Understanding Plug-in Vehicle Types

All plug-in cars have a charger, electric motor and rechargeable batteries. Unlike pure electric cars, plug-in hybrids—like the Chevy Volt shown here—also have a gasoline engine.

Shopping for a plug-in vehicle can be confusing because the powertrain architectures come in almost as many flavors as Ben and Jerry's. Unfortunately you may have to ask some questions to know which architecture a plug-in hybrid or electric car uses.

Series Plug-in Hybrid

First, there's a "series" plug-in hybrid, which uses the gasoline engine exclusively to turn a generator that provides electricity to the electric motors that turn the wheels. If you drive less than the battery's range, the engine doesn't turn on.

General Motors has taken this approach one step further in the Chevrolet Volt, which can operate on electricity produced solely by the batteries, or with power produced by the batteries and the generator at the same time. GM prefers the term "extended range electric vehicle" to plug-in hybrid since technically all of the power to drive the wheels comes from electricity. But calling it an "electric vehicle" can be confusing since an onboard-gas engine (which produces emissions) is used to power the generator.

Blended Plug-in Hybrids (Parallel and Series-Parallel)

Next, there is the "parallel" plug-in hybrid, which can use power from two separate sources—an electric motor and gasoline engine—to simultaneously to drive the wheels. These may use the electric motor at low speeds, but use both at highway speeds or for rapid acceleration.

If that's not confounding enough, there are blended or "series-parallel" plug-in vehicles that can power the wheels from only the electric motor, only the engine, or both. These vehicles can operate more efficiently than others at both lower and higher speeds, but the electronics are more complicated and costly.

Pure Electric

And finally, pure electric cars are the easiest to understand because they don't have gasoline engines and rely only on electricity stored in batteries. These are known as either all-electric, battery-electric, pure electric, electric vehicles, or EVs.

Different Horses for Different Courses

So which design is better or worse? It all depends on how you ask the question. All-electric vehicles have the simplest architecture and the fewest components, so while their maintenance cost will likely be lower, they offer reduced driving range and may have less total horsepower than vehicles that also incorporate gasoline engines. Similarly, series plug-in hybrids' reliance on a single power source at a time can simpler to manage than blended plug-in vehicles, but they’re more likely to use larger, more expensive battery packs.

Parallel and series-parallel plug-in hybrids may be preferable because of the combination of total potential power and driving range. However, they can’t always claim “zero emissions,” and engineering a smooth ride depends on how well the vehicle management system controls the powertrain in shifting between multiple sources.

Each carmaker will spin its approach as better than the rest. But in the final analysis, you can’t say that one system is always better for all customers. It’s the total package that counts. Which plug-in vehicle best suits your specific driving needs, driving range requirements, sense of style, and pocket book? All electric-drive vehicles are going to be greener than internal combustion engine cars, and—given the power provided right to the wheels—a whole lot more fun to drive. At a certain point, you’ll need to forget about the nuances, and simply go with the electric flow.