How The EPA Rates Electric Cars: Range, Efficiency & More

Model 3 EPA range and MPGe numbers

DEC 2 2018 BY JIM GORZELANY 27

IT’S ALL ABOUT RANGE, KWH/100 MI, AND MPGE.

As with conventionally powered models, electric vehicles are rated for their energy efficiency – and in this case their operating range on a charge – by the Environmental Protection Agency. If you’re already an EV owner, you probably have noticed that your power consumption and/or range doesn’t always jibe with its official ratings. As automakers usually say in ads that reference a vehicle’s fuel economy, “your mileage may vary.”

A big reason for this is the manner in which vehicles are tested. Contrary to what you might expect, they’re not driven on the open road. Rather, a vehicle’s energy consumption is determined in a laboratory using a standardized procedure that’s mandated by federal law.

TEST PROCEDURES

Each vehicle tested is “driven” on a device called a dynamometer. Think of it as a treadmill for cars. While the engine and transmission drive the wheels, the vehicle never moves, just the rollers upon which the wheels are placed.

A professional driver runs the vehicle through multiple standardized driving schedules to simulate city and highway motoring. The basic city-driving program replicates a rush-hour stop-and-go driving experience with frequent idling. The highway circuit is designed to emulate rural and interstate freeway driving at higher speeds, without making any stops.

An electric vehicle is tested after being parked overnight, and with the battery fully charged. It’s then operated through successive city or highway driving cycles until the battery becomes depleted. It’s then brought back to a full charge. A technician determines the vehicle’s energy consumption by dividing the kilowatt-hours of energy needed to replenish the battery by the number of miles driven. The latter is also used to determine an EV’s estimated operating range on a charge.

To help consumers compare the energy consumption of electric cars with those that run on fossil fuel, the EPA created a miles-per-gallon equivalent measurement, called “MPGe.” This is calculated based on a conversion factor of 33.705 kilowatt-hours of electricity equaling one gallon of gasoline.

For 2018, the EPA’s most energy-efficient EV is the Hyundai Ioniq Electric, with a rating of 150 MPGe in city driving and 122 on the highway. The next-highest 2018 models are the Tesla Model 3 Long Range at 136/123 MPGe, the Chevrolet Bolt EV at 128/110 MPGe, and the Volkswagen e-Golf at 126/111 MPGe.

FUDGE FACTORS

Unfortunately, there are elements inherent in the EPA’s testing procedures that tend to skew the ratings. For starters, vehicles are tested without a full load of passengers, cargo and options aboard. All else being equal, the heavier a vehicle’s rolling weight, the more energy is needed to reach and maintain a given speed.

Also, the tests are conducted indoors at room temperature. An electric car’s range tends to suffer when subjected to extremely cold or hot weather. This is both because of the adverse effects of high and low temperatures on a battery’s charge, and the drain caused by operating the heater and air conditioning.

What’s more, a given motorist’s driving habits can also affect an EV’s energy consumption. Lead-footed acceleration and driving at higher speeds will tend to drain the battery faster than will maintaining a smooth and steady pace. Driving on under-inflated tires will also cost an EV owner additional kilowatt-hours of electricity.

READING AN EV’S ‘FUEL ECONOMY’ STICKER

The federal government requires automakers to include information on a vehicle’s energy consumption, along with pricing and other information on the so-called “Monroney” sticker that’s posted on every new light-duty vehicle sold in the U.S. It’s named for Almer Stillwell “Mike” Monroney, a U.S. Senator from Oklahoma who sponsored the Automobile Disclosure Act of 1958 that mandated the use of price stickers.

In the case of electric vehicles, the Monroney sticker prominently displays the MPGe estimates for city, highway and combined city/highway driving. The latter assumes 55 percent city driving and 45 percent on the highway. The sticker also shows the number of kilowatt-hours of electricity that’s needed to run the vehicle for 100 miles (this is expressed as kWh/100 mi). The EPA says this measurement is actually more meaningful when comparing costs and energy consumption between EVs than the MPGe rating.

