Electric Vehicle Definitions
Miles per Gallon Equivalent (MPGe)
MPGe is similar to MPG, but instead of representing miles per gallon of the vehicle’s fuel type, it represents the number of miles the vehicle can travel using a quantity of fuel with the same energy content as a gallon of gasoline. This allows a reasonable comparison of energy efficiency between vehicles using different fuels, such as electric cars and gasoline-powered cars. However, the cost per mile and emissions per mile are the best comparisons between vehicles using different fuels to understand their impact on your wallet and the environment.
kWh (kilowatt hours) is a measure of energy, equal to using 1000 Watts for 1 hour. kWh/mile is therefore a measure of the efficiency of electric vehicles. A lower number indicates a more efficient vehicle. Current full-size EVs have efficiency in the range of 0.28 – 0.44 kWh/mi.
Battery Electric Vehicle (BEV)
A battery electric vehicle (BEV) is an all-electric car, which runs entirely on an electric motor and rechargeable battery. As compared to a gasoline engine, an electric motor is much more efficient and mechanically simple.
Plug-in Hybrid Electric Vehicle (PHEV)
A plug-in hybrid is a type of hybrid vehicle that takes electricity from an outlet to recharge internal batteries. The energy stored in the batteries can be used to drive an electric motor, just as in a BEV. However, a PHEV also has an engine, typically gasoline-fueled, which can power the vehicle when the battery is depleted. The manner in which the engine is used differs among hybrid vehicles, but it is used in one of the following three ways:
This is the simplest hybrid configuration. In a series hybrid, the electric motor is the only means of providing power to get your wheels turning. The motor receives electric power from either the battery pack or from a generator run by a gasoline engine. A series hybrid gives the vehicle the ability to continue to drive even after the batteries are discharged.
With a parallel hybrid electric vehicle, both the engine and the electric motor generate the power that drives the wheels. This increases highway efficiency compared to a series hybrid, but reduces the city driving efficiency benefits compared to series hybrids and battery electric vehicles.
This drivetrain merges the advantages and complications of the parallel and series drivetrains. By combining the two designs, the engine can both drive the wheels directly (as in the parallel drivetrain) and be effectively disconnected from the wheels so that only the electric motor powers the wheels (as in the series drivetrain). As a result of this dual drivetrain, the engine operates at near optimum efficiency more often. At lower speeds it operates as a series vehicle, while at higher speeds, the gasoline engine takes over.