By 
This week David asks “how much more energy efficient does a new car have to be to make up for the energy of production vs a used car? For example, if someone was considering buying a used car that gets 18 mpg vs. a new car that gets 30 mpg. At what point in driving would that increase in mpg make up for the energy of production of the new vehicle?” Read on to find the answer in this week’s AskPablo.
The Argonne National Lab has done a great job in analyzing the material intensity and energy consumption in manufacturing vehicles and vehicle fuels. Their work is packaged in the GREET 1.7 and 2.7 models (Excel-based and available at: http://www.transportation.anl.gov/software/GREET/). According to the assumptions in their model the average conventional internal combustion engine vehicle (ICEV) is made up of 61.7% steel, 11.1% iron, 6.9% aluminum, 1.9% copper/brass, 2.9% glass, and around 13.6% plastic/rubber. This data will help us determine the energy required to produce a vehicle. We will also have to look at the energy used in operating a vehicle. To help us along in our analysis we will look back at AskPablo: Lighten the Load to find the relationship between vehicle weight and fuel efficiency.
According to the GREET model it takes 100.391 mmBTU (million BTU) to make the vehicle, batteries, and fluids in an average 3,201 pound vehicle. This comes out to 31,362 BTU/lb. The obvious lesson in this is that heavier vehicles require more energy to make than lighter ones, in general. There has been a study circulating that states that hybrids are more environmentally damaging than Hummers because of the battery production but this has been widely disputed. According to the GREET model a Hybrid Electric Vehicle (HEV) that weighs 2,632 pounds requires 101.726 mmBTU to make, or 38,650 BTU/lb. As we will see, this small difference in production energy becomes negligible when you factor in the increased fuel efficiency.
Using the GREET assumptions I will compare several vehicles, a Hummer H2, a Toyota Prius, and the Toyota Highlander (standard and hybrid). I will use the vehicle’s published curb weight to determine the energy used in manufacturing, based on the mmBTU/lb factors above and I will use the average MPG (city and highway) to estimate fuel usage over a 160,000 mile lifespan. The energy required to manufacture the vehicles is:
- Hummer H2: 200.717 mmBTU
- Toyota Prius: 113.322 mmBTU
- Toyota Highlander: 107.133 mmBTU
- Toyota Highlander Hybrid: 155.18 mmBTU
Gasoline contains 113,500 BTU (0.1134 mmBTU) per gallon. By dividing the expected lifespan of a vehicle (160,000) by its average MPG we can determine the gallons of gasoline used over that lifetime. We can also multiply this by the energy content of the fuel to get the total energy used. The gallons used during a 160,000 mile lifespan and the energy contained therein is:
- Hummer H2: 13,913 gallons ($44,800 at today’s prices!), 1579.13 mmBTU
- Toyota Prius: 2,883 gallons, 327.207 mmBTU
- Toyota Highlander: 6,400, 726.4 mmBTU
- Toyota Highlander Hybrid: 5,424, 615.593 mmBTU
So, in comparison, 89% of the energy consumed by a Hummer H2 is in burning fuel, whereas the Toyota Prius uses 74% of total energy on burning fuel. This means that, in relation to weight, the Prius requires more energy to manufacture, but the Hummer uses far more energy to operate. What we also learn (click on the graph to enlarge) is that a Hummer H2 uses more energy in the first 24,000 miles (roughly 2 years) than the Prius will in its entire lifetime.
Here is my advice, David: Continuing to drive an older car with poor fuel economy is less environmentally friendly than getting a new car that gets drastically better fuel economy. You can take my factors above and calculate the exact energy use for your old vehicle and a new vehicle to see the comparison. Keep in mind that these results are for the energy used, not the carbon dioxide emissions, but the two are highly correlated since most of our energy comes from fossil fuels.
Pablo Päster, MBA
Sustainability Engineer
Comments
March 14, 2008 at 0:58 am PDT | dimdim writes:
Toyota, for example, is well respected in the industry for its efficient construction and distribution processes, which have a lower environmental impact than those used by some other manufacturers.
March 27, 2008 at 22:53 pm PDT | Anonymous writes:
Assuming the 100MMBTU (31826 kWh) figure for making a car is correct, then based on an average European electricity mix of Coal, Oil, Gas, Hydro, Nuclear, Wind, Solar that generates around 600g CO2 / kWh (whether it is 500 or 750 does not matter too much in this analysis) to produce your vehicle 19 tonnes of CO2 are emitted. A modern new small diesel car producing 120g C02/km needs to drive 159000 km to produce the same CO2. So even if your old car does a really poor 240g C02/km then if you can drive it 100000miles more before it produces more C02 than buying a new car. Sure if the old car does not have a particle filter, catalytic converter etc, it will still produce more conventional “pollution”. But in terms of current emphasis on C02 I would disagree that trading your old car in is more “environmentally friendly”. Like another contributor noted we live in a throw away society mainly because the value of a persons work is so much more valued than a natural resource – and that is wrong. People are replaceable!
