Commentary—

Hybrid Cars: The Best Is Yet To Come

By John M. Evans

Nancy Crevier wrote an entertaining ode to her 2006 Toyota Prius in the July 27 issue of The Bee. I would like to build on that column from an engineer’s perspective with a look ahead at the next generation “plug-in hybrids” that will begin with a 2009 model of the Prius.

 How does the current Prius work? It has an electric motor that is in series with the gasoline engine in the drive train so the electric motor adds power to the gas engine when peak power is needed for acceleration or running uphill. That extra power comes from a large pack of batteries. This allows use of a smaller, more fuel-efficient gasoline engine that provides only average power, not peak power.

An electric motor is also a generator of electricity: apply voltage and it turns the shaft; turn the shaft and it generates voltage. So the motor can be used as a generator to recharge the batteries, driven by the gasoline engine whenever full power is not needed and also recapturing energy during braking.

The exciting next step is the “plug-in” version, which will recharge the battery pack from a 110 volt outlet. This can be done at night during off-peak hours for electricity demand. Starting with a fully charged battery pack will allow something like the first 20 miles of driving to be on battery power only. The advantages? The mileage rating will be something like 100 mpg and energy from the electric power grid is equivalent to gasoline at about $1 per gallon, so the plug-ins will be very cost-effective. From an environmental standpoint, there is zero pollution when the car is driven solely on electric power. Also, dealing with pollution and CO2 emissions at a single source, the power plant, is far easier than at thousands of sources in individual cars.

Toyota should be congratulated for deciding to use nickel metal hydride (NiMH) batteries for their plug-in, the same type used in the current Prius. These have a good proven track record: Toyota warrants the batteries of a Prius for 150,000 miles or ten years. The US car companies are holding out for a newer type of battery, the lithium ion battery, which has twice the energy density (stored energy per pound) of NiMH batteries. Lithium ion batteries are used in laptop computers but have not been used in large power applications to date. I feel there are significant questions as to the long-term safety and durability of large-scale lithium batteries, so I believe Toyota’s decision to use proven technology is a good one.

The final step in fuel efficiency will be running the engine on E85 fuel when ethanol from cellulose is available in large quantities and low cost, probably in about ten years time. A future plug-in hybrid rated at 150 mpg will get 1,000 miles per gallon of gasoline when using E85 fuel. I believe this is a primary solution to the coming oil crisis, not fuel cells and hydrogen.

Two questions arise. First, widespread use of hybrids and pure electrics with large NiMH and Li ion battery packs raises an issue of recycling and disposal of spent batteries in a safe and environmentally friendly way. This will become an issue that needs attention.

Second, there is a question as to road taxes when driving on a battery charge from the grid. We pay road taxes on gasoline. Should we have a comparable tax on electricity used to recharge electrics and hybrids? Governor Rell and the legislature will need to consider this in the very near future.

Interesting historical note: The US car companies were ahead in hybrid technology in the 1990s. Ironically, the Prius is a result of the Japanese car companies being frightened by that American lead. In 1993, the Clinton administration started a program to aid the American auto industry called Partnership for a New Generation of Vehicles (PNGV). The government provided research funds and the car companies decided how to invest those funds in precompetitive research. They focused on diesel hybrid drives and all three US car companies built prototypes that got over 70 mpg. The car companies pulled the plug on this program in 2001, saying that hydrogen and fuel cells were the key technologies for the future, not diesels and hybrids, and the Bush administration started a new program, called Freedom CAR, to work on hydrogen fueled vehicles.

Meanwhile the Japanese car companies, worried about the PNGV program, got the Japanese government to provide comparable research funding and this resulted in the Toyota Prius and the Honda Insight. The US car companies did introduce limited production of hybrid technologies for light trucks and SUVs, but the increase in gas mileage has been modest and sales have been minimal while the Prius, with a doubling of fuel efficiency and elegant styling, has been a huge success.

(John M. Evans has a PhD in physics and has worked for the National Institute of Standards and Technology and for HelpMate Robotics in Danbury. He is a resident of Newtown.)