Publication Detail

Hybrid Electric Vehicles

UCD-ITS-RP-98-04

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Suggested Citation:
Sperling, Daniel (1998) Hybrid Electric Vehicles. Oxford Energy Forum (33)

Industry response to calls for cleaner air and less energy consumption has centred on more sophisticated emission controls on conventional gasoline and diesel vehicles, reformulation of gasoline and diesel fuels, and some experimentation with non-petroleum fuels and battery-powered electric vehicles (EVs). These technological responses are not fully satisfactory – batteries are expensive and heavy, reformulated fuels provide minor benefits, alternative fuels burned in ICEs are generally not much of an improvement over petroleum, and emission controls on ICEs don't solve greenhouse gas or energy concerns. Industry and government continue to seek other technological solutions.

A current favourite is fuel cells, which are more energy efficient and less polluting than ICEs and do not have the range limitations of battery EVs. Projected costs are dropping dramatically as research intensifies and designs are improved. But will fuel cell costs drop the additional 90 per cent or so that is needed for them to be competitive with petroleum-powered ICEs? And where will the fuel come from? Fuel cells operate best on hydrogen, but hydrogen poses some safety hazards and is bulky and expensive to store onboard. Other liquid and gaseous fuels are technically feasible but involve tradeoffs in cost, emissions, efficiency, and/or performance.

Which brings us to hybrid electric vehicles, the other major propulsion option for vehicles. Hybrid vehicles combine an electric motor with a combustion engine. By severing the direct connection between engine and wheels, the engine can operate at steady load near its maximum efficiency, as with stationary engines. The engine would be downsized, with onboard energy storage devices such as batteries, ultracapacitors, or flywheels providing the power surges needed for hill climbing and passing.

In some sense, hybrids are a middling technology. They do not have a distinct superiority along any dimension and present a muddled image to consumers. Compared to ICE vehicles, hybrids have better energy efficiency, easier-to-control emissions (since engines are operating at a steady load) and, like all electric-drive vehicles, a superior driving feel (the result of high torque and smoother acceleration at lower speeds). But due to redundant power plants, they are inherently more expensive and possibly less reliable than ICE vehicles. Hybrids have longer range and fewer batteries than battery EVs, but are technologically more complex, generally lack home recharging (which appears to be highly valued in the US market), and present a less pure environmental image.