Lithium Economics

Is the Volt a Range-Extended Electric Vehicle?

Mar 26, 2011

A recent exchange of views on the definition of the Volt between Juan Carlos Zuleta and an anonymous reader

 In a recent comment on my article entitled: ”Lithium for Hybrids: Is Nickel  for Batteries Dead?, an anonymous reader said:

“I am curious as to what you consider to be a "regular PHEV". GM invented the term EREV (note: not REEV), but there is really no difference between the two. A PHEV is simply an HEV that takes some of its energy from off-board sources. Contrary to what the General would have you believe, there is no provision that a PHEV not be capable of full all-electric driving. The EREV term is even more suspect now that details on the Volt powertrain have been released and that the engine does power the wheels directly (i.e. mechanically) in charge-sustaining mode above a certain speed (72 mph I believe). I agree with the rest of the article.

My first response was:    

There is really no consensus about which term to use (either REEV or EREV) (See, for; and Not to engage in an endless and fruitless discussion about it, I would prefer to use the terms interchangeably. Regarding the issue of whether the Volt is a PHEV or a REEV (or EREV), I suggest you to see an interesting explanation about the Volt technology provided by a GM chief in October 2010 so that you can draw your own

Since the reader was not very happy with my explanation, he (she) came back with the following remarks:

“That article doesn't explain the difference between PHEV or EREV--probably because there isn't one. That is why I was wondering what you meant by "regular PHEV". The Volt is simply a PHEV that operates as a series hybrid up to 72 mph and then as a power-split hybrid beyond this speed in its charge-sustaining mode (in addition to the all-electric or charge-depleting mode). The drivetrain design is indeed ingenious, so my quibble is only with the introduction of a term that confuses people and is actually misleading. The vehicle is certainly not an electric vehicle: it has clearly been hybridized with the ICE. The Volt is no more an EV than the plug-in Prius (coming in 2012 or 2013) will be. The definition of an HEV is a vehicle with two or more power sources, and the PHEV term is simply an HEV that takes some of its energy from off-board sources. There is no way that a vehicle with an ICE on board in addition to a battery pack can be called an EV. So the PHEV moniker is much more accurate and the need for the EREV (or REEV) term is superfluous at best.

Even though I believe this issue is not closed, here is my latest response:

First, by “regular PHEV” I meant a parallel hybrid (i.e. a vehicle in which “both the mechanical power output and the electrical power output are connected in parallel to drive the transmission” where “ICE is basically always in on mode and operates at almost constant power output at maximum efficiency point”. See:, which takes part of its energy from external sources. An example of a regular PHEV would be the Toyota PHEV to be launched in 2012. 

Second, following the Automobile Magazine (See:  the Volt is much more than a PHEV because it: (1) essentially functions as a battery EV for a 40 mile range; (2) can get more power from its second electric generator/motor when it exceeds 50 mph; (3) can have its gasoline engine automatically started to connnect to the smaller electric generator/motor to recharge its battery once it´s is depleted or reaches a 30% or so state for charge; (4) operates as both a series hybrid (i.e. “a vehicle that has no mechanical connections between ICE and wheels”. See: ) and a parallel hybrid (as defined above) at higher cruising speeds; and (5) has regenerative breaking as all hybrids and EVs. 

Finally, I agree that the term REEV (or EREV) may not be sufficient to describe all 5 functions of the Volt, but do you have an alternative suggestion?

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