By the way even a sporty electric car using 0.2kWh/km of electricity is going to emit during running 120g C02/km. The problem will always exist with electricity unless you have a truly renewable prime source.
March 30, 2008 at 13:32 pm PDT | Anonymous writes:
Making a diesel engine today is almost as expensive as making a turbo gasoline engine, or barely 500$ more than a regular gas engine. Here in europe, most cars today are diesel ones.
As for how green diesels are.. we call them “squids”, because when you push them hard (traffic lights..) they release a small black cloud.
Some people complain saying that new luxury hybrids are not “green”. They were not designed to be green, but incredibly smooth.. and they certainly are.
June 18, 2008 at 17:57 pm PDT | geeaea writes:
(we’re hoping to be able to hold out for a plug-in hybrid, since we recently put solar panels on our roof!),
Lady ..to even say that you’re wasting more energy than 80% of the population. Move out of the McMansion and buy a rowhome/townhouse ..give up the ipods for the kids and make them learn some life skills.
June 18, 2008 at 17:58 pm PDT | geeaea writes:
(we’re hoping to be able to hold out for a plug-in hybrid, since we recently put solar panels on our roof!),
Lady ..to even say that you’re wasting more energy than 80% of the population. Move out of the McMansion and buy a rowhome/townhouse ..give up the ipods for the kids and make them learn some life skills.
Nature’s way of saying you make way too much money
July 11, 2008 at 12:19 pm PDT | wb writes:
I am just going to buy a $40,000 hummer h2 for approximately $21,000. Lets see… If I am spending $4000 a year on gas, but I am saving roughly $18,000-$20,000 off of the initial price, and I keep the SUV for about 5 years…
I still come out saving roughly $10,000. How is this?? Well… considering your average FUN to drive car (not economy car) gets about 23 mpg or less, the fact that I am saving twenty grand off of my luxury vehicle outweighs the savings in gas. Besides, my weekend car gets 27 mpg, does 0-60 in 4.5 seconds, has a 13.2 second quarter mile, and handles better than any car on the road. Can you say screw an economy car anyone? Too bad there aren’t more car companies that crank out cars with those numbers. Anyways, I am going to take full advantage of this gas scare and get a hummer and SAVE money!
July 28, 2008 at 7:19 am PDT | brazos2 writes:
And don’t forget insurance rates. For example, to insure a new Civic cost more than a new Ford truck. Appears it’s safety rating is the pits.
And diesel is NOT imported, all made right here in the USA,. So why is it’s cost so much higher than gas fuel?
August 05, 2008 at 8:56 am PDT | Kristina writes:
I didn’t have the energy to read all of these comments, but I did the analysis myself considering USED cars (why did the author even mention used cars since he did the analysis for only new cars? And a Hummer and two SUVs vs. a hybrid… hmm, fair comparison much?). The proper way to do the analysis is to consider marginal energy used in a new hybrid vs. a used car for the remainder of their lifespans. And when you consider a relatively middle-of-the-road used car with 50K miles on it already that gets about 30 mpg, then it will use less energy over the remainder of its lifespan (160K miles) than the hybrid. When you consider older cars that have many more miles on them, the difference can be staggering. So if the main conclusion here was: ‘don’t buy a new hummer or SUV, buy a hybrid’ then that’s fine. But he is completely wrong to say ‘buy a new hybrid over a used car.’ He gives you all of the relevant data in the article, so you can do this analysis yourself for whichever used car you’d like to compare a hybrid to.
September 21, 2008 at 16:27 pm PDT | J Denmark writes:
Faulty calculation. The advanced metals and batteries in a Hybrid car uses MUCH more energy per pound than the more simple metals in a Hummer.
Actually calculations show that a Hummer is more eco-friendly than an Toyota Prius because of that. So simply using their weight for your calculation completely misses that point.
November 11, 2008 at 13:59 pm PST | Shawn writes:
The internet is serving its purpose as a way for people to get their untruths published. It’s sad that unlike on wikipedia, we can’t delete the totally mistaken comments. To spread lies, you used to have to be a media magnate, a Citizen Kane, now you can just be:
J Denmark doesn’t know how to make steel for a Hummer apparently, or consider all the chromium and nickel in its wheels, bumper, etc. Hint: steel, which the Hummer has in spades, has lots of chromium in it, and some steel alloys (though not the body-steel) have lots of nickel in them. Much of the steel in both cars is made from recycled scrap. Guess which car uses a lot less?
Josh calls cargo ships and trains “hugely inefficient.” About the only more efficient vehicles are bicycles, pound for pound. How dare he lump ships and trains in with planes, which are so inefficient…it’s obvious that Toyota doesn’t use them to ship Prius parts or any significant parts for any car. This study is not BS, it is scientific, unlike Josh’s comment.
Unscientific statements like “My car is 20 years old and has 400000 miles on it, so this whole argument is wrong” are made by people who just don’t understand statistics.
