Alternative Fuel Vehicles (AFVs) — AFVs use energy sources other than gasoline. Historically, cars have been powered by an array of sometimes eccentric energy sources, from clockwork motors to used cooking oil, with varying degrees of success.

The U.S. Department of Energy (DOE) list of alternative fuels includes alcohol, compressed natural gas, electricity, hydrogen, liquefied natural gas, liquefied petroleum gas, coal-derived liquid fuels, and fuels other than alcohol made from biological sources, such as soybeans.

While several of these alternatives are in use today (mostly in commercial fleets), only electricity promises to deliver a zero emission vehicle powered by an energy source that is, at least theoretically, cheap and inexhaustible. At present, electricity is the only fuel that can meet California’s mandate for zero emission vehicles (ZEVs).

The California mandate — Under a federal act permitting California to set emission standards stricter than national standards, the state introduced the first-ever requirement for ZEVs in 1990. Originally, zero emission vehicles were to be introduced in 1998, with escalating phase-in standards until 2003, when 10 percent of new vehicles sold would be ZEVs. The timetable was later altered, with the 2003 standard alone remaining, although modified so that the 10 percent could be composed of 4 percent ZEVs while the remaining 6 percent could be extremely clean cars such as hybrids.

ZEVs — Most AFVs are basically gasoline cars modified to burn other fuels (which pollute, although usually less than gasoline does). Only electric vehicles meet ZEV requirements. There are two principal types: battery and fuel cell. Two others, solar powered (gathering sufficient solar power in a car has proven an elusive goal) and hybrid, also exist.

A hybrid uses both an electric motor and an internal combustion engine, and is not a ZEV. However, hybrids and extremely clean gasoline cars may eventually deliver most of the benefits that electric cars would were they practical; politics likely will play as big a role as technology in what happens. Honda and Toyota both currently offer hybrids. The price of each begins at about $21,000.

Battery electric — These cars carry rechargeable batteries to power a motor. They’ve been the car of the future for more than a century and inspire an almost religious fervor among some advocates. But a scientific breakthrough that would provide the affordable, long-lasting, quickly recharged battery needed to make this car competitive remains, as it has for a century, just over the horizon. Battery electric pluses include clean and silent operation. Minuses include short driving range (50 to 130 miles), long refueling time (two to 10 hours), and the need for periodic battery replacement. Use of lights, wipers, air conditioning, or any other electronic features reduces the range. Electric vehicles are offered by Daimler Chrysler, Ford, GM, Honda, Toyota, and Nissan. Some models are for fleets only and most others are for lease only. Purchase prices can range between $33,000 and $50,000.

Fuel cell electric — Fuel cells produce electricity from hydrogen. The by-product is water. Fuel cell pluses include very clean vehicles, use of a possibly inexhaustible energy source, and an operating range comparable to that of gasoline cars. Minuses include vehicle cost and the difficulties of manufacturing and distributing enough hydrogen for wide-scale use of fuel cell vehicles. Chrysler introduced America’s first drivable, zero emission fuel cell car, NECAR 4, last year and hopes to have it in limited production by 2004.

Information — The Web is full of AFV information. Three excellent sites are the California Air Resources Board, at www.arb.ca.gov; the Alternative Fuels Data Center, www.afdc.nrel.gov; and the U.S. Department of Energy, www.eren.doe.gov.