How do they work? Hybrid electric vehicles (HEVs) are powered by two energy sources-an energy conversion unit (such as a combustion engine or fuel cell) and an energy storage device (such as batteries or ultracapacitors). The energy conversion unit may be powered by gasoline, methanol, compressed natural gas, hydrogen, or other alternative fuels. Hybrid electric vehicles have the potential to be two to three times more fuel-efficient than conventional vehicles. HEVs have either a parallel or series design. In a parallel design, the energy conversion unit and electric propulsion system are connected directly to the vehicle's wheels. The primary engine is used for highway driving; the electric motor provides added power during hill climbs, acceleration, and other periods of high demand. In a series design, the primary engine is connected to a generator that produces electricity. The electricity charges the batteries and drives an electric motor that powers the wheels. Unlike electric vehicles, the batteries in HEVs don't need to be plugged in to recharge. Instead, they are recharged using regenerative braking. This means the battery is charged whenever the brakes are used. Are they available in the marketplace today? The Toyota Prius, Honda Insight, and Honda Civic Hybrid were introduced in the United States in 1999, 2000, and 2002 respectively. These and other hybrids are currently available. HEVs do not qualify for Energy Policy Act (EPAct) credits. For more information on vehicles that meet EPAct regulations, visit the EPAct Web site, and download Commercially Available Hybrid Electric, Low-Speed Vehicles not Eligible for EPAct Credit. Recent tax credits available to purchasers can be found here. Is maintenance more expensive with a hybrid? There's no reason why maintaining a hybrid should cost any more than a conventional car. You'll probably want to take your hybrid to a dealer, especially considering that Toyota offers a 100,000 mile warranty on the electric fuel cells and battery and that Honda offers an 80,000 mile warranty on the same-on top of the traditional 3-year/36,000 mile warranty on the conventional systems. Dealer service centers do usually charge a little more, but classes are popping up all over the country to teach independent car mechanics about hybrids. After all, there will be hundreds of thousands of these cars on the road in the next couple of years, and mechanics will have to meet this demand. This timing works out well for new hybrid buyers. By the time your warranty is finished, there will be many more qualified hybrid mechanics available to you. How often do hybrid batteries need replacing? Is replacement expensive and disposal an environmental problem? The hybrid battery packs are designed to last for the lifetime of the vehicle, somewhere between 150,000 and 200,000 miles. The warranty covers the batteries for between eight and ten years, depending on the car maker. Some detractors doubt that the batteries will truly last that long, so only time will tell. Hybrids use NiMH batteries, not the environmentally problematic rechargeable nickel cadmium. "Nickel metal hydride batteries are benign. They can be fully recycled," says Ron Cogan, editor of the Green Car Journal. Toyota and Honda say that they will recycle dead batteries and that disposal will pose no toxic hazards. Will hydrogen fuel cell technology wipe out hybrids? Most experts agree that cars powered by hydrogen fuel cells will not hit the market for another ten to twenty years. It's likely that the first set of hydrogen-powered cars will use more than one energy source, and thus will be considered hybrids. Other Resources Advanced Research Projects Agency (ARPA) The Advanced Transportation Technology Institute Advisor Advanced Vehicle Simulator (ADVISOR) CALSTART The Center for Advanced Vehicle Technologies (CAVT) DOE's Hybrid Electric Vehicle Web Site Drive Hybrid Cars Electric Auto Association (EAA) Engine Technology Progress in Japan FutureTruck Northeast Advanced Vehicle Consortium (NAVC) Society of Automotive Engineers (SAE) USCAR