A hybrid car is a vehicle that uses two or even more distinct sources of power in order to get propelled. Among the power sources for a hybrid car there are gasoline or diesel fuel, on-board or out-board rechargeable energy storage systems (RESS), hydrogen, wind, compressed or liquid natural gas, solar, coal, wood or other solid combustibles, etc. The term hybrid car/vehicle is used most frequently to refer to hybrid electric vehicles (HEVs) in which an internal combustion engine is combined with one or more electric motors.

As mentioned above, there are other hybrid vehicles beside the hybrid car we will mainly deal with here. Just think of mopeds and electric bicycles. These are the simplest forms of hybrid vehicles. They combine the power from an internal combustion engine or electric motor with the power of the rider?s muscles. Then there are hybrid heavy vehicles like railway locomotives, buses, heavy goods vehicles, ships or mobile hydraulic machinery. Usually, the term hybrid car/ vehicle is used to refer to hybrid electric vehicles. This category includes the following types of automotives: AHS2 (Chevrolet Tahoe, GMC Yukon, Chevrolet Silverado, Cadillac Escalade, Saturn Vue), Toyota Prius, Ford Escape Hybrid, Toyota Highlander Hybrid, Toyota Camry Hybrid, Honda Civic Hybrid, Honda Insight and many others. A petroleum-electric hybrid car usually gets its power from an internal combustion engine (gasoline or diesel engine) and an electric battery.

The beginnings of the hybrid car date back to the late 1900s when David Arthurs, an electrical engineer from Arkansas, invented the braking regenerative hybrid. Besides the hybrid car as mentioned above, which uses two or more different propulsion devices, there are also vehicles which use distinct sources of energy or input types but only one engine. These are also considered by some people to be similar to the hybrid car. Actually the latter should be more appropriately called dual mode vehicles (electric trolleybuses, dual mode buses, flexible-fuel vehicles, etc).

A hybrid car presents a number of advantages from the environmental perspective and there are two sides to consider here. First, there is the aspect of fuel economy, and secondly, the benefit for the environment and, implicitly, for humankind is undeniable in the fight to reduce pollution. These two advantages and benefits brought about by the hybrid car are tributary to at least three elements in the design: the combination of gasoline and the electric motors, a battery with plenty of storage capacity and the possibility to re-capture important amounts of energy, which are normally wasted while braking.