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Old 08-29-2019, 03:59 PM   #1
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How to input EV fillups

I've started inputting "fillups" for my Tesla Model 3 and noticed that the way other Model 3 owners are inputting fillups is resulting in incorrect MPG numbers (way too low). Fuelly requires miles, gallons, and cost as inputs. This is the way inputs should be calculated for correct EV efficiency (MPGe) calculations:
  • Miles is straight from your vehicles trip meter.
  • eGallons is (Wh/mi)*(miles)/33700. This is easy if your EV displays consumption in average Wh/mi and miles driven in your trip meter.
  • Cost is (Wh/mi)*(miles)*($/kWh)/1000. Where Wh/mi is from in vehicle trip meter, miles is from in vehicle trip meter and $/kWh is your utility or charging station cost per kiliowatt hour.

With these inputs fuelly can correctly calculate MPGe for an EV and you will find it is the right order of magnitude to compare with other EPA numbers.
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Old 08-29-2019, 07:26 PM   #2
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What is correct MPG or MPK (Miles per kilowatt)?

I too started to put in my numbers as MPGe but saw most were ending up with MPK. My reason for changing my numbers was to match what most others were doing so as to have a consistent format.

It could be argued that I don't put any gas in so the gallons heading is wrong, so how do we work with the format given. It is much simpler to just put in kWh used as gallons and no other figuring outside the app has to be done. The resulting number is Miles per kW an accepted number for many. I would rather see watts per mile or kW per 100 miles but that too will probably not happen.

Adding to the argument that we don't put gas in the car, a number of 33.7 kW per gallon can also be misleading. If for instance you live in a state that has mostly hydroelectric power. There are no hydrocarbons in making the electricity.

So it might be more accurate to say we get 3.8 miles per kilowatt than trying to convert it to 130 MPGe. There is also the charging efficiency factor so this would add an additional calculation. I would like to stick with gallons equal kW and we understand it will give us MPK. I can use the watt meter on my EVSE so the efficiency is in that kW number.
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Old 10-11-2019, 11:15 AM   #3
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Perhaps 5% of my fill-ups are commercial or locations that are not my house. At my house, my solar array provides all my electricity, so the cost is 0.

Is there really a need for Fuelly in this case? Are others still using the services?
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Old 10-11-2019, 12:06 PM   #4
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Quote:
Originally Posted by DaVolt View Post
It could be argued that I don't put any gas in so the gallons heading is wrong, so how do we work with the format given. It is much simpler to just put in kWh used as gallons and no other figuring outside the app has to be done. The resulting number is Miles per kW an accepted number for many. I would rather see watts per mile or kW per 100 miles but that too will probably not happen.
Along with, and in smaller print, MPGe, the EPA reports an electric car's efficiency in kW/100mi. In the Fuelly profile settings, you can choose G/100mi for your display.

Quote:
Adding to the argument that we don't put gas in the car, a number of 33.7 kW per gallon can also be misleading. If for instance you live in a state that has mostly hydroelectric power. There are no hydrocarbons in making the electricity.
The unit is actually kWh. Watt-hours are a unit of energy, and is independent of the energy type and source. We don't use different units for electricity made from different sources.

The actual energy content of a gallon of gasoline varies with the component blends. 33.7kWh per gallon is the value the EPA chose to use for MPGe calculations.
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