What's So Special About HEVs?
An Interview with Engineer Keith Wipke

To answer this question, ODYSSEY spoke with Keith Wipke, senior engineer at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) in Golden, CO. He began collecting data on HEVs—hybrid electric vehicles—more than ten years ago. Then, the only hybrids around were built by students for a design competition sponsored by U.S. auto makers and the U.S. Department of Energy. For nine years, he led a team that developed computer models of advanced vehicles, with an emphasis on HEVs.

What does the hybrid combination engine offer over the standard internal combustion engine?

Mainly, flexibility in how you use your gasoline engine. By controlling the engine by computer rather than by your foot, you can do it more efficiently and cleanly. In a Prius, when you put your foot down on the accelerator pedal, the computer tells the engine what to do. You're not directly controlling it. On all other vehicles, when you mash your foot on the pedal, you're directly pulling a wire that's opening the throttle body and letting more air into the engine, which then causes more fuel to go to the engine. So the engine operates all over the map in terms of torque or speed. On the Prius, the engine operates at a very narrow torque and speed, in an efficient, clean region. Except for a true zero-emission vehicle, like a fuel cell or an electric vehicle, it's got the lowest emissions in the book.

Are there any downsides?

Probably the biggest downside at this point is the cost. While I think $20,000 for the new Prius base vehicle isn't a large amount of money to pay for the performance and all the other features, it's probably a $17,000 car if it weren't for the hybrid aspect. So you're still paying a price premium, although what I've seen from Toyota indicates that they'll be able to incrementally reduce the cost of the hybrid aspects—the battery, motor, and generator—such that they'll be able to charge less and still make money.

If you do pay more for your hybrid, can you expect to recover the cost in fuel savings?

I think that you do ultimately recover it if you keep the car long enough. It's probably a 6- to 8-year payback period, which is a long time for something like that. Certainly on a month-to-month basis you feel the impact of not spending so much on gasoline, and you probably forget the fact that you paid more originally. The fact that the new vehicle gets 650 miles per tank is a continuing mental encouragement. Forget the economic basis—that's a time-saver. That was one of the biggest things that GM [General Motors] found from their surveys of people when they were making electric vehicles a decade ago: One of the things that people really liked was not having to go to the gas station. Thinking about driving across the country, I don't know anybody who can drive 650 miles without stopping to go to the bathroom, but at the same time, it's nice to be able to stop anywhere to go to the bathroom and not have to go to a gas station to do it.

How many drivers would have to switch to hybrids to make a significant reduction in our oil imports?

Certainly hybrids can make a big dent in fuel consumption, because they can reach out across such a broad population. We did do some studies early on at NREL and found that hybrids can actually save a lot more fuel than electric vehicles, because almost everybody can buy and drive a hybrid for their needs, whereas the number of people who could be comfortable driving a vehicle that has an 80- or 100-mile range is small. If you can make hybrids such that they can go into every vehicle that's on the road now, which is what Toyota plans on doing, that will displace a large amount of fuel. And it will do it without causing a major shift in the market or regulations. Basically, people will buy the vehicles because they want them, because they're getting something better out of those vehicles.


  • emission: A substance discharged into the air, especially by an internal combustion engine.
  • hybrid: Something of mixed origin or composition.
  • increment: One of a series of regular additions.

Back to Top


  1. How do HEVs help conservation efforts?
  2. Why would the cost of an HEV and the savings associated with driving an HEV affect a person's decision to buy an HEV?
  3. When you are old enough to drive and buy a car, would you buy an HEV? Why or why not? Write a couple of sentences explaining your answer.