Context: I sell cars and currently have a Nissan Leaf. A customer had asked if I knew why it had 121city/91highway MPG listed if it was a fully electric vehicle. This confused me too and it’s apparently a common thing? Thanks.
In: 7
It’s an equivalence thing so you can compare the efficiency of ICE, BEV and PHEV vehicles.
They just compare energy consumption and convert it to if that energy was from gasoline.
How else are you going to compare the efficiency to an ICE vehicle?
Its a measure of efficiency to allow people to compare the energy consumption, they’re rated in MPGe (Miles Per Gallon equivalent)
Why list it as Miles per Gallon instead of kWh/mile or miles/kWh? Because they did some surveying and determined people don’t know what a kWh means in terms of their car and found MPG less confusing and consistent with the existing markings
121/91 MPGe city means the Leaf used 0.278 kWh/mile on the city driving test and 0.370 kWh/mile on the highway test
It doesn’t directly compare to the costs/CO2 emissions of a gasoline powered vehicle because it doesn’t deal with the upstream power generator efficiency but its a start and allows for comparisons of efficiency between electric cars beyond just the stated range which is heavily influenced by overall battery capacity
It’s a way to easily compare vehicle efficiency. Personally, I used $/mi to compare my leaf’s operational costs and the ice vehicle it replaced. I think Nissan’s marketing called it eMiles at the time.
I’m glad you asked this question, I didn’t know there was a rating, and this is super interesting to me. I had no idea that EVs were that much more efficient at converting energy, and had assumed that the benefits were something of a wash if their supporting powergrid was using coal or petroleum to generate the electricity to charge the car.
Doing a little research, it looks like the range of efficiency is 120 MPGe for a Tesla Model 3 (the best), and 68 MPGe for a Ford F-150 Lightning (the worst).
That tells me that the absolute worst electron guzzlers are still better than the absolute best internal combustion vehicles (Hundai Ioniq at 59 MPG for 2022).
Obviously there are additional environmental concerns with the original manufacture of electric vehicles, especially in coal burning countries like China, but if your electric grid is backed up by wind, solar, or hydro, this seems like a cowabunga slam-dunk.
Am I forgetting something, like power lost in transmission through a grid?
It’s MPGe (miles per gallon equivalent), and it was invented so that consumers could (sort of) compare the efficiency of electric cars and non-electric cars. Unfortunately, it’s not intuitive in any way.
The US Environmental Protection Agency determined that 33.7 kWh of electricity was equivalent to 1 gallon of gas. So, if a car goes 4 miles on 1 kWh of electricity, that’s equivalent to 33.7 x 4 = 134.8 MPGe
The 33.7 kWh per gallon assumes 100% efficiency in conversion of the chemical energy of combustion in a gallon of gas into mechanical energy. However, a typical internal combustion engine is typically about 25% efficient (and electric motors close to 98%). As a result, it’s a pretty dubious way to compare EVs and non-EVs. It’s an OK way to compare EV to EV, though miles per kWh is more meaningful because it can be easily used to estimate the cost of operating the car.
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