Fleet Management Department
Electric Vehicles - About Electric Vehicles
Department of Energy EV Info
How Hybrids Work
Hybrid-electric vehicles (HEVs) combine the benefits of gasoline engines and electric motors and can be configured to obtain different objectives, such as improved fuel economy, increased power, or additional auxiliary power for electronic devices and power tools.
Some of the advanced technologies typically used by hybrids include
- Regenerative Braking. The electric motor applies resistance to the drivetrain causing the wheels to slow down. In return, the energy from the wheels turns the motor, which functions as a generator, converting energy normally wasted during coasting and braking into electricity, which is stored in a battery until needed by the electric motor.
- Electric Motor Drive/Assist. The electric motor provides additional power to assist the engine in accelerating, passing, or hill climbing. This allows a smaller, more efficient engine to be used. In some vehicles, the motor alone provides power for low-speed driving conditions where internal combustion engines are least efficient.
- Automatic Start/Shutoff. Automatically shuts off the engine when the vehicle comes to a stop and restarts it when the accelerator is pressed. This prevents wasted energy from idling.
For fuel economy information on these vehicles, please visit the Compare Side-by-Side section.
Plug-in Hybrid Electric Vehicles (PHEVs) are hybrids with high capacity batteries that can be charged by plugging them into an electrical outlet or charging station. PHEVs can store enough electricity from the power grid to significantly reduce their petroleum consumption under typical driving conditions.
Different Kinds of PHEVs
There are two basic PHEV configurations:
- Series PHEVs, also called Extended Range Electric Vehicles (EREVs). Only the electric motor turns the wheels; the gasoline engine is only used to generate electricity. Series PHEVs can run solely on electricity until the battery needs to be recharged. The gasoline engine will then generate the electricity needed to power the electric motor. For shorter trips, these vehicles might use no gasoline at all.
- Parallel or Blended PHEVs. Both the engine and electric motor are mechanically connected to the wheels, and both propel the vehicle under most driving conditions. Electric-only operation usually occurs only at low speeds.
PHEVs also have different battery capacities, allowing some to travel farther on electricity than others. PHEV fuel economy, like that of electric vehicles and regular hybrids, can be sensitive to driving style, driving conditions, and accessory use.
Benefits and Challenges
Less Petroleum Use. PHEVs are expected to use about 40 to 60 percent less petroleum than conventional vehicles. Since electricity is produced primarily from domestic resources, PHEVs reduce our dependence on oil.
Less Greenhouse Gas (GHG) Emissions. PHEVs are expected to emit less GHG than conventional vehicles, but the amount generated depends partly on the fuel used at electrical power plants—nuclear and hydroelectric plants are cleaner than coal-fired power plants.
Higher Vehicle Costs, Lower Fuel Costs. PHEVs will likely cost $1,000 to $7,000 more than comparable non-plug-in hybrids. Fuel will cost less since electricity is much cheaper than gasoline, but it is unclear whether fuel savings will offset the vehicle cost when PHEVs are first introduced. Federal tax incentives up to $7,500 are currently available for qualifying PHEVs.
Re-charging Takes Time. Re-charging the battery typically takes several hours, but a "quick charge" to 80% capacity may take as little as 30 minutes. However, PHEVs don't have to be plugged in to be driven. They can be fueled solely with gasoline but will not achieve maximum range or fuel economy without charging.
Measuring Fuel Economy. EPA is currently developing a new fuel economy metric for PHEVs that should be finalized by late 2010. This will be a challenge since PHEVs run on both electricity and liquid fuel and it is unclear what percentage of time each will be used during the average driver's daily travel.
Electric vehicles (EVs) are propelled by an electric motor (or motors) powered by rechargeable battery packs. Electric motors have several advantages over internal combustion engines (ICEs):
- Energy efficient. Electric motors convert 75% of the chemical energy from the batteries to power the wheels—internal combustion engines (ICEs) only convert 20% of the energy stored in gasoline.
- Environmentally friendly. EVs emit no tailpipe pollutants, although the power plant producing the electricity may emit them. Electricity from nuclear-, hydro-, solar-, or wind-powered plants causes no air pollutants.
- Performance benefits. Electric motors provide quiet, smooth operation and stronger acceleration and require less maintenance than ICEs.
- Reduce energy dependence. Electricity is a domestic energy source.
EVs face significant battery-related challenges:
- Driving range. Most EVs can only go about 100–200 miles before recharging—gasoline vehicles can go over 300 miles before refueling.
- Recharge time. Fully recharging the battery pack can take 4 to 8 hours. Even a "quick charge" to 80% capacity can take 30 min.
- Battery cost: The large battery packs are expensive and may need to be replaced one or more times.
- Bulk & weight: Battery packs are heavy and take up considerable vehicle space.
However, researchers are working on improved battery technologies to increase driving range and decrease recharging time, weight, and cost. These factors will ultimately determine the future of EVs.
The Nissan Leaf, the City's first two fully electric vehicles added to the fleet
Click Photos Below for Full-Sized Versions