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Transportation Technology R&D Center |
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Modeling, Simulation & Software Plug-In Hybrid Electric Vehicles Transportation Research and Analysis Computing Center |
Why Don't We Have Plug-in Hybrids Today?
While plug-in hybrid electric vehicles (PHEVs) are a promising vehicle technology, there are many broad energy and environmental considerations that must be examined before they become widely available. For example, while a PHEV might be less costly for the consumer to drive than a gasoline-powered vehicle, it would draw power from the electrical grid when charging. In many parts of the United States , much of that electricity would likely be generated by coal-burning power generation plants. The costs 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 decrease in importance as the amount of renewable energy in the electricity mix increases. There is also the question of how used batteries will be recycled, and how much that recycling will cost on a per-vehicle basis once all transport, processing, and disposal costs are considered. Significant technical barriers must be also overcome before plug-in hybrid electric vehicles are available at your local car dealer. These include:
Let's look at each of these reasons separately. CostPHEVs require additional and very expensive components. Very large, heavy, and costly batteries are required to provide the range of miles, or electricity. Also, power electronics need to be reduced in complexity, size, and cost. 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. Battery Size/PerformanceThe goals for a PHEV battery are compact size, high energy, high storage capacity, and the ability to support both deep and shallow discharge/charge cycles. With the battery technologies available today, a battery that's powerful and durable enough to power a PHEV's electric motor is big — taking up more room 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 can’t be used for design and safety reasons. Fortunately, as battery technology evolves, these issues are likely to diminish. DurabilityChances are, if you own or have tried any of today's high-tech rechargeable-battery-powered devices such as MP3 players, PDAs, or cell phones, you understand this problem firsthand. A battery small enough to meet the device’s form factor AND power needs must be recharged frequently, and over time, it loses its charge capacity. That means that as the battery ages, you get less power from a charge then you did when the battery was new. Eventually, the battery will need to be replaced. In a car, however, you would expect the battery to last the life of the vehicle. SafetyAll batteries present safety considerations when they are mishandled or subjected to trauma such as physical blows, extreme high-temperature conditions, or fire. Even though a vehicle itself is safe, a great deal of testing is required to determine its safety in the event of a crash or a fire. As new battery technologies are developed, they will require extensive testing before they are deemed suitable for in-vehicle use. Emergency responders must also learn how to safely handle new vehicle battery technologies in the event of a crash and/or fire. To address these issues and others, the U.S. Department of Energy’s Vehicle Technologies Program is funding research in a variety of technical areas specific to PHEVs, including:
More Information
December 2006 |
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