TransForum Vol. 7, No. 1

Argonne Leading DOE's Plug-In Hybrid Technology Evaluation Effort

The U.S. Department of Energy’s (DOE's) FreedomCAR and Vehicle Technologies Program recently designated Argonne National Laboratory as DOE's lead national laboratory for the simulation, validation, and laboratory evaluation of plug-in hybrid electric vehicles (PHEVs) and the advanced technologies required for these vehicles.

A plug-in hybrid electric vehicle is similar to the hybrid electric vehicles (HEVs) on the market today, but with a larger battery that is charged both by the vehicle's gasoline engine and from plugging into a standard 110 V electrical outlet for a few hours each day. PHEVs and HEVs both use battery-powered motors and gasoline-powered engines for high fuel efficiency, but PHEVs can further reduce fuel usage by employing electrical energy captured through daily charging.

Argonne experts estimate that a PHEV could get more than 100 miles per gallon while the vehicle runs primarily on the battery — compared to the 30 to 55 miles per gallon that most of today's HEVs achieve — at a charging cost that's equivalent to roughly $1 a gallon. Commuters who drive less than 20 miles a day might be able to drive a PHEV exclusively with its electric motor for their daily commutes.

While the PHEV technology shows promise, many broad energy and environmental considerations must be examined before PHEVs become widely available. For example, while a PHEV might cost less to drive than a gasoline-powered vehicle, it would draw power from the electrical grid when charging. Virtually all electricity in the United States today comes from domestic energy sources, and in some areas, much of that electricity comes from coal-burning power-generation plants. The energy needed to extract and transport the coal, as well as the environmental considerations associated with burning the coal, are all part of the overall cost of using plug-in technology. These issues could decrease in importance as the amount of renewable energy in the electricity mix increases. Other significant technical barriers to commercialization of PHEV technology include cost, battery size and performance, durability, and safety.

Cost

PHEVs require additional, expensive components — such as very large, heavy, and costly batteries — to provide adequate vehicle range. Also, power electronics must become smaller, simpler, and less expensive. The U.S. Department of Energy has determined that to be commercially viable, a hybrid technology vehicle must repay its extra upfront cost in the form of fuel savings within three years of the initial purchase in order to achieve widespread acceptance.

Battery Size and Performance

PHEV batteries must be compact in size, and offer high energy, large storage capacity, and the ability to support both deep and shallow discharge/charge cycles. With today's technology, a battery that's powerful and durable enough to power a PHEV’s electric motor takes up more space than many vehicle makers or consumers are willing to sacrifice. In addition to the space occupied by the battery itself, there is also space on top of and around the battery that for safety reasons cannot be used. Old batteries must be recycled, and no one yet knows how much that recycling will cost on a per-vehicle basis once all transport, processing, and disposal costs are considered.

Durability

If you own any of today's high-tech rechargeable-battery-powered devices, such as MP3 players, PDAs or cell phones, you probably understand this problem firsthand. A battery small enough to meet the device's form factor and power requirements requires frequent recharging, and over time, it loses its ability to take and hold a new charge. Eventually, the battery must be replaced. In a car, however, consumers would expect the battery to last the life of the vehicle.

Safety

Any battery is potentially unsafe when mishandled or subjected to trauma such as physical blows, extremely high temperatures, or fire. Consequently, a vehicle that is safe under normal conditions requires a great deal of testing to determine its safety in a crash or fire. New battery technologies will require extensive testing before they are deemed suitable for in-vehicle use. Emergency responders must also learn how to handle new vehicle battery technologies safely in the event of a crash or fire.

To address these issues and others, the U.S. Department of Energy's FreedomCAR and Vehicle Technologies Program is funding research in a variety of technical areas specific to PHEVs, including:

• Hardware-in-the-loop analysis
• Modeling & simulation
• Research and development for critical components such as batteries, motors and power electronics
• Component/subsystem testing and validation
• System and interface control development
• Vehicle testing and validation

Working together with researchers from Idaho National Laboratory, Argonne researchers are focusing their efforts in all of these areas to assess the technical, economic, and environmental viability of PHEV technology.

What's a Hybrid Electric Vehicle?

A hybrid is any vehicle that uses two or more sources of power—in today's HEVs, the two sources are electricity (from batteries) and mechanical power (from a small internal combustion engine). HEVs combine very low emissions with the power and range of gasoline vehicles. They also offer up to 30 miles more per gallon, perform as well as or better than, and are just as safe as any comparable gasoline-powered car.

How Does it Work?

When engine demand is low, such as when starting, traveling at a light load, or stopping, an HEV is driven only by its electric motor, using battery power. During normal travel, the gasoline engine engages as needed to drive the wheels and/or recharge the battery.

At full acceleration, the battery adds its power to the mix, which provides a very smooth, powerful response. When decelerating or braking, the regenerative braking system acts as a generator to help recharge the battery.

The engine shuts off when the car is idling or if engine demand is low. The gasoline engine runs only as needed to recharge the battery or run the air conditioner, which is why an HEV never has to be plugged in for recharging.

The HEV of the Future

In the future, an advanced hybrid, or plug-in hybrid electric vehicle, could be plugged in at night, using off-peak electricity, to "top off" the car's higher energy content lithium-ion batteries. This would extend the car's range and offer more than 100 miles per gallon of gasoline.

What is a PHEV and How Does it Work?

A plug-in hybrid electric vehicle (PHEV) is part electric vehicle and part gasoline vehicle. The difference between a PHEV and the hybrid electric vehicles (HEVs) you can buy today lies in how they charge their batteries.

A PHEV is similar to an HEV, but it has a larger battery that can be fully charged by plugging into a standard 110 V electrical outlet for a few hours each day. When the battery runs low, the vehicle acts like today's conventional hybrids with high fuel economy, but without using any more energy originating from "the plug."

March 2, 2007