Hybrid Electric Vehicles
There are even some hybrid electric trolleys on the road.
Today hybrid electric vehicles (HEVs) are a familiar sight on the road. They're everywhere, from small cars and SUVs to large trucks. On the outside, some are even indistinguishable from conventional vehicles.
But unlike a conventional vehicle, a hybrid electric vehicle typically combines an internal combustion engine with an electric battery and electric motor. This combination offers greater fuel economy and fewer emissions compared to a conventional vehicle.
Hybrid electric vehicles are powered by two energy sources: an energy conversion unit, such as a combustion engine or fuel cell, and an energy storage device, such as batteries and/or ultracapacitors. The energy conversion unit may be powered with gasoline or an alternative fuel. The electric battery is recharged through an onboard generator or regenerative brake. A regenerative brake recaptures some of the kinetic energy that would otherwise be lost as heat when braking.
There are two types of HEV designs:
Parallel design—the energy conversion unit and an electric propulsion system are connected directly to the vehicle's wheels. The vehicle uses the primary engine for highway driving, and the electric motor provides additional power during acceleration, hill climbs, and other periods of high demand.
Series design—the primary engine is connected to a generator that produces electricity. The electricity charges the batteries, which drive an electric motor that powers the wheels.
Hybrid electric vehicles also can incorporate both parallel and series designs. Another type of hybrid electric vehicle is the plug-in hybrid, which has an electric battery that can be recharged using a standard 110-volt outlet.
NREL's hybrid electric vehicle research falls under advanced vehicle systems and heavy hybrid propulsion systems.
Also see the U.S. Department of Energy's, What is a Hybrid Electric Vehicle? for more information.
