Hybrid Electric

A hybrid electric vehicle (HEV, or "hybrid") uses both electrical and mechanical energy to propel it. It combines the efficiency of electrical drive systems with the longer driving range provided by liquid or gaseous fuels.

From the 1830s until the 1920s, electricity, stored in lead-acid batteries, was popular energy source for vehicles. Electricity is a highly efficient means of propelling vehicles; the range of battery electric vehicles is relatively short, however, because the energy density of batteries is low compared with that of liquid or gaseous fuels. When petroleum became an inexpensive and widely available fuel, electric vehicles lost their popularity as long-distance vehicles. Because of their quiet operation and lack of exhaust, they continued to be used off road in factories, warehouses and golf courses.

Hybrid power systems were conceived as a way to extend the range of electric vehicles for on-road use. Early designs assumed that HEVs would get most of their power from wall-plug electricity. For longer trips, an onboard generator powered by an internal combustion engine would extend the power needed. This system was expected to be as efficient and emission free as possible until better batteries were developed that made hybrids unnecessary.

In recent years, design approaches for HEVs have changed. They no longer rely on wall-plug electricity and are no longer seen as traditional vehicles. Most experts feel that the care of the near future will be an HEV of some kind.

From 1993 to 2002, two programs supported research and development of hybrid vehicles in the United States: the Department of Energy’s HEV Program and the Partnership for a New Generation of Vehicles (PNGV) Program. The latter was a collaboration between the federal government and the Big Three automakers – Ford, General Motors and DaimlerChrysler. The goals of the two programs were closely aligned. The HEV Program aimed to develop HEV drivetrains and other internal components that would be twice as fuel efficient as those of conventional vehicles. The PNGV Program researched vehicle characteristics that affect fuel efficiency – such as the chassis, body, aerodynamics, and rolling resistance – with the goal of developing HEVs that achieve up to 80 miles per gallon, or three times the fuel economy of conventional 1993 vehicles.

Auto manufacturers throughout the world are interested in HEVs. The Japanese were to the first to market them: Toyota introduced the first HEV in Japan in 1997. In 1999, Honda sold the first gasoline-electric hybrid in the United States.

The first model hybrids depended on gasoline, but hybrids can be designed to operate on a wide variety of gaseous or liquid fuels, including fossil fuels or a renewable alternative fuel such as biodiesel or ethanol.

Hybrids essentially combine a mechanical power unit, an electrical energy storage system, and a propulsion system. Many combinations or configurations are possible. The power unit may be a spark-ignition engine, compression ignition direct-injection engine, gas turbine, or fuel cell. The energy storage system may be a battery, ultracapacitor, or flywheel. Propulsion may come entirely from the electric motor or from both the motor and power unit.

Several vehicle alterations lead to greater fuel economy for hybrids than with traditional vehicles. If an internal combustion engine is used, the engine can be smaller and lighter because it shares the workload with the electrical motor. The engine can be optimized to operate within a speed range where fuel economy is greatest. HEVs typically use regenerative braking, which slows the vehicle by capturing kinetic energy, converting it to electricity, and channeling it to the battery pack, thus minimizing the energy lost when slowing down.

Because HEVs have combined systems, they are more complex than either battery-powered or conventional vehicles. Maintenance schedules and the cost of parts and service are expected to be higher than for other types of vehicles.

Care needs to be taken in transporting and refueling whatever gaseous or liquid fuel is used to power the hybrid. For batteries, vehicle manufacturers are using a number of disconnect systems in the high-voltage circuits, which isolate the rest of the vehicle from the battery voltage. Lethal levels of electricity may be present in the battery pack, however, so it should be treated with the same caution and respect as a full fuel tank in an internal combustion vehicle. In case of accidents, emergency response personnel will need special training to handle such hazards as exposure to high-voltage systems and possible leakage of flammable, toxic or corrosive battery chemicals and/or fuel.

HEVs are meeting or exceeding the performance of conventional vehicles.

Gasoline-powered HEVs are rapidly refueled and need fueling less often. Toyota Motor Company reports that its Prius, the first gasoline-powered HEV, gets 48 combined highway/city miles per gallon. According to Honda, its Insight – the first hybrid sold in the United States – gets 61/68 city/highway miles per gallon. U.S. automakers aim to create a vehicle getting 80 miles per gallon.

Because hybrids are two to three times as fuel efficient as conventional vehicles, emissions per mile are greatly decreased. The type of emissions depends on the by-products of the specific fuel used. The first hybrids, which use gasoline, cut emissions of greenhouse gases by a third to a half; later model may cut emission even more.

Toyota Motor Company reports that the Prius greatly reduces emissions: 50 percent for carbon dioxide and 90 percent for carbon monoxide, hydrocarbons, and nitrogen oxides. The Prius is rated by the California Air Resources Board as a super ultra low-emission vehicle (SULEV), and the Insight is rated as an ultra low-emission vehicle (ULEV).

Thanks to the Northeast Sustainable Energy Association (NESEA) for providing this information.

To learn more about electric vehicles, visit the Electric Vehicle Association of the Americas. Easy Breathers also has a profile of electric vehicles expert Michael Hackleman.