Primer: The Benefits of Plug-In Hybrids

prius-plug-inPlug-in hybrid electric vehicles (PHEVs) combine the functionality of a gasoline-electric hybrid with the zero-emission capabilities of an all-electric vehicle. Unlike conventional hybrids that rely solely on an internal combustion engine and regenerative braking to charge their batteries, PHEVs also allow batteries to be charged through an electrical outlet or EV charging station.

A PHEV’s battery pack is significantly larger and more powerful than a conventional hybrid, but still quite smaller than that of a dedicated battery electric vehicle. Thus, a PHEV’s electric driving range is shorter than an electric vehicle. Still, the added functionality of 20 to 40 miles of zero-emission electric driving is a real plus to many hybrid owners.

2011 Chevrolet Volt Battery Animation

Examples of PHEVs already available to U.S. consumers include the BMW 13 and i8, Chevrolet Volt, Cadillac ELR, Ford C-MAX Energi, Ford Fusion Energi, Honda Accord Plug-in Hybrid, Porsche Panamera S E-Hybrid, and Toyota Prius Plug-In. Other PHEVs from various automakers are in the works.

The larger battery pack in a PHEV can add several thousand dollars to a hybrid’s purchase price. For example, Ford’s Fusion and C-MAX Energi models use a 7.6 kilowatt-hour lithium-ion battery that provides about 21 miles of electric-only driving. This compares to the smaller and less expensive 1.4 kilowatt-hour battery in Ford hybrids without plug-in capability. The kilowatt-hour capacity of a battery is an indicator of the miles a PHEV can travel in electric-only mode, much like the gasoline in a conventional car’s tank indicates its range.

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A PHEV’s greatest advantage is that driving range is not limited by the finite battery capacity carried on board, thus there is no ‘range anxiety.’ Once battery power is depleted, a PHEV reverts to conventional gasoline-hybrid operation or, depending on its configuration, powers its motors with electricity created by an on-board internal combustion engine-generator. For this reason, PHEVs are often called extended range electric vehicles (EREVs).

Calculating PHEV fuel economy is complicated due to differing operating modes – all-electric with no gasoline used, combined electric and gasoline use, and gasoline-only operation. Plus, series and parallel plug-in hybrids operate differently. For this reason, federal PHEV fuel economy labels have been established to illustrate a plug-in hybrid’s expected efficiency measured in miles-per-gallon (MPG) when running on gasoline-electric hybrid power and MPGe (miles-per-gallon equivalent) when running on electricity.