Green Car Glossary: vehicles, emissions, fuels, electric cars, powertrains energy (updated)

As rules to boost fuel economy and lower carbon emissions in vehicles around the world continue to stiffen, acronyms like EREV, CNG, and MPGe are becoming more and more common. 

Ever wonder what they all mean? 

This glossary is 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.)

DON'T MISS: GM says green-car buyers should consider its diesels: here's why

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.

EDITOR'S NOTE: We originally published this article in June 2013. Four years later, correspondence with reader John Murray prompted us to revise and update it.

2013 Tesla Model S, in July 2017 [photo: David Noland]

2013 Tesla Model S, in July 2017 [photo: David Noland]


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 early pure electric vehicles has been their limited range, which created a significant perceptual barrier for North American buyers. The first generation of electric cars from 2011 to 2015 had ranges of 60 to 90 miles, except for the Tesla Model S at more than 200 miles.

Now, less pricey longer-range cars are hitting the market, specifically the Chevrolet Bolt EV at 238 miles.

READ THIS: Toyota has now sold 10 million hybrids in 20 years, globally

The range of battery-electric vehicles can be dramatically affected by the weather, cold weather in particular.  Most BEV manufacturers have built in heaters and cooling systems that keep the battery within a specific temperature range while the car is being charged.

HEV: Hybrid Electric Vehicle. A  hybrid is 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.

2017 Toyota Prius

2017 Toyota Prius

The Toyota Prius is the highest-selling (and best-known) hybrid vehicle; it's now in its 21st model year.

Mild Hybrid: This is a type of hybrid that cannot be driven on electric power alone, even for a short distance. Honda and GM were the pioneers here. Now virtually every maker will start to fit the latest generation of mild hybrids to at least some models.

The newest type of mild hybrids are known as "48-volt mild hybrids," effectively advanced start-stop systems that provide additional functions beyond restarting the engine.

Mild hybrids have only one electric motor-generator, while"full hybrids" may have one (Audi, BMW, Hyundai, Kia, Mercedes-Benz, Volkswagen, and others) or two (Ford, General Motors, Honda, Toyota).

2017 Toyota Prius Prime and 2017 Chevrolet Volt with Green Car Reports editor John Voelcker

2017 Toyota Prius Prime and 2017 Chevrolet Volt with Green Car Reports editor John Voelcker

PHEV or PHV: Plug-in Hybrid Electric Vehicle or Plug-In Hybrid Vehicle. Plug-in hybrids 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, the first plug-in hybrids were offered by Ford, Honda, and Toyota, and there will likely be several more in future model years.

Plug-in hybrids have rated ranges of 12 to 97 miles on electric power only, though some deliver continuous electric driving 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.

CHECK OUT: Plug-in hybrid problem: buyers don't understand them at all

EREV: Extended-Range Electric Vehicle. There has been much 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, as GM suggested the first Chevrolet Volt should be. (The second-generation Chevy Volt powertrain is essentially a conventional plug-in hybrid.)

Over the years, for simplicity, the convention has turned toward lumping EREVs with plug-in hybrids (which are themselves confusing enough for novice buyers to understand, we should note).

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 extended-range electric car was the first-generation Chevrolet Volt; the only other such cars offered for sale have been the 2012 Fisker Karma (now the 2017 Karma Revero), and the BMW i3 REx (range-extended), which remains on sale today.

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