Electric Vehicle Types
For over 100 years, the predominant energy of choice for cars has been petroleum, fueling the internal combustion engine. Today, electric vehicles are being designed to augment internal combustion, or eliminate the need for it altogether.
Hybrid and electric vehicles may include a battery for energy storage, electric motor for propulsion, a generator, a mechanical transmission system and/or power control system. These components are brought together in different ways by different systems. There are four basic kinds of cars:
1. Hybrid Electric Vehicles
The hybrid electric vehicle uses a small electric battery to supplement a standard internal combustion engine and increase fuel efficiency by about 25 percent over competing light-duty vehicles.
The battery minimizes idling, and enhances the vehicle's ability to stop and go—important in city driving. The electric battery can accelerate the car to about 40 mph, and then the combustion engine takes over.
The battery is recharged by the gasoline engine and by regenerative braking, in which energy that would otherwise be lost as heat in the break pads is instead transformed into electricity to fuel the battery. The Ford Fusion Hybrid and the Toyota Prius are examples of this type of hybrid.
2. Plug-in Hybrid Vehicle
The plug-in hybrid is also a dual-fuel car with an electric motor and a combustion engine. However, it has a larger battery pack that is charged directly from the power grid, increasing the amount of electric power available for propulsion.
This larger battery usually supplements an internal combustion engine smaller than those used in hybrid or conventional vehicles. Toyota began selling a Prius plug-in hybrid for the U.S. market in February 2012, though kits to convert other cars into plug-in hybrids were available before that.
These hybrids run on electricity up to 40 mph, when the combustion engine kicks in. That means that many Valley dwellers can commute around town on electricity, but need to engage the combustion engine in order to safely navigate the interstates.
The batteries in these cars can be recharged by the gas engine, regenerative braking and by plugging the car in at home during off-peak hours.
3. Extended-Range Vehicles
An extended-range electric vehicle uses an internal combustion engine to power an electric generator that charges the battery system in a linear process—the engine powers a generator, which in turn charges the battery.
Unlike hybrid electric and plug-in hybrids, only the electric motor powers the wheels of an extended-range car. The internal combustion engine only charges the batteries.
The General Motors Volt, which went on sale in the U.S. in late 2010, is an extended-range car with an electric-only range of about 40 miles.
4. Battery Electric Vehicle (BEV)
Battery electric vehicles are 100 percent electric. They have no internal combustion engine and must be plugged into the electric power grid for recharging. To accommodate a range of 80-plus miles per charge, electric-only vehicles require larger batteries—from 18 kilowatts-hours to more than 35 kilowatt-hours.
To more quickly recharge these vehicles at night when rates are low, homes require special outlets to be installed that provide 240 volts or higher.
Nissan began U.S. sales of its 100 percent battery vehicle, the LEAF, in late 2010. TVA and the state of Tennessee helped develop a launch market for this vehicle.
The EV Project
TVA is involved in a multi-partner initiative — the EV Project — the largest deployment of electric vehicles and charging infrastructure in history.
Building the Stations
The TVA SMART Station deployment, powered in part by solar energy, will supplement the network of charging stations developed by ECOtality North America and regional stakeholders across Knoxville, Nashville and Chattanooga, TN.
The design for the first prototype, known as the Smart Modal Area Recharge Terminal, or SMART station, features power generation by solar photovoltaic panels, stationary battery storage of power and key elements of smart grid technology.
TVA and its partners are making the SMART station design public at no charge so that communities and developers across the country can take advantage of best practices developed there.