Kudos to people like Loren who understand the subtleties of the inferences…That it depends what the new Prius is replacing, and what happens to the replacement, and to the money of each affected party.
All those people who make the “keep the junker” arguments, consider an easier to understand refutation: compact fluorescent light bulbs. Would you wait until your a-lamps burn out to replace them, or immediately replace them? If you wait, you are wasting your money, carbon emissions, and your ability to think beyond today. Run your analysis over a long enough time period, and you see that early adopters should be patted on the back, not denigrated. Of course, those already driving a better-than-average car, like a compact, should be allowed to be last in line, the worse cars getting replaced first…but, eventually, improve. Don’t defend your little 1990 clunkers forever, please.
If you think a Prius mileage claims are overhyped, you haven’t seen side-by-side comparisons in the kind of stoplight driving so many people do. C’mon people, learn a little science. You must control variables if you have too many to make sense.
But don’t worry, even posters with whom I mostly agree have made errors here:
“If the average price of a new vehicle is $30,000, that means that at least half of the buyers can afford it.” Um, no…half of the buyers can afford the “median” price, not the “average price.” The median price is different (much lower, I think) than the average, since more cheap cars are sold than luxury cars. (Corrected by another poster July 18, 2007, but our arguments not accepted by orig poster.)
Also, the batteries get recycled when you swap them on your Prius. It should also be noted that much of the Hummer gets recycled too, when you take it off the road (so take it off today!). Kudos to Darrel for noting the complexity of materials sourcing.
Comments like “I don’t look like a retard driving it” show how people allow irrational arguments to enter here.
Prius-owner-Wannabee, a Hummer *does* have a pollution control, at least one catalytic converter.
November 11, 2008 at 14:04 pm PST | Shawn writes:
Oh, and GREET is now at:
http://www.transportation.anl.gov/modeling_simulation/GREET/index.html
February 02, 2009 at 4:11 am PST | Anonymous writes:
Should not the energy cost of recycling these vehicles also be taken into account.
How much more energy does it take to recycle the much larger batteries in the hybrib? Also can all of the battery pack be economically recycled and used again?
I also wonder if the argument matters anyway, seeing as hydroden power is on the way?
March 16, 2009 at 6:18 am PDT | Brittany Perry writes:
I would like to know how fuel efficiency from a hummer effects our planet today? and I would like to know if it effected the earth when they first came out
April 01, 2009 at 22:29 pm PDT | Erin writes:
I am buying my first car. I can easily spend $15K, but may be able to stretch and get a new car for $17K. If I could afford a hybrid or had the dedication to maintain a car run on veggie oil, I’d do it. But these are a few cars I’ve seen in my price range: a 2006 VW Jetta ($14K), a 2007 Honda Civic Coupe ($13K), or a new 2009 Civic Coupe ($17.5). Which is the best choice for the environment? They all have similar gas milage, but the used cars have already been produced, thus is buying a used car a type recycling?
April 01, 2009 at 23:05 pm PDT | Erin writes:
Correction: the Jetta’s fuel efficiency is not as good. What about a Ford Focus or the Ford Fusion? I’m open to suggestions as well. What would you do?
April 03, 2009 at 12:27 pm PDT | Krusty writes:
Alright everyone. Enough with the sweeping generalizations, please. I just bought a used 06 Prius. I had an 06 passat. I am not a sanctimonious jerk, nor am I a bleeding heart socialist liberal. I’m a moderate republican, and I’ve been in the military for almost 16 years.
I bought the Prius because:
1. I think our nation has better things to spend its money on than pissing CO2 into the air that came from American $ spent to line the pockets oil producing foreign countries.
2. It’s fun to drive! Sitting through rush hour traffic is a lot less of a drag when you make a challenge of getting optimal performance out of the hybrid system. So far, I’m averaging 53 MPG and recently made my 18 mile commute at 60.2 MPG. – and I don’t drive like my grandmother, either.
3. It’s cheap to maintain. Maintenance cost per mile is on the order of .04 per mile, compared to .09-.12 for my Passat.
Here’s the down-side. Yeah, it’s ugly! In the month I’ve owned this car, I’ve been nearly run off the road twice…both times by angry dudes in big pickup trucks. That, along with the comments in this this blog highlight a couple of facts:
1. For some reason, people seem to behave differently when driving their cars, compared to the way they would treat someone face to face.
2. People are afraid of change, and they fear that this latest trend toward green stuff will cramp our style.
Why can’t we have it both ways? GM, Ford, Dodge, How about making big pickup trucks that get 100 MPG?
WTF? It’s a free country. You drive your gas guzzler – it’s your choice. I drive my prius. That’s mine. Fortunately, we all still have that choice.
August 04, 2009 at 8:55 am PDT | christo930 writes:
Nobody who drives a humvee is going to trade it in for a Prius. The much more likely gas savings is so small that is negated by the upfront energy usage of a new car. People who are driving big cars usually are doing so because they need one. I am 6′4″ 230 lbs and I seriously doubt I could even fit in a Prius. I would trade in my mid size for another midsize.