| Micro or "mild" hybrid |
Vehicles with ICEs, larger batteries, and electrically powered auxiliary systems that allow the engine to be
turned off when the vehicle is coasting or idle and then be quickly restarted. Regenerative braking recharges
the batteries but does not provide power to the wheels for traction. Micro and mild hybrids are not connected
to the electrical grid for recharging and are not considered as HEVs in this analysis. |
| Full hybrid electric (HEV) |
Vehicles that combine an internal combustion engine with electric propulsion from an electric motor and
battery. The vehicle battery is recharged by capturing some of the energy lost during braking. Stored energy
is used to eliminate engine operation during idle, operate the vehicle at slow speeds for limited distances, and
assist the ICE drivetrain throughout its drive cycle. Full HEV systems are configured in parallel, series, or power
split systems, depending on how power is delivered to the drivetrain. HEVs are not connected to the electric
grid for recharging. |
| Diesel |
Vehicles that use diesel fuel in a compression-ignition internal combustion engine. |
| Plug-in hybrid electric(PHEV) |
Vehicles with larger batteries to provide power to drive the vehicle for some distance in charge-depleting mode,
until a minimum level of battery power is reached (a "minimum state of charge"), at which point they operate on
a mixture of battery and internal combustion power ("charge-sustaining mode"). The minimum state of charge
is engineered to about 25 percent of full charge to ensure that the battery's life cycle matches the expected
life of the vehicle. PHEVs also can be engineered to run in a "blended mode," using an onboard computer to
determine the most efficient use of battery and internal combustion power. The battery can be recharged either
from the grid by plugging a power cord into an electrical outlet or by the internal combustion engine. Current
PHEV batteries are designed to recharge to about 75 percent of capacity for safety reasons related to battery
overheating, leaving a depth of discharge of around 50 percent of total battery capacity. Typically, the distance a
fully charged PHEV can travel in charge-depleting mode is indicated by its designation. For example, a PHEV-40
is engineered to travel around 40 miles on battery power alone before switching to charge-sustaining operation. |
| Plug-in electric (EV) |
Vehicles that operate solely on an electric drivetrain with a large battery and electric motor and do not have an
ICE to provide motive power. EVs are recharged primarily from the electrical grid by plugging into an electrical
outlet, with some additional energy captured through regenerative braking. EV batteries also have a working
depth of discharge capacity that is limited to both lower and upper levels due to life-cycle and safety concerns.
EVs are designated by the distance a fully charged vehicle can travel in all-electric mode. For example, an
EV-100 is designed to travel around 100 miles on battery power. EVs lack the "range extender" capability of
PHEVs, which can switch instantly to an ICE when the battery reaches a minimum state of charge. |
