Measuring electric vehicle efficiency: What is MPGe?
Electric vehicles offer large cost savings over traditional gasoline-burning vehicles. That’s simply because electric vehicles use electricity as fuel instead of gasoline. Electricity is much cheaper than gasoline, making it much cheaper to recharge a car than to refill a car.
A lesser-known fact contributing to the low cost of driving an electric vehicle is their efficient use of energy. That is, how much energy makes it to the wheels versus being lost as wasted heat.
Most internal combustion engines operate at less than 40 percent thermal efficiency. That means that less than 40 percent of the energy in each gallon of gasoline is actually used to turn the wheels while the rest is wasted in the form of heat. Meanwhile, electric motors can be more than 90 percent efficient. Nearly all of the electricity onboard is going to the wheels with very little being lost as heat.
There’s an easy way to illustrate what this means. One gallon of gasoline contains approximately 33.7 kWh of energy. The 100 kWh battery pack in a Tesla Model S 100D contains the energy equivalent of less than 3 gallons of gasoline.
While a 2019 BMW 530i (24 mpg city/34 highway) could only go 72–102 miles with that same amount energy stored in gasoline, the Tesla Model S 100D will travel more than 300 miles—because so much of that energy is being used to drive the car instead of being wasted as heat.
MPGe (Miles per Gallon equivalent)
MPGe is the official metric that the Environmental Protection Agency uses to measure the efficiency of alternative-fuel (including electric) vehicles. This makes it the most common measurement you’ll come across when researching an electric vehicle.
Just like regular MPG shows how far a car will travel on one gallon of gas, MPGe shows how far a vehicle will drive on 33.7 kWh of electricity—the energy equivalent of one gallon of gasoline.
For Example
The aforementioned Tesla Model S 100D is rated at 102 MPGe, and numbers can fluctuate from lower to higher, like the 2019 Jaguar I-Pace’s 76 MPGe, or the 2019 Hyundai Ioniq EV’s 136 MPGe.
These efficiency differences can be expected because the I-Pace is a large and powerful all-wheel drive crossover while the Hyundai Ioniq EV is an economical front-wheel drive car.
Keep in mind that a very efficient vehicle with a high MPGe rating does not necessarily mean that the vehicle will have a longer range—that depends on the battery size.
The I-Pace has a mighty 90 kWh battery pack compared to the Ioniq EV’s modest 28 kWh pack. No surprise – the Jaguar will go 234 miles on a full charge while the Hyundai will go 124 miles.
But a Tesla Model S 90D, also sporting a 90 kWh battery, will run 294 miles on a full charge – further than the Jag. Why? Because the Model S is rated at 95 MPGe, meaning it uses its electricity more efficiently than the 76 MPGe I-Pace.
When looking for an electric vehicle, it’s important to consider both MPGe and range. A more efficient vehicle will cost you less to recharge, but you need to make sure you’ve got enough range to get through.
Where can I find this information?
The EPA maintains a website, https://www.fueleconomy.gov, where you can look up fuel efficiency and range numbers for any vehicle sold in the United States. You can even bring up multiple cars at one time for easy comparison, making it easy to get an idea just how much you can save by switching to electric. When you’re ready to plug in and get Current, range is prominently displayed for every vehicle in our inventory.
Image credit: fueleconomy.gov | Check out the efficiency of the cars mentioned in this article yourself!
3 comment(s) so far on Measuring electric vehicle efficiency: What is MPGe?
I had figured it was a way to make equivalent comparisons using the legacy conception we’re all used to.
I wonder if we’ll still refer to “miles per gallon” long after EVs have taken over – after all, we still rate automobiles in “horsepower” 🙂
It’s an important thing we need to figure out! MPGe makes comparing easy, but it isn’t especially useful beyond that. It would be nice to see something like watt hours per mile become the standard at some point for EVs, it’s just more relevant.
It is amazing that the EPA has come up with a measuring unit MPGe that is based on converting an invariant unit to some arbitrary equivalent based on “equivalence” of energy when EV efficiency vs. energy consumption IS NOT CONSTANT. It is totally incorrect and misleading. The numbers of EV efficiency on the EPA “stick-on” label are wrong and misleading gotten by “receptacle-to-wheels” method. It is ignored that 79% of electric generation in US generated by fossil fuel and CO2 with other greenhouse gasses are emitted true the Power Plant chimney. Only “well-to-wheels” method will evaluate efficiency and emissions of energy complete and accurate. Additional QR code on the stick-on car label can be added and used for “well-to-wheels” method to evaluate efficiency of the EV at the location where QR code is scanned. Locations may be divided by States and Provinces.