CMU Studies Electric vs. Hybrid Cars

  • Cars that run solely on electric battery power need to refuel at stations like this one. A new study argues hybrids might be a better choice for one-car families. Photo: J.S. Jordan

Do new tax breaks for alternatively fueled vehicles make sense?  New research by Carnegie Mellon University calls that into question.  The Allegheny Front's Jennifer Szweda Jordan interviews researcher and professor Jeremy Michalek. This is part of our alternative-fueled vehicle coverage in advance of our Green Gathering Saturday, Feb. 23. Please join The Allegheny Front pit crew to check out various alternatively fueled vehicles and discuss new technology with experts.

JORDAN: Can you define the study for me a little bit more?

MICHALEK: What we were looking at is what are the total benefits that you can get from plug-in vehicles. We know that there are a number of reasons as to why we would want to switch from gasoline to electic vehicles. One of them is to stop using gasoline, because it's imported and there are some geopolitical strifes associated with it, but the second is to reduce emissions, greenhouse gas emissions for sure, and also air pollution. Air pollution causes respiratory problems, premature death, etc. I didn't expect this to be a large part of the problem but, as we found out from the study, air pollution is still a pretty big part of the problem overall.

JORDAN: How so?

MICHALEK: Well, if you look at the full life-cycle of producing and using a vehicle throughout its life, you gotta account for manufacturing the vehicle, manufacturing the batteries, the emissions that come through the smoke stacks through the factories as well as up streams through the mines. We're getting the original materials and transporting them to the factories, and then of course burning gasoline, refining gasoline, producing that electricity.

So we accounted for all of those things all the way up the supply chain and looked to see how much air pollution is being created, what kind of greenhouse gas emissions, and what kind of gasoline displacement we might be able to expect from each of these vehicles. What we found is a little surprising. You might think that the larger battery vehicles are better, like the purely electric vehicle doesn't use any gasoline at all, so that sounds like that's getting all the way there. The problem is that those vehicles rely on very large battery packs, and there's emissions associated with producing those battery packs. They're also heavy.

JORDAN: How heavy?

MICHALEK: It depends on the vehicle, the larger the battery pack is, the more heavy it is. But it can be like carrying around a bunch of extra people in your car.

JORDAN: What kind of car do you drive?

MICHALEK: I drive a plug-in high powered electric version of the Prius. It's a converted car from several years ago. It's a combination of gas and electric. What we found is if you put a couple miles of battery on the vehicle every time you drive, you use up that electricity, and then you switch to gasoline if you're driving on a longer trip. But if you have a very large battery pack, most of the time you don't drive the full distance of that battery pack. So if I have a 40-mile battery pack, and I take a 20-mile trip, that extra 20 miles of battery is just dead weight, and so it's an investment that I made that I'm not really using on that trip.  Small battery packs do a lot of good for not that much money. The larger batteries cost a lot more money, and the amount of benefit is marginal.

JORDAN: I feel like this makes so much more sense to have both options, so why has anyone historically just had the electric strictly?

MICHALEK: I think there are two reasons why people switch to the all electric. One is because a plug in hybrid seems incremental, and I'm still using gasoline,and if I really do care about the environment shouldn't I get rid of gasoline entirely? I think if you look at it closer, it turns out, if you've got a lot of money, and you like these vehicles, then that's great and go out and buy one, but when we talk about using taxpayer dollars to subsidize, we want to get the most good for the least amount of money. And if we're given an amount of money, we want to do as much good as we can, and we can do a lot more good with these plug in vehicles. They don't cost as much, and they displace a lot more gasoline per dollar spent. The other reason for battery electric vehicles is maybe just the wow factor about battery electric vehicles.

JORDAN: Given that what do you make of the tax credits that were renewed under the fiscal cliff deal for alternative fuel vehicles?

MICHALEK: I think both the federal and state tax credits are pushing for the wrong vehicles. Lawmakers assume that the larger battery packs are better, that we're getting more environmental benefits so we should subsidize them more. I don't think that's true from what we found in our study. Depending on where you get your electricity from, if you get your electricity from an average source in the United States, than the large battery packs can actually be worse.

They can actually have more greenhouse gas emissions and more pollution over the life than a plug-in hybrid electric vehicle, and that's because, again, that plug-in hybrid, couple miles worth of battery on there, you can drive a lot of your local miles on electricity for a small cost and a small amount of battery emissions. When you move to the large battery pack, you do shift more of your miles from gasoline to electricity, but it comes at the cost of a larger and larger battery pack, which means more emissions in manufacturing and more weight to carry around. So I think that both the federal and state policies favoring large battery packs is using more money to produce less environmental benefit.