eMPG

[pwebb]

Hello. I am curious what eMPG folks are able to get. When I speak to my friends about it I tell them the EPA estimate is very vague as many variable are different based on where you live. The variables I use to calculate are as follows:

Cost of electricity. KWH. Very cheap in Loveland Colorado 6-7 cents kwh
Cost of gasoline. Per gallon $3.60
Efficiency of charging. This is where it's difficult to get accurate but I'm using a 80% efficiency
Actual KW of the battery that can be charged. 19.7 KW

Using these values and driving my 48 mile round trip commute which is 40% city and 60% highway the best I have achieved is 232 eMPG.

Any corrections in my math? What are you getting?

 

[WattsUp]

The EPA numbers rating of 105 MPGe is based on 320 wH/mi. I pretty consistently see 240-260 Wh/mi

The Wh/mile number from the EPA is based on "wall to wheels" energy (the energy that came out of the socket to charge the car and then drive it until the battery was depleted). In other words, this is the amount of energy that must actually be purchased in order to charge the car.

But, the Wh/mile numbers reported by the car are based on something related, but importantly different... the "battery to wheels" energy (the energy that came out of the battery to move the car). The car's numbers don't take into the "charging overhead", which is the energy lost between the wall and the battery during the charging process. Energy is lost because charging is not 100% efficient (it is only about 80% efficient). The loss is primarily waste heat, but this heating is something you must actually pay for in order to charge the car. It is the charging overhead.

In any case, you cannot directly compare the 320 Wh/mile from the EPA estimate with the Wh/mile numbers reported by the car. The car's measurements don't take into account the charging overhead, and will always be less (about 20% less) than the actual amount of energy you ultimately consumed (from the wall) to drive each mile.

But, good news... your FFE is delivering very close to (better even) the EPA estimate, since your average of 250 Wh/mile / 0.8 = ~312 Wh/mile. In other words, for every mile you drive around averaging 250 Wh/mile, you will need to buy 312 Wh of energy to charge your battery with that 250 Wh. The EPA estimated you would need to buy 320 Wh, so you're 8 Wh/mile ahead.

 

[hybridbear]

We've been averaging 213 Wh/mi according to the car which works out to 266 Wh/mi from a "wall to wheels" perspective like the EPA rating. I expect that in the winter we'll see our Wh/mi go to 275 or so which should put our year-round average near the EPA rating. This would mirror what I've experienced in all the conventional gas-only cars I've owned, worse than EPA MPG in winter, better than EPA MPG in summer.

 

[jmueller065]

I expect that in the winter we'll see our Wh/mi go to 275 or so which should put our year-round average near the EPA rating.

You'll be doing really good if you only get to 275 Wh/mi in winter--or we get a much milder winter than this past one!

Some relevant information:
http://jamiegeek.myevblog.com/2014/01/19/north-american-international-auto-show-naias-aka-the-detroit-auto-show/

and here, when it was relatively warm (20-30F) I was getting 270:
http://jamiegeek.myevblog.com/2013/12/09/the-weather-outside-is-frightful/

 

[hybridbear]

I expect that in the winter we'll see our Wh/mi go to 275 or so which should put our year-round average near the EPA rating.

You'll be doing really good if you only get to 275 Wh/mi in winter--or we get a much milder winter than this past one!

Some relevant information:
http://jamiegeek.myevblog.com/2014/01/19/north-american-international-auto-show-naias-aka-the-detroit-auto-show/

and here, when it was relatively warm (20-30F) I was getting 270:
http://jamiegeek.myevblog.com/2013/12/09/the-weather-outside-is-frightful/

Well, we park underground so our car will always start out warm in the winter in the morning which should help. We normally would never need to turn on heat on the first trip leaving home of the day in the car since we park in a heated garage.

 

[jmueller065]

Well, we park underground so our car will always start out warm in the winter in the morning which should help. We normally would never need to turn on heat on the first trip leaving home of the day in the car since we park in a heated garage.

Up until Mid-Feb my car was outside and plugged in (preconditioning outside). After Mid-Feb it is inside an attached garaged (e.g. semi-heated). I don't think either matters if you use the go times: when getting in the car outside it was just as toasty warm as it was sitting in the garage. The only difference was reflected on the power meter (took a lot more juice to precondition the car when it was sitting outside in -10F vs a 40F garage).

Our weather last winter didn't really break until late March or even mid April (sheesh) so even after Feb it still was driving in the snow, sloshy, yuk at <0F.

On those days my car would start out at 85F. A few miles in I'd either have to open the windows, or run the defroster to clear the frost accumulating--even if the car is warm you are still in it breathing, exhaling moisture which will accumulate on the cold windows. I found that if I leave the car on defrost set to "LO" from the start it would keep the windows clear during my 15 mile commute but I'd be mighty cold when I arrived at work. On the really cold days I found myself cycling the defroster set at 60F or 65F.

On the really cold days, if I set the temp to 65F or so and just let it work I would return home right at the 10 mile to go warning (for a total effective battery range of 40 miles).

 

[dmen]

1. MPGe = mi/kWh * kWh/gal of gas. EPA says there are 33.7 kWh of energy in a gallon of gasoline.
So: take your car's Wh/mi
make it kWh/mi
divide it by 0.8 for estimated charging efficiency to get energy from outlet used per mile
Divide 1 by that number to get mi/kWh
Multiply that by 33.7 to get MPGe

2. Hybridbear, it's really hard to guess how energy efficient your car will be in winter. Good news is that in your heated garage you won't be using electricity to preheat the battery/cabin much. That energy use is not often included in people's tallying of "fuel cost" and won't show up in your car's Wh/mi even if remote started off plug, but it isn't negligible. Nonetheless snow, fogged or iced windows, inactivated or reduced regen when starting off a drive in a frigid cold car, and heavier traffic making drive times longer and therefore cabin heating less optional can all reduce your efficiency to a surprising extent. Considering MN is quite a bit furher north than Chicago where I drive, I will be in awe if you can keep it to 275 Wh/mi.