The sticker also notes, on average, how many miles the vehicle can operate on a charge, and how long it takes to fully replenish a discharged battery using a 240-volt (Level 2) charger. You can expect the time to typically double when using a standard household outlet.

The window sticker further notes the energy consumption range for other models in the vehicle’s size class. You’ll also find the average annual cost to keep the car or truck running, based on 15,000 miles driven at a predetermined price per kilowatt-hour for electricity. It also shows how much more or less that amount is compared to the average vehicle over a five-year ownership period. These numbers will of course, differ for a given driver depending on local energy rates.

The sticker also provides ratings on a 1-10 basis for a vehicle’s smog-related tailpipe emissions and greenhouse gas emissions. Since full electric vehicles produce neither of these they automatically receive a rating of 10.

You’ll also find a “QR” code that can be scanned by a smartphone and takes users to a website where they can enter information about their commutes and driving habits to get a better estimate of their energy consumption and costs.

The above information can also be found on the EPA’s fueleconomy.gov website for easy comparison among competing models, and it’s available for all current and past plug-in and conventionally powered vehicles.

Be sure to check out other helpful information on electric vehicles here on MYEV.com, which is also the Internet’s prime – and free – marketplace for buying and selling EVs.

Source: MYEV.com

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27 Comments on "How The EPA Rates Electric Cars: Range, Efficiency & More"

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Eco

During dyno tests the car is not moving. If all the testing is on a dyno, how do they test the car’s aerodynamics?

philip d

They use a multiplier. Small one for city since below 40-45 mph there is little aero effect and larger multiplier for highway speeds.

Eco

Yes, I realize the aero drag increases exponentially with speed, but do they use a standard multiplier or use the manufacturer’s stated coefficient of drag? Either way it appears that the EPA’s stated power consumption/range is theoretical, at least at higher speeds!

G2

Especially so given the excellent aero of the TM3

Nix

There is an additional test, called the “coastdown” test that measures the vehicle as it slows from 75 mph down to 5 mph. This provides the coefficient.

Mint

You make a great point in that this article is severely lacking for a “how it works” piece.

The car is put in neutral and let coast down from 80 mph to zero on a long, flat straight. Aerodynamic drag, tire losses, and drivetrain losses all contribute to the car’s speed versus time under this test, and using F=ma, you can deduce total drag as a function of speed. By fitting three coefficients to this function, you can approximate it as Fd = A + Bv + Cv².

You then put these coefficients and the car’s mass into the dyno program, and as the car’s wheels turn the dyno, it applies the appropriate force. There is also a correction factor to make sure the test isn’t double-applying any forces (e.g. the tire effects from the coastdown coefficients plus tire effects from the car actually sitting on the dyno).

As for it being too theoretical, the EPA increases consumption by ~40% (reduces MPGe by 30%) to account for real-world factors. The accuracy depends on the manufacturer being honest about the coefficients from the coastdown test.

G2

How is regen taken into account?
An experienced EV driver doesn’t go from ‘gas-to-brake-to-gas’ like a LICE driver does, they anticipate the stop, or slow down, and remove their foot from the accelerator allowing regen for a while before applying the brake for the last 30km/h of stopping.

Light

I do believe that utilize the regen when slowing down. So for the city numbers it would be in there somewhat. But again since the car isn’t moving in the wait isn’t there, it’s pretty much a joke in that regard.

Jon

The cycles have plenty of deceleration in them, so regen is accounted for. Pressing the brake pedal in most EVs is still primarily regen, rather than friction brakes. Most BEVs can stop on almost entirely regen.

If you are asking if the cycles are different than ICE vehicles, no; same profiles.

Mint

The dyno applies the force to the wheels. You enter the car’s mass into the program, and it knows how much force to apply to the tire to simulate braking. The car’s drivetrain applies regen the same way as it does on the road.

