Green Car Glossary: Vehicles, Drivetrains, Emissions, Fuels, Energy

Electric cars at charging stations and Tesla SuperCharger stations in Gilroy, CA [photo: Jack Brown]

Electric cars at charging stations and Tesla SuperCharger stations in Gilroy, CA [photo: Jack Brown]

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As gasoline prices go up, acronyms like EREV, CNG, and MPGe are becoming more and more common. 

Ever wonder what they all mean? 

Here's your chance to enter a veritable Twilight Zone of terminology--and find out, say, whether a PZEV is related to a PHEV.

(It's not.)

To help you in your journey, our glossary is divided into categories: Vehicle Types, Drivetrains, Emissions, Fuels, and Energy Storage. 

This glossary is by no means comprehensive as new acronyms seem to appear on a daily basis.

Think of it as a starting point, and feel free to add comments about terms we may have missed.


BEV - Battery Electric Vehicle.  A BEV is not a hybrid; it does not have an internal combustion engine (or ICE) and it relies solely on electric power, supplied by a battery pack.  Because BEVs aren't powered by gas, they have zero emissions.  The biggest drawback to pure electric vehicles is their limited range.  Typical BEVs have a range of 70 to 100 miles.  The Tesla Model S is an exception, with its two versions offering EPA-rated driving ranges of 208 miles or, for the pricier model, 265 miles per charge.

The range of battery-electric vehicles can be dramatically affected by the weather--cold weather in particular.  Most BEV manufacturers have built in heaters that warm the battery while the car is being charged.

HEV or HV - Hybrid Electric Vehicle or Hybrid Vehicle.  Whether HEV or HV, it's a hybrid--a car or truck with a standard gasoline-powered engine that also has a high-voltage battery and an electric motor, both of which supply additional power to the vehicle's drivetrain.  All hybrids share the goal of reducing the amount of gasoline used by the vehicle and lowering its emissions, but they tend to go about it in different ways. The Toyota Prius is currently the highest-selling (and probably best-known) hybrid vehicle.

Mild Hybrid - This is a type of hybrid that cannot be driven on electric power alone, even for a short distance. Almost every Honda hybrids to date has been a mild hybrid, though that is changing for 2014 with the addition of the Accord Hybrid and Accord Plug-In Hybrid. Mild hybrids have only one electric motor-generator; "full hybrids" may have one (Audi, BMW, Hyundai, Kia, Mercedes-Benz, Volkswagen, and others) or two (Ford, Honda, Toyota).

2013 Ford C-Max Energi plug-in hybrid, Marin County, CA, Nov 2012

2013 Ford C-Max Energi plug-in hybrid, Marin County, CA, Nov 2012

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PHEV or PHV - Plug-in Hybrid Electric Vehicle or Plug-In Hybrid Vehicle. PHEVs are conventional hybrids that have been modified by enlarging their battery packs and adding the ability to recharge those batteries by plugging them into wall current. Today, plug-in hybrids are offered by Ford, Honda, and Toyota, and there will likely be several more in future model years. Plug-in hybrids have rated ranges of 6 to 21 miles on electric power only (under gentler conditions than most drivers today may be used to). Once their battery packs are depleted, they revert to operating like regular hybrid cars.

EREV - Extended-Range Electric Vehicle. There is great debate in the field about whether a range-extended electric vehicle should be grouped in the category of plug-in hybrids or considered to be its own type.

Unlike PHEVs, which may switch on their engine at any point if power demand is high, an EREV stays all-electric under every circumstance until its battery is depleted. Then its engine switches on to run a generator that provides energy to turn the wheels.The best-known EREV is the Chevrolet Volt; the only other such car offered for sale was the 2012 Fisker Karma, of which about 2,500 were sold before that company ended production.


Hybrid vehicles generally use one of three different methods for supplying power to the wheels.

BAS - Belt Alternator/Starter - A parallel system used by mild hybrids that provides some fuel savings (not as much as a full hybrid) at a relatively low cost.  BAS systems use a large alternator connected by a serpentine belt to the crankshaft.  This allows the gas engine to stop and then quickly restart (at stop lights for example) and also provides some assistance to the gas engine for moving the car.  Now in its second generation and rebranded as eAssist, it's used exclusively by General Motors in Buick and Chevrolet sedans.

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Comments (24)
  1. A well written article.

    Job well done! Thanks!

  2. Thanks, this was my first article for Green Car Reports. Doug

  3. These are good for the first decade of the 21st century but what about the current crop of technologies that could be around in the future but are not well understood now and indeed many do not know exist. These newer technologies will lead energy storage in the future. These would include in any listing of the newer technologies (but not by any means be exhausted)acronyms such as KERS (Kinetic energy retrieval systems) that is based on quantum mechanics, also the newer metal air batteries as in aluminum air and other 'cascade' type energy reactors (lithium air, magnesium air), also paint based nano dot, pit, ball and plate energy absorbers that are working now but are in experimental stages. As well as the many multi-junction solar cells.

  4. George, you've raised some good points. I'm planning on updating the glossary on a regular basis so I'll try to include more about future technologies. Do you think an article focusing just on future green car technologies would be of interest?

