Plug-In Hybrids Hybrid Synergy View Newsletter Winter 2007
The idea seems simple enough: Just add a cord and a plug to a Prius so you can charge its battery on ordinary household electric current overnight. Then, use only the battery power to make the short round-trips to work, school or the store. That would save lots of gas, and the charging could be done mainly at night, when utility rates are cheaper. When driving longer distances, the engine kicks in and the vehicle operates on gasoline, much like today’s Hybrid Synergy Drive® vehicles. This inspiring idea has caught the public’s attention as an energy-security measure that uses domestic and potentially renewable resources. Not surprisingly, it has prompted questions to automakers about when the first commercial plug-in hybrid can be expected.
As the leading maker of hybrid vehicles, responsible for three out of four sold in the United States last year, Toyota receives many of these questions. Toyota believes plug-in hybrid vehicles are an appealing technology offering possibilities for energy diversity. Depending on electric power sources, they may offer reductions in both emissions and fuel consumption. Reaching this vision, however, will require breakthroughs in battery technology, including capacity, durability and cost. At present, plug-in hybrid vehicles are not commercially feasible. It’s about batteries An earlier edition of Hybrid Synergy View pointed out that much of the “magic” that makes hybrid vehicles work involves high-voltage battery technology.
Bill Reinert, national manager in the Advanced Technology Group at Toyota Motor Sales, U.S.A., says, “It all comes back to the battery. If you want to run longer and farther on electric power alone, it means a bigger battery. It means charging a battery more fully and discharging it more completely. And, it means provisions for cooling or ventilation in order to give the batteries longer life.” “You have to decide what you want and what you’re willing to give up,” says Reinert. “A bigger battery might mean less space for passengers or luggage, for example. And a much more costly battery could mean a very long payback period for the investment in a fuel-saving plug-in system.” So, Reinert concludes that a great deal of work is being done in storage battery technology, but much more remains. Designing a system Doug Coleman, advanced technology vehicle manager in Toyota’s Vehicle Operations Group, says a system that allows the driver to stay in electric mode is referred to as having AER, or “all-electric range.” He explains that this kind of system may not be the first one that reaches commercial production. “To achieve the acceleration, highway speeds and hill-climbing abilities most motorists demand,” Coleman says, “an AER system might need not only a more powerful battery but a bigger motor and related electronics as well. This could make it uneconomical to produce — too costly for mass distribution.” “It’s possible,” he adds, “that a plug-in hybrid might use a blended system of plug-in battery power and engine power that doesn’t force the engine to be shut down. A car like that could use a less powerful motor and battery because its computer would engage the engine when more power is needed, much like a Prius does today.” The blended approach, Coleman explains, could give the vehicle owner the fuel savings and the emissions reduction he or she is looking for without a lot of extra cost. Other design challenges Bill Reinert believes an effective plug-in hybrid system would not only have to be commercially practical, it would also need to be so reliable as to be warranted, like present-day Toyota hybrids, for up to 10 years or 150,000 miles. This, he states, would be especially challenging if the batteries were more deeply discharged, which could shorten battery life. He says a global company like Toyota must also make its system compatible with the variety of household electric currents and different electric receptacles and connections used worldwide. No magic bullet yet Reinert concludes that none of the plug-in hybrid systems thus far demonstrated by scientists and entrepreneurs meet all the challenges of commercial acceptability. Those challenges, he says, include size, weight, performance, durability and cost. But if these can be overcome, there may well be a bright future for the plug-in hybrid.