What Are HEVs?
Hybrid electric vehicles (HEVs) combine the internal combustion engine of a conventional vehicle with the battery and electric motor of an electric vehicle. Resulting in twice the fuel economy of conventional vehicles. This combination offers the extended range and rapid refueling that consumers expect from a conventional vehicle, with a significant portion of the energy and environmental benefits of an electric vehicle. The practical benefits of HEVs include improved fuel economy and lower emissions compared to conventional vehicles. The inherent flexibility of HEVs will allow them to be used in a wide range of applications, from personal transportation to commercial hauling.
 

Why HEVs?
Hybrid power systems were conceived as a way to compensate for the shortfall in battery technology. Because batteries could supply only enough energy for short trips, an onboard generator, powered by an internal combustion engine, could be installed and used for longer trips. In the old days, we thought that by biasing the system toward battery-electric power and operating on wall-plug electricity as much as possible, efficiency and emissions would then be about as optimal as we could hope for until better batteries came along. The natural conclusion of this concept was that, with better batteries, we probably would not need hybrids at all. But after 20 years of study, it seems that hybrids are taking center stage and electric vehicles are only being used in niche market applications where fewer miles are traveled.

More efficient cars can make a big difference to society in terms of environmental benefits, and the serious deterioration of urban air has motivated regulators to require cleaner cars. Use of production HEVs will reduce smog-forming pollutants over the current national average. Hybrids will never be true zero-emission vehicles, however, because of their internal combustion engine. But the first hybrids on the market will cut emissions of global-warming pollutants by a third to a half, and later models may cut emissions by even more.

HEV Advantages
HEVs have several advantages over conventional vehicles:

Regenerative braking capability helps minimize energy loss and recover the energy used to slow down or stop a vehicle.
Engines can be sized to accommodate average load, not peak load, which reduces the engine's weight.
Fuel efficiency is greatly increased (hybrids consume significantly less fuel than vehicles powered by gasoline alone).
Emissions are greatly decreased.
HEVs can reduce dependency on fossil fuels because they can run on alternative fuels.
Special lightweight materials are used to reduce the overall vehicle weight of HEVs.
The HEVs available for sale are very cost competitive with similar conventional vehicles. Any cost premium that may be associated with HEVs of the future can be off-set by overall fuel savings and possible incentives. Some states offer incentives for HEVs, so to learn if your state offers incentives go to the Fleet Buyer's Guide Incentive Page and search on your state.

Auto manufacturers are making these HEVs with comparable performance, safety, and cost because they know that these three elements are most important to consumers. And by combining gasoline with electric power, hybrids will have the same or greater range than traditional combustion engines. The HEV is able to operate approximately two times more efficiently than conventional vehicles. Honda's Insight is expected to go 700 miles on a single tank of gas. The Toyota Prius is expected to go about 450 miles. For the driver, hybrids offer similar or better performance than conventional vehicles. More important, because such performance is available now, hybrids are a practical way for consumers to chose a cleaner drive today.
 

Types of HEVs
Many configurations are possible for HEVs. Essentially, a hybrid combines an energy storage system, a power unit, and a vehicle propulsion system. The primary options for energy storage include batteries, ultracapacitors, and flywheels. Although batteries are by far the most common energy storage choice, research is still being done in other energy storage areas. Hybrid power unit options are spark ignition engines, compression ignition direct injection engines, gas turbines, and fuel cells. Propulsion can come entirely from an electric motor, such as in a series configuration, or the engine might provide direct mechanical input to the vehicle propulsion system in a parallel configuration system. There are several transmission options when it comes to HEVs as well—the driver that determines which transmission to use is efficiency.

A hybrid's efficiency and emissions depend on the particular combination of subsystems, how these subsystems are integrated into a complete system, and the control strategy that integrates the subsystems. A hydrogen fuel cell hybrid, for example, would produce only water as a by-product and run at greater overall efficiency than a battery-electric vehicle that uses wall-plug electricity.

What's Next for HEVs?
HEVs are now at the forefront of transportation technology development. Hybrids have the potential to allow continued growth in the automotive sector, while also reducing critical resource consumption, dependence on foreign oil, air pollution, and traffic congestion.

Hybrids are a hot subject today and they are beginning to show up on showroom floors across the United States. Their widespread penetration into the automotive market hinges mainly on the economics of producing a complex hybrid power system, rather than the inherent capabilities of the technology itself. The hybrid's complexity, and the fact that some of the best storage and conversion systems have yet to be fully developed, is responsible for varied opinions on hybrids' ultimate impact in the marketplace. As with any new technology, there may be obstructions to its ready acceptance by consumers. But time will soon tell. The Honda Insight is available to United States consumers now, and so far its been getting a lot of attention. Similarly, the Toyota Prius has been available for sale in Japan since December 1997 and has been a hot seller. It goes on sale in the United States in June 2000. To help with market acceptance, federal and state incentives are in place to off-set some of the HEV purchase costs.