0
$\begingroup$

Could someone giver a clear and authoritative answer on HOW miles per gallon equivalent (or L/100 km) are calculated for battery electric vehicles like the Tesla Model 3 AWD long range?

On the Electric Vehicle Alberta website it states that a Tesla Model 3 AWD long range has a 1.8 L/100 km equivalent of mileage..But it shows the same value for all provinces...In reality this calculation will be affected by the particular mix to produce electricity in each province.

The Union of Concerned scientist has a more granular values for mileage for US states. Each US state/Region has a different estimate for MPGe.

https://www.ucsusa.org/sites/default/files/styles/original/public/2022-09/driving-cleaner-figure-2a.png?itok=jhyVduQa

How do you factor in the carbon intensity of an electric grid? Burning one gallon of gasoline releases 115,000 BTUs of heat the average amount of electric energy needed to generate 115,000 BTU is 33.7 kilowatt hour so if a vehicle travels 100 mi for 33.7 kilowatt hours it is said to have an effective mileage of 100 miles per gallon. I think the figure of 33.7 kilowatt hour is an average. In actuality you have to scale it by a factor related to how clean the grid is. In effect, in a cleaner grid you have to burn less gasoline to produce one kilowatt hour of electricity, and this affects the miles per gallon calculation..you essentially scale it by the carbon intensity of the grid.

Even in a hypothetical 100 percent clean grid, there is still the carbon emission in the manufacturing of the solar panels/windmills...In effect in a cleaner grid less gasoline has to be burned for 1 kWh of electricity in car. Is this reasoning correct? I think you a scaling factor/penalty needs to be added to account for how the electricity is produced in the grid in estimating MPGe.

What about the lifecycle of CO2 emissions of the electric vehicle and battery from manufacture to disposal? Is that also factored into miles per gallon calculations per US state or Canadian province..or is that lifecycle only used for CO2 emissions over the lifecycle, and only electricity generation is used for miles per gallon equivalent calculations per province?

Could you please illustrate with a simplified detailed hypothetical calculation for miles per gallon (or liters/100 km) equivalent two or three Canadian provinces..Like Manitoba, Alberta, and BC, or uses to show how differences in how electricity is produced in the region (mix of natural gas, coal, hydro, nuclear, solar...) can be accounted for different estimate of MPGe? Use the Tesla Model 3 AWD long range as reference.

$\endgroup$
4
  • 1
    $\begingroup$ One must use caution when attempting to incorporate the carbon penalty of producing the electricity in the calculations. One does not incorporate the carbon penalty of producing and transporting petroleum fuels while calculating fuel economy of a particular vehicle. $\endgroup$
    – fred_dot_u
    Commented Sep 2, 2023 at 23:06
  • $\begingroup$ In this Article it estimates Life cycle emissions of Both EVs and Gasoline vehicles..blog.ucsusa.org/dave-reichmuth/…. think what they mean here driving an electric vehicle in California produces the equivalent life cycle emission of driving a gasoline vehicle which gets 109 per gallon (obviously such a gasoline vehicle doesn't exist it's an abstraction). They consider life cycle emission for both the gasoline and the electric vehicle and scale accordingly. In Florida the number would be 73 miles per gallon... $\endgroup$ Commented Sep 3, 2023 at 2:52
  • $\begingroup$ This question has been cross posted on SE Sustainable Living. $\endgroup$
    – Fred
    Commented Sep 3, 2023 at 8:03
  • $\begingroup$ Won't mpg be affected by the driver and passenger mass? Which may be different based on continent - averages that is... $\endgroup$
    – Solar Mike
    Commented Oct 4, 2023 at 6:00

2 Answers 2

0
$\begingroup$

I think I found the answer to my question. I think what MPG estimates mean in this context is how many miles per gallon a hypothetical gas vehicle has to get in order to have the same life cycle emissions as an average Electric vehicle in that region. For example driving the average electric vehicle in California produces as much life cycle emission as would driving a hypothetical gasoline vehicle which gets 109 per gallon (obviously a gasoline vehicle that gets 109 MPG doesn't exist,it's an abstraction). They consider life cycle emission for both the gasoline and the electric vehicle and scale accordingly.

You can see why this would be different in different electricity regions in the United States because carbon emissions are different based the energy mix of the electricity grid.. for example in Florida driving an EV will produce a life cycle emission equivalent to driving a hypothetical gas car that gets 73 miles per gallon, and in upstate NY driving an EV this MPG estimate is 249 miles per gallon! Because the Electric grid in upstate New york is so clean our hypothetical gas vehicle has to go 249 miles per gallon to produce as little of a life time emission as the average EV emits there!

The Miles per Gallon estimate by the Union of Concerned Scientists study. is different from the traditional Energy equivalent view of MPGe..which is computed like this (33.7 kWH of electricity, and combusting 1 Gallon of Gasoline both produce 115000 BTU of heat). It is a matter of semantics, the emission based MPG estimate of an EV discussed here is not the same as MPGe that most people consider. Check out the two links.

https://blog.ucsusa.org/dave-reichmuth/todays-electric-vehicles-can-greatly-reduce-emissions-from-driving/

https://blog.ucsusa.org/wp-content/uploads/2023/03/EV-maps-2021-data_average.png

$\endgroup$
1
0
$\begingroup$

MPGe or Miles per Gallon equivalent. The energy contained in 1 US gallon of gasoline is about 130 Megajoules or is equivalent to 36 kWh (kilowatt hours) of electricity; however the thermodynamic and mechanical losses in energy converting chemical energy to mechanical horsepower averages 33-36 percent efficiency even less in bad driving/traffic.
An electric motor uses electricity solely and conversion losses are less severe but energy density of the battery is far inferior. If a Vehicle can travel 100 miles on 36 kWh of electricity, it would be rated with an MPG equivalency of 100 MPGe. But this is not based well.

Tesla' Cybertruck has a 123 kwh battery and routine testing reveal a range of 254 miles, less than promised in typical driving conditions (Albeit I suspect lead footers to be the culprit) In any case if true *Note there's 3.6 million joules or 3.6 Megajoules per kilowatt-hour 254 miles divided by 123 kwh is equivalent to 1.743 Megajoules per mile.

A gas car with a four cylinder engine say Chevy Cruze with 40 mpg uses 3.2 Megajoules per mile But note the motor enjoys a 80+ percent efficiency over the engine and energy density of gasoline is considerably higher than the battery.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.