Hummer vs Prius: the facts
For a long time now, there’s been something of a myth circulating the Web that claims that a Hummer is actually more ecologically friendly than a Prius. The claim is based on a study by CNW Marketing Research that supposedly takes into account the environmental impact of the manufacturing processes of each vehicle in order to evaluate their lifetime energy consumptions.
The study concludes that the energy-intensive manufacturing and recycling process of the Prius outweighs any environmental benefits gained through its low fuel consumption, and that a Hummer, thanks to its traditional construction and materials consumes less energy in its lifetime.
Toyota responded soon afterwards, saying that the study overemphasised the energy involved in manufacturing. They argued that most of a vehicle’s lifetime energy consumption occurs during driving. It’s fairly obvious that Toyota would want to defend the Prius, as that car bestows the marque with an awful lot of green cred. The question is: were Toyota’s claims accurate?
The Argonne National Lab spent a lot of time analyzing the material intensity and energy consumption in the manufacturing of vehicles and fuels. The fruits of their labour are the GREET models, which can be found here.
According to the GREET model, the average conventional internal combustion engine vehicle (ICEV) is comprised of 61.7% steel, 11.1% iron, 6.9% aluminum, 1.9% copper/brass, 2.9% glass, and around 13.6% plastic/rubber.
By calculating the energy required to manufacture a specific mass of each material type, and then factoring the above percentages into the overall mass of a vehicle, we can get a reasonable estimate of the amount of energy that went into producing the vehicle.
The GREET model thus states that an average, 1451kg car requires 100.391 mmBTU (million BTU) of energy to make; including the vehicle itself, the batteries, and fluids. This comes out to 69142 BTU/kg. Clearly then, more energy is needed to make heavy vehicles than light ones.
Additionally, the GREET model makes provision for a Hybrid Electric Vehicles (HEVs). According to GREET, an 1194kg hybrid needs 101.726 mmBTU to make, or 85209 BTU/kg.
So let’s compare vehicles.
A Hummer H2 weighs 2903 kg, the “baby” Hummer H3 weighs 2132 kg and a Prius weighs 1325 kg. Plugging in the respective values for ICEVs and HEVs from the GREET model gives us the following values:
Hummer H2: 200.719 mmBTU
Hummer H3: 147.410 mmBTU
Toyota Prius: 112.910 mmBTU
Hmm… looks like the Prius is already ahead, and that’s before we factor in fuel consumption.
Let’s assume that each of these vehicles travels 250 000km in its lifetime. We can now easily work out how much fuel each will consume, based on its average combined cycle fuel consumption figures. I will use the manufacturers’ claimed figures for this calculation. The final step here is to multiply the number of litres of fuel each vehicle will use over 250 000km by the amount of energy stored in the petrol itself: 29983.53 BTU/litre. The energy expended on burning fuel is thus:
Hummer H2: 1536.76 mm BTU
Hummer H3: 1030.981 mmBTU
Toyota Prius: 321.247 mmBTU
Adding up the manufacturing and fuel-usage figures gives us the following totals:
Hummer H2: 1737.479 mmBTU
Hummer H3: 1178.392 mmBTU
Toyota Prius: 434.158 mmBTU
The numbers speak for themselves - a Prius’ lifetime energy consumption is far less than that of a Hummer H2, or even the smaller H3. Toyota’s argument seems solid - a the running of a vehicle uses far more energy than its manufacturing. About 74% of a Prius’ lifetime energy is spent burning fuel, while the H2 and H3 use around 87% and 88% respectively.
Please feel free to crunch some numbers and point out if I’ve made any calculating errors.
Sources: Ask Pablo, vcacarfueldata.org.uk, Car and Driver
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Comments
Thanks for the comment, Paul. It’s my understanding that the GREET model factors recycling into its figures.
[…] earlier post comparing the Prius’ green credentials to a Hummer’s turned out to be something of a […]
I thought the Prius is dirtier because of the nasty intensive process the battery takes to be made. Not to mention, when it needs to be recycled.
Nothing to do with the weight of steel or any of that.
The weight of each component is vital to calculating how much energy is required to manufacture a vehicle. Obviously, 2kg of steel bodywork requires more energy to make than 1kg of steel bodywork.
The GREET model takes into account how much energy is required in the manufacture of each component of a vehicle, including the NiMH batteries in the Prius, that’s why the model states that a hybrid requires 85209BTU of energy per kilogram of vehicle to manufacture as opposed to the 69142 BTU needed to make a kilogram of a conventional internal combustion car.
The GREET model also takes vehicle recycling into account.
The fact remains that the actual driving of a vehicle comprises a far bigger portion of its overall lifetime energy usage than its manufacturing does, so even though a hybrid is more energy intensive (per kilogram) to make, it more than offsets this difference in the amount of energy it saves while driving.
“The GREET model also takes vehicle recycling into account.” Good.
But, I don’t know if the Prius’ entire battery system can be recycled. Can it? If not, then what happens to the batteries? And is that still terrible for the environment, even if it’s impact is lesser than an H2 or H3?
And the figures of gasoline usage/impact are dubious. Virtually no Prius owner gets anywhere close to 50-60 mpg. They get more like 40-45 mpg. [Noted exception: the handful of extreme mileage owners that really go, wonderfully, nuts with stretching their mileage through driving habits, and modifications.]
Thanks for posting this entry, btw!
Re Edwood : “Virtually no Prius owner gets anywhere close to 50-60 mpg”. FYI, I just did a 5 day 4000 Km trip from Melbourne to Gold Coast & return in a Prius. Fuel consumption was 5.3 litres/100 km overall. This was at max legal speeds throughout, typically a steady 101 or 111 km/h through both flat & hilly country. That’s 53 mpg if you use “proper” Australian/English gallons or 44.3 mpg if you use US gallons, which are smaller.
(Be careful when comparing consumption figures : the biggest single influence on what mpg you get is obviously what country you live in ! )
Sorry Carl, but upon examination the GREET models do not take into account the Prius’s unique construction model.
While they might work for a 100% domestically produced hybrid, they do not account for the transport of the nickel from Canada all the way to Asia to be crafted into the the battery pack, and then shipped all the way back here for final assembly.
Actually, the batteries are currently built in a total of no less than three countries, and that doesn’t count the sources of all the parts, which will probably involve half the known world. The complete transportation cost involved is staggering. Toyota is opening a battery construction plant in (I believe) Fremont, CA, USA. This should help reduce the energy cost of construction for USDM vehicles.
Very interesting indeed, thank you Carl!
I have been waiting for you to comment on this for a while now…my only little bit of extra to the conundrum comes into the final recycling bit…i.e. when the poor old thing comes to rest in some scrapheap.
Is it not at that point that the Prius, sadly, will not give up…and will carry on polluting the atmosphere for the next 100 years?
The Hummer and my Isuzu 3.0 litre 4×4 diesel will happily allow themselves to be given up and reborn into something else ;0), whereas the Prius, simply digs its heels in in certain areas, and cannot be recycled?
Cheers, and thanks for the info.
Paul