How do we know if a product is “green” or “sustainable”? Consider the Life Cycle Analysis of cars performed by CNW in 2007 (here (PDF)). One of the more controversial conclusions of the study was that the Prius is less sustainable than a Hummer (H2 and H3).
Naturally this created an uproar in the community. The Hummer is clearly a more energy intensive vehicle than the Prius. So why did CNW conclude otherwise?
The answer lies in the details of performing a life cycle analysis. They were not looking at fuel economy as a sole metric of the life cycle of the vehicle. They considered the amount of energy spent in designing, manufacturing, transporting components, repairing, and driving the vehicles.
A great deal of attention was given to the nickel used for the Prius batteries, which travels around the world before it gets in the battery of a new car, which is one of the parameters involved, but there are many more. For example, the Hummer was built off an existing platform, so the energy required to design and develop the H2 was much less than the Prius, which was a brand new design and could not take advantage of much of the existing production technology.
Not surprising – the first truly mass-produced hybrid vehicle is going to take a great deal of effort and design. Certainly more than the succeeding generations and other brands.
It seems to me that the biggest parameter associated with the conclusion was the projected life span of the vehicle. They were calculating the total energy per mile for the life of the vehicle. This means you figure out the total energy required to design and manufacture the vehicle plus the energy associated with repair components, and divide that by the number of miles the vehicle is expected to function. Then you add to that the fuel efficiency associated with driving.
It is obvious that the fuel consumption for the Prius is going to be significantly less than for the H2. So the longer you drive the cars, the better the Prius looks. What made the Hummer come out better was the expected number of miles for the useful life of the car.
In 2005, the year for which the data was collected, Prius owners were driving very short distances per year according to the self-reported data collected by CNW. Much less than H2 drivers. This data, combined with the warranty information from the manufacturers, led to the mathematical conclusion that a Prius will have around 100,000 miles of useful life and the H2 around 300,000 miles.
So, the fixed energy of the H2 is spread out over 300,000 miles, but that of the Prius by only 100,000. In other words, the energy of the Prius was expended 3 times as fast as the energy in the H2. It should be no surprise that the Prius didn’t look good!
In successive years, the Prius drivers started reporting more miles per year, and the energy intensity per mile dropped, and is now considered more energy efficient than the H2.
It is important to understand the total energy impact of anything we produce or purchase. But trying to reduce a product to a single value inevitably leads to misunderstanding and confusion. Products need to be evaluated by a multi-faceted expression of their sustainability impact. To paraphrase mathematics, sustainability ratings do not form a well-ordered set. I will be exploring what this means in future posts.
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I find life cycle analysis process to be highly frustrating – not because they are not accurate and not because they are based on numerous value based assumptions. My frustration lies in how people use life cycle analysis as a basis to make arguments for changes in policy, behavior or product description. The hummer/prius debate is interesting because the study goes into great detail on the development and manufacturing side of the equation but essentially ignores the details of the fossil fuel use of the vehicles. if we begin to take into the account the full impacts of gas guzzling vehicles including war, oil spills, and more, the life cycle equation will quickly tip in favor of the prius. how do we put a price on losing a life in defense of oil fields in the middle east? Its because of our country’s citizens addiction to oversized and wasteful vehicles that we find ourselves in wars overseas and because thousands have lost jobs in teh auto industry. So before we award the hummer a prize for sustainability, we should acknowledge the imperfection of the life cycle analysis process and then but an asterisk to any conclusions gleaned from such processes.
You are correct that Life Cycle Analysis does not take into account social phenomenon. Further, I think most people involved in LCA do fully acknowledge the imperfections of the process. Nonetheless, the LCA is still a very useful tool in understanding the energy consumption and investment in a product.
The argument that if we stopped demanding oil we could have peace in the world is a valid one, but does not weaken the value of LCA. One of the ways to reduce the oil demand is to understand the energy investment and consumption in products and attempt to minimize this quantity. This would reduce oil consumption in various ways.
Don’t forget that transportation is only about 28% of the US energy consumption. Cars consume about 32% of the transportation fuel. So if we were able to cut automobile consumption in half for every car in the country, we would only reduce our oil demands by 16%.
The problem is much bigger than how much gasoline is consumed per mile.
Don’t get me wrong – every little bit helps! But we need to think big – we need to address the manufacturing science, the sourcing issues, materials movement, etc.
The debate should be not between the life-cycle assessment of the Hummer and the Prius but rather between the costs and benefits of driving and other modes of transportation. LCA analysis to determine the lesser of two evils is not ultimately where we need to be spending our time, energy and efforts.
LCA has its place as a reminder to consider all aspects of a decision or choice. It is imperfect and inprecise but probably the best tool available for these sorts of things. But it doesn’t help us make the really big moves. That requires passion and emotion and humanity – not calculation and analysis
I agree that the social aspects of each should be accounted for. That being said, what are the social implications of purchasing a vehicle built in a foreign location vs. one built locally? What are the wages of the workers at each facility? What about suppliers for each product? (Since Hummer is no longer owned by GM, it cancels any argument for locally owned products.)
One large social aspect never accounted for in any of these arguments is the basic enjoyment of driving vehicles. Is that not a social benefit? I enjoy driving my large gas guzzling vehicle for the sheer fun of doing so. Do I need to have a large gas guzzling vehicle? No, but it is surely a fun way to go wherever I want to.
On a different note, what would the LCA of a full electric vehicle be? What about a PHEV? An electric vehicle by nature consumes much less petroleum, and has less environmentally harmful chemicals in general. No gas, no engine lubricants, potentially minimal transmission fluid or differential lubricants (depending on design), much less coolant. Then again, there’s a lot more copper or other metals used, not to mention the larger batteries requiring more metals (mostly Lithium).
So, the Hummer becomes more efficient the more it is driven! That absurdity is only possible because the LCA is considered in a social vacuum. In fact, neither the Hummer nor the Prius is in any sense of the word sustainable…..both rest on the top of the pyramid of high tech society which was enabled, and survives, only based on cheap fossil fuel, and 50-100 years from now, as I see it, they will be equally garish monuments to our lack of vision, and equally useless. In the absence of the fossil fuel subsidy, will we be able to sustain any mode of transport, even my beloved bicycle, other than our feet, our horses, and our sailboats? Although I’m not sure about cars, I’m confident the bike will be viable as long as I am shuffling across this mortal coil.
Just to clarify, the Hummer doesn’t become more efficient the more you drive it. The Hummer is more efficient because is lasts longer than the Prius (based on the data available at the time of the study).
This should not be a surprising outcome – the more disposable something is, the less environmentally efficient it is. If a car only gets 100K miles before it is trashed, it won’t have a good LCA.
That’s one of the payoffs with LCA – it makes us look at the entire life of the product. Sometimes the results are surprising, but we can examine the calculations and do some “mathematical tea leaf reading” to determine why the surprising result appears.
In response to Rob Diemer:
What do you think can be done if a person doesn’t have the passion, emotion and has a practical but very real obstacle to acting on a humane impulse? Is there a way to motivate such people? Should we try?