  5. Why have you made such specific restrictions on PHEV/PHVs? Why must they only have up to 21 miles of range. Why must they be limited in speed? The EREV moniker is a GM Marketing invention. There is no reason why EREV should even exist. The appropriate distinction is between PHEVs and "blended" PHEVs, wherein the latter has its engine "on" periodically during charge-depleting mode. The Volt is a series PHEV, while the Prius PHEV is a blended power-split PHEV. Easy peasy.

  6. That's a good point. I would call it series and parallel PHEV wherin the first only uses the ICE for running a generator charging the traction battery and the latter does that and is able of driving the car on its own or together with the e-motor.

  7. Calling Prius a "hybrid" already ABUSED the term "hybrid". Prius PHEV is actually a "true" hybrid.

    The reason that EREV is used is b/c Toyota already tainted the world with the technical term of "hybrid" so GM has to make a clear distinction.

    Is the defintion at the powertrain or energy source?

    If it is energy source, then Prius is an ICE and Prius Plugin is a hybrid or dual source vehicle.

    If it is powertrain, then Prius is a hybrid and so are every other ICE that comes with a "mild hybrid" alternator. And Volt is an electric car...

  8. @Xiaolang

    I think you misunderstand what "hybrid" means. Nowhere in the definition does it require the energy to be off-board energy. And one can't just consider off-board energy anyway: Would you consider a dual-fuel vehicle to be a hybrid? One also can't just consider a vehicle with two or more power sources, since then an EV with two in-wheel motors would be a hybrid. I wrote an article on this if you are interested: DOI: 10.1504/IJEHV.2010.033696

    The Volt is a spectacular vehicle, but it's certainly not an electric vehicle. In one of its four modes, the engine powers the wheels directly (something GM kept secret for a long time but did it for efficiency purposes).

  9. Well, before we talk about anything, DEFINE EV, hybrid, plug in hybrid for me...

    What is the definition of "electric"? If it doesn't have any thing to do with the energy source, then it must be the requirement of the driven train. If so, any car with starter motor can be considered as hybrid, starter motor is powered entired by electricity and it can power the wheel briefly b/c it couples the power to the flywheel and then the transmission to the wheel.

    Define the boundry.

    Sure, that mode in the Volt exist, but engine can NOT power the Volt wheel by itself. The main electric motor has to spin in order for that torque to reach the wheel. There is NO clutch to decouple the main traction motor from the wheel.

  10. In addtion, why is a series hybrid NOT consider as electric when BEV is? Battery store electricity as chemical energy. Gasoline is a chemical energy. One converts that chemical energy into electricity. The other converts that chemical energy into heat and the motion then electricity. So, unless you are storing the electricity directly, then BEV is a "series hybrid" as well.

    My point is that as technology changes, those "OLD WORLD" definition is getting blurred.

    Is fuel cell a series hybrid or classified in a similar category as battery operated EV?

  11. How about Lithium air battery that consumes AL in its oxidation process? Is it a series hybrid or BEV?

    Doesn't the technlogy blur the line of definition?

  12. There are more comments in this thread
  13. Actually the term EREV has been officially endorsed by the appropriate SAE committees and is universally used to describe the "BEV becomes serial PHEV" configuration by the engineering community. Other manufacturers also use the same term when approprrate.

  14. So what is a BEV (70-100 miles range) with a range extender (i.e. the coming i3)? Is that an EREV or a BEV... x? EREVs as I understand have something like 25-40 miles range (Karma, Volt) and then use an ICE (oh, here is another acronym) to continue driving electrically for couple hundred miles?!? BEVs with an extender don't do that as I understand ... very confusing.

  15. I think there are people who would label the Volt a BEV with a range extender. Or, as Mr. Felzer mentioned above, a pure PHEV, rather than blended.

    How does the BMW i3 differ from the Volt? (Not wanting to spend half an hour looking it up.)

  16. The i3 is a BEV with an optional range extender (taken from one of BMW's motorcycles). The additional range coming from that range extender is limited to same/less than the traction battery. That's because in the eyes of CARB a BEV only gets gold credits (ZEV regulation) when the ICE delivers same or less range than the car can do on the traction battery alone.
    That is "very" different from the Volt which basically has an unlimited range (~400 miles) and the same power all the time. The i3, as I understand, has limited power while driving with the extender (delivered power from the extender is less than the e-motor could put on the road).

  17. Technically speaking, i3 can have unlimited range as well as long as you keep refilling the 2-3 gallon tank and its performance will suffer...

  18. i3 with REx would be considered as EREV in my opinion...

  19. I agree because the i3 is still emitting fumes while it is in ER mode. It certainly isn't a pure EV while it has the option of a gas engine.

  20. for the clueless among us and for those who just want to bring contention just for fun, the recent 787 event may bring a simple answer.
    If it catches on fire and it is good, then it is ICE.(jets) If it catches on fire and it is bad then it is probably electric
    (batteries). So with new cars how and when there is fire or no fire is deterined by computer algorithms etc. and so the different definitions.

  21. Hey Mr. Doug Smith, where are the compressed air, water (as fuel), and solar vehicles? Maybe in the future we might have magnetics, too.

  22. Fair point. I'll try to include them in an update.

  23. EV OD

  24. Don't you have synthetic diesel over there?

    100% identical on a molecular level (but of course no sulphur or other crap like that, just pure diesel).

    Can be made from leftovers from the food industry, paper/forest industry etc.

    It has nothing to do with the crapy biodiesel (why it's even called diesel is a mystery to me).

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