• HEV Levels

    The term hybrid refers to a type of vehicle. There are different levels of “hybridization” among hybrids on the market including micro, mild, full, and plug-in. Note that most mild and all full and plug-in hybrids have the function of regenerative braking. Regenerative braking is a technology that converts kinetic energy (car movement) into chemical energy stored in the battery when the driver’s foot pushes on the brake. This is done by the car's momentum turning a generator connected to the wheels that charges the battery. For a variety of visualizations of hybrid levels (and types), visit our Simulations Page.

    HEV levels comparison chart


    A micro HEV is a vehicle with an integrated alternator/starter that uses start/stop technology. Start/stop technology is where the vehicle shuts down the engine at a complete stop and then restarts when the driver releases the brake pedal. During cruising, the vehicle is propelled only by the internal combustion engine. Typical fuel efficiency increase is around 10% compared to a non-hybrid. Examples of micro hybrids on the road today are the BMW 1 and 3 series, Fiat 500, SMART car, Peugeot Citroen C3, Ford Focus and Transit, and Mercedes-Benz A-class. 


    A mild HEV is very similar to a micro HEV with the exception that the integrated alternator/starter is upgraded with stronger electric components that assist in vehicle propulsion. Compared to a micro HEV, the electric motor, alternator, and battery pack are larger and play a greater role in the operation of the vehicle. Typical fuel efficiency increase is around 20-25% compared to a non-hybrid. Examples of mild HEVs on the market include the BMW 7 Series ActiveHybrid, Buick LaCrosse with eAssist, Chevrolet Malibu w/ eAssist, Honda Civic and Insight Hybrid, and the Mercedes-Benz S400 BlueHybrid.  

    Full (Strong)

    A full HEV is similar to a mild HEV because it utilizes the same electric components such as an electric motor, alternator, and battery pack, but they’re much larger in size. The differences between a mild and full HEV are a full HEV typically uses a smaller engine, has the ability to propel the vehicle solely off the electric motor, and utilizes a more sophisticated control system to optimize efficiency. Typical fuel efficiency increase is around 40-45% compared to a non-hybrid. Examples of full hybrids on the road today are the Chevrolet Tahoe Hybrid, Toyota Prius and Camry Hybrid, Ford C-Max, Honda CR-Z, and Kia Optima Hybrid.

    Plug-in (PHEV)

    A PHEV is essentially the same configuration as a full HEV, but utilizes a more downsized engine and even larger electrical components such as the electric motor, alternator, and battery pack capable of charging off the electrical grid through a plug. PHEVs may run solely on electric power for the charge of the battery, which can be as high as 60 miles until the engine must start. While the engine operates, fuel efficiency is similar to a full HEV. PHEVs are ideal in urban commuting where trips are short, but are also equipped for long trips. Examples of PHEVs on the road today are the Chevy Volt, Ford C-Max Energi and Fusion Energi, Fisker Karma, Porsche Panamera S E-Hybrid, and Toyota Prius Plug-in.