It certainly could be confusing to new EV shoppers. EV (Electric Vehicle) now typically refers to cars that you can plug in to charge an on-board traction battery, a fairly large battery typically made of lithium ion battery chemistry (similar to what we use in laptops and smart phones) that stores and provides energy to move the car. The name traction battery is used to distinguish it from the regular 12V battery that provides starting, lighting and other electric powered functions. Traction batteries are typically high voltage and must be handled with care by trained technician during service. So EVs are also known as plug-ins, to distinguish it from the earlier non plug-in hybrids heralded by Toyota Prius.
In the past couple years diverse EV designs appeared on the market that defined several subclasses of EVs. First, EVs are divided into two subclasses, BEV (Battery Electric Vehicle) and PHEV (Plug-in Hybrid Electric Vehicle). BEV is basically pure electric, where you are required to stop and charge the traction battery once it's drained (known as range anxiety). Nissan Leaf and Tesla Model S belong to this category. PHEV on the other hand is more flexible, it typically provides a gas-powered mode where you could continue to drive on gas just like a traditional car, even if the traction battery is completely drained.
Within the PHEV category, enough differences in design approach warrants further classification. It mainly hinges on the degree of focus on, electricity or gasoline powered mode. There are evolutionary designs from the earlier hybrids (non plug-ins), which place electricity power more towards an assisting source of power, represented by Toyota's Prius Plug-in. There is also designs such as BMW i3 that places main focus on electric power, while gasoline power only charges the battery rather than directly moving the car. This approach is known as serial hybrid. The i3 even made the gasoline power optional, so that it can be ordered as BEV as well. Another design from General Motors for Chevrolet Volt also places more focus on electric power but maintaining a more balanced approach between electricity and gasoline.
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| Drivetrain Illustration of Chevrolet Volt |
Currently, the market classifies the designs such as i3 and Volt into EREV (Extended Range Electric Vehicle). California government now defines a subclass of EREV known as BEVx (Battery Electric Vehicle extended) which significantly limits gasoline power mode, and currently only includes the BMW i3 with range extender.
So if you believe EVs are the future of auto industry, then ranking by degree of pureness, it's BEV, BEVx, EREV, PHEV. Typically, it also shows with the battery capacity and EV range of the car. The more EV range of the car, the larger the capacity of the traction battery, the more design focus is placed on electric power.
In my personal opinion, BEVx and EREV could represent the best overall values to EV market in the near term due to their added versatility. However this is rather a close call to BEV, as battery technology progresses rapidly and fast charging infrastructure develops, BEV could certainly take over due to its mechanical simplicity, lower cost of maintenance and potential better durability. BEVx may very well stay competitive though, as we have seen the cost of range extender option in i3 as less than $4000. It's quite conceivable that this extra cost could further drop as the production volume scales and the lower end of the market picks up the design.
