary by state and within a state by utility.

gasnomo | 8 avril 2013

just for the record, my 11.5 cents/kwh is total cost, that includes NYSEG and supplier costs which breaks down 5.5 cents and 6 cents respectively...same figure as when i take my total bills for the last 12 months divided by total usage...

gagliardilou | 8 avril 2013

I asked Tesla service if the total kwh used included the vampire drain and he said yes. By the total kwh used shown in the car, I am getting 90 miles per gallon equivalent at $4.00 a gallon for gas and paying 11 cents per kwh. I drive alot and believe I am saving a lot of money everyday compared to my BMW.

DouglasR | 8 avril 2013

@village33 - I stand corrected. I used to follow this stuff pretty closely, but it looks like things have changed since then.

@lgagliardi - I'm not sure what you mean by "total kwh used," but if you are referring to the kWh figures in the trip meters, they measure consumption only when the car is moving. Just look at the total kWh used "since last charge." Charge your car, then unplug it for a few hours. You will see the Rated Miles decrease even though kWh used since last charge stays at 0.

kjo | 8 avril 2013

@DouglasR - we pay a certain amount for production and another set rate for transmission. We are in a deregulated TX market. Transmission is is fixed price set by the line utility, the production cost is the one that has price competition by producer. This is for residential and commercial.

Brian H | 8 avril 2013

If each car does 10K in a year, and is written down to 50% in 3 yrs, that's
$100K for the S350 + (25 mpg) 400x$10=$104,000 for 3 yrs or $3.34/mi.

$43.4K + (13+9)/2=$.11/kWhx2.5x300=$82.50= $43,582.50 or $1.45/mi.

So the S350 is 2.3x as expensive.

The above assumed 400Wh/mi, for difficult and aggressive driving.

Brian H | 8 avril 2013

Note that comparative fuel costs are $4,000 vs $82.50.

jackhub | 10 avril 2013

Reading this thread reveals one thing for sure. Electric utility rates in the US vary all over the place- not just the level but the structure, too. I pay an off peak rate of 0.06089/Kwh including everything. Bottom line. At an average of 330wh/mile and $3.75/Gal of gasoline, I am getting about 187 EMPG with no vampire effect. If I assume 10% loss for the tooth fairy, I am still getting over 168 EMPG. I behaved myself this past week and got 300wh/mile. So this past week I got 185 EMPG including the tooth fairy. Still not bad.

gagliardilou | 10 avril 2013


I thought the service guy was wrong. I am getting a separate meter installed for the car under the utility company NIPSCO ev program. I will get free charging till jan of 2013. Then I will know exactly what the car is using. Regardless what it is, I really enjoy the car and not going to the gas station!

DouglasR | 10 avril 2013

There are two kinds of energy consumption that don't get counted by the kWh counter on the trip meter. First, there is the vampire load when the car is not moving: electronics, battery heating/cooling, etc. Second, there is the energy consumed as a result of charging inefficiencies: the difference between the number of kWh that the car thinks its getting and the number of kWh that your utility is selling (and billing you for).

Like others, I love the car and don't worry about it.

Brian H | 11 avril 2013

You will be charging in the past? How will that work? I thought only Flux Capacitors could pull that off.


tommy-tesla | 11 avril 2013

@DouglasR: Sorry, but that's simply not correct. The vampire loads, etc are all accounted for. This has been confirmed multiple times.

You are correct however about the loss due to charging inefficiencies.
I assume it's less than 10% (90+% efficient DC converters are not uncommon). Worth mentioning: Tesla has stated that charging at less than the maximum is less efficient.

DouglasR | 11 avril 2013

@tommy-tesla - Are you saying that the trip meter records the vampire loss while the car is stationary? Because I think that's wrong. Unplug your car and let it sit overnight. Then look at kWh consumption on the trip meter. It will show 0 kWh used since the last charge.

I do believe, however, that the vampire load is accounted for on the trip meter when the car is moving.

tommy-tesla | 11 avril 2013

@DouglasR try driving the car after it having sat all night. If I'm right, the consumption will jump up. Normally I don't see it because I charge every night. I'm pretty sure I've casually observed it, but I'll make a point to test my claim tonight.

DouglasR | 11 avril 2013

For me, the car's consumption behavior starting out is the same whether it has been sitting all night or just finished charging. Run the heater on a stationary car, and see whether the trim meter records the usage.

tommy-tesla | 12 avril 2013

My understanding was that the tally isn't updated without the car moving.

When I parked:
Since Last Charge: 46.9 mi 15.3 kWh avg 327 Wh/mi
Rated Range: 176 mi

After ~ 12 hours:
Since Last Charge: 46.9 mi 15.3 kWh avg 327 Wh/mi
Rated Range: 171 rated range

Thus the loss of approximately 5 * 300 = 1500 Wh isn't in the
trip counter

Add 0.2 mi of very slow driving (downhill):
Since Last Charge: 47.1 mi 15.4 kWh avg 326 Wh/mi

So it looks like I was wrong, but I need a bigger vampire drain
to be completely sure.

DTsea | 13 avril 2013

electron, i dont really care how they calculate mpge on the sticker, but i do care about fuel cost per mile and my calculations are valid, call it something else if you want.

brian h, i drive the same amount but i like it a LOT MORE!

djp | 13 avril 2013

My 60 is consuming 200w per hour keeping the vampire alive, 24 hours per day stationary or moving. $.34/kWhr = $599 per year. Not a large amount of money, but a complete waste. Need to leave a car at the airport while we go on a 3 week vacation. Disappointed we can't take the MS...have been spoiled for 2 years with our LEAF; guess we'll take it to the airport.

Certainly hope someone at TM is working on this.

Brian H | 13 avril 2013

No taking the long way to work? No running extra errands as an excuse to drive? No Sunday joy rides?

kenheidorn | 26 avril 2013

1123.7 miles, 336.4 kWh this works out to 112 eMPG. This is my real world consumption for the last month.

Of course this does not include the electricity used to keep the car in standby mode. It also does not include the electricity to open and close my garage door.

I guess you can calculate the consumption all sorts of different ways.

This car is awesome!! It makes my diesel Jetta seem like a fuel hog.

RedShift | 26 avril 2013

My consumption is a bit lower at 310 kwh average. (60kwh car)

I don't care what the equivalent eMPG is, I just enjoy driving my car.