Light

Going from 240 volt to a 120 volt outlet is going to be way more than double the charge time. That would only apply if your amperage stayed the same. Typically on 240 volt you will be charging at 32 amp or more. On 120 volt odds are you’ll be charging at 12 amp. Possibly 16 if you have a 20 amp breaker. So you are looking at closer to 6 times longer on a typical house 120 volt outlet then if you were charging it 240 volt.

MTN Ranger

Yes. I get about 4 miles per hour on 120V @ 15A circuit. I get 38 miles per hour on 240V @ 50A circuit. Huge difference.

William

“You can expect the time to typically DOUBLE when using a standard household outlet.”

The above expected household charging time should at least say “typically quadruple”, that is unless you are stuck with an older rare Nissan Leaf, that can only Level 2 charge at 3.3 kW.

Michael

I use the following rule of thumb for my 24kWh 2015 LEAF
Level 1 – 5% per hour
Level 2 – 30 % per hour
Level 3 – 2% per minute

Elon

The EPA rating was also created with low highway speeds in mind, that 310 miles on a full charge is more like 240 miles at 80mph

Re-Volted

So maybe it would be better to get a min and max range stated. Would require a lot more testing but people really need to understand how drastically range drops in the winter with the heat on.
Last thing we need is a bunch of “Prius style” drivers hypermileing out of necessity.

evMike

…very interesting article. But I still have a questionmark: de aerodynamic is symulated by increasing the roll resistance on the dyno rollers. But based on what? Manufacturers stated drag coefficient and frontal area? …the next way for possible tweaks and cheats 😉
I have good experience with range simulation based on trip profile and enviromental data, like
https://ecalc.ch/evcalc.php

Nix

No, they multiple the actual test results by a coefficient that is specific for each vehicle, that based on a coastdown test.

Mint

Coastdown is still performed by the manufacturer, so cheating can still happen.

Pushmi-Pullyu

As I understand it, all the tests of this type are performed by the manufacturer. The EPA doesn’t have the resources to test all those cars itself. I’m not sure, but I think I’ve read that the EPA does do some spot checks of its own.

Cheating probably would be hard to hide, since so many auto reviewers perform their own tests. Note the controversy over the inflated values that Ford gave to its PHEVs, and that Ford had to revise them downward. That shows how difficult it is to get away with inflating the EPA ratings.

Apparently things are different under the European test cycles, because auto makers there routinely get away with even highly inflated numbers.

Doggydogworld

They feed the three coefficients from the coastdown test into the dynamometer. It then provides appropriate resistance, e.g. more for a draggy car than an aerodynamically clean one.

They later multiply results by a fudge factor, but that doesn’t come from the coastdown test.

Milfan

This KWH/100 MI and liters/100 km is another nonsense like diesel vehicles.
Unit of distance is km or miles
Unit of energy is KWh or liter or gallon.

Ideally it should be miles / KWh in USA and km / KWh in rest of the world where metric is used.
I wish EPA changes to miles / KWh. What made them bring this / 100 miles into picture, is it meant to confuse people or european influence.

Nix

miles per kWh has the same flaw as miles per gallon. It exaggerates energy savings at higher levels of efficiency.

For example, 16 mpg vs. 19 mpg doesn’t seem like much difference at all, while 60 mpg vs. 80 mpg seems like a huge difference.

But going from 16 mpg to 19 mpg saves almost 200 gallons of gas per year (based on 15K miles/year)
Going from 60 mpg to 80 mpg only saves about 60 gallons of gas per year.

Using kWh/100 miles corrects this illusion.

David D. Nelson

That is the best rationale for the energy/distance unit, though I still prefer the inverse.

Bob R

You can tell this article was written by someone without a good working knowledge of testing. Probably some intern scraped the content off of other websites.

Jon

It is important to emphasize that the charger losses play a large part in the MPGe rating since the energy is measured from the wall.

Bill Howland

However, it is important to emphasize that different car brands’ ‘Vampire Losses’ which might occur only during cold weather – are not tested since the overnight is at reasonable temperatures, and are therefore not taken into account.