The Anatomy of the Plug-In Hybrid—Part 1: What the Heck is it?

You wake up in the morning and get ready for work. You go to your car, unplug it from the outlet in the garage (the same one the power drill is plugged into), and off you go. You go to work, stop for groceries on the way back home, pick up your kid, and then go out to dinner, and even though your car is a hybrid, the gasoline engine never goes on. You do your daily driving purely on electricity. The car is almost silent and even though there’s a tailpipe, nothing’s coming out of it. After dinner you decide to go to a movie. Between the restaurant and the theater the electric batteries finally run out of juice so…the regular hybrid system kicks in and you’re back to getting 40 or 50 mpg on gasoline. Until tomorrow.

This is what life might be like with a plug-in hybrid electric vehicle, or PHEV. With additional battery packs added to a conventional gas/electric hybrid, a car can run on electric power alone for somewhere between 20 and 60 miles, at which point it switches over to the hybrid system. Plug-ins, which are not a new idea, may present a logical link between gas/electric hybrids and pure electric vehicles, offering greater efficiency and cleaner emissions than a hybrid, without the risk of running out of juice like a pure EV, or a need for an electric charging infrastructure. According to the Electric Power Research Institute, half of American drivers commute 25 miles or less each day. If these people drove plug-ins, going to the gas station might be something they do only on long trips, and could typically do months of local driving between fill-ups.

Plug-ins are just beginning to come on the market, and their future is still unclear. The first plug-in conversion kit has just recently become available and more are poised to launch soon. For most advocates, though, plug-in retrofits are just a means of leveraging automakers into adopting plug-in technology on a large scale. Conversion kits are not cheap: around $10,000 each. But plug-in hopefuls claim that if automakers would adopt the technology, mass production and accelerated R&D would bring down the price tag to a few thousand dollars more than a typical hybrid, which now cost few thousand more than conventional internal combustion cars.

Most plug-in hybrids that have been created get 100 mpg or more, and because they charge at night when most utilities have lower rates, they cost an equivalent of a few cents per gallon. Plug-ins run on lithium ion (Li-ion) or nickel metal hydride (NiMH) batteries, and recent advances in battery technology, like MIT’s new lithium battery recipe, may improve the charge duration and lower the cost of batteries for plug-ins. If plug-ins attract enough public interest and research dollars, hopes are that it could pave the way for batteries good enough to make pure electric vehicles more practical and affordable.

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