HybridCenter Q&A: To Trade or Not to Trade?

Interesting question that I thought might be more widely informative:

Q: A friend of mine drives a 25-year-old gas guzzler.  His mileage is terrible, but he thinks he's probably doing the ecologically right thing by holding on to his old car, given the resources and energy required to make a new car.  I had never considered this angle, which seems crucial to acting in an environmentally responsible way.

I wonder if either of you have ideas about this or know of a resource to consult to help one assess the full impact of one's consumption.  Trading your old station wagon for a Prius, or recycling your old air conditioner and buying a newer, more efficient model, is it really saving energy? 

A: A variety of reputable investigators have concluded that 85-90 percent of energy use and global warming emissions attributable to an average vehicle over its entire lifecycle come from operation. Only 10-15 percent is production and disposal. This is true for both hybrids and conventional vehicles.

In order to achieve a net reduction in per-mile global warming emissions, (i.e. to offset the additional emissions from manufacturing and disposing of another vehicle) the new vehicle will have to get 10-20 percent better fuel economy than the old vehicle, assuming the vehicle will be driven in a typical way (i.e. that it will be used for its full useful life - usually around 170,000 miles).

Or, to look at it a different way, how long would it take to offset the manufacturing and disposal energy associated with the new car?

Assuming 15 percent of lifetime energy use for the new car is manufacturing and disposal, and a lifetime of 170,000 miles, you can calculate the miles which you need to drive in order to make up for the manufacturing and disposal of the new car, using the following formula:

Miles = 25,500 / (MPG_new / MPG_old - 1)

For example, suppose his old vehicle gets 15 mpg and he's considering replacing it with one that gets 35 mpg. As soon as he's driven  25,500 / (35 / 15 - 1) = 19,100 miles, he will have already made up for the energy and global warming emissions that went into producing that vehicle. For the remaining 150,000 miles of the new vehicle's life, the reductions in global warming pollution are all "profit."

That's not to say he should drive his old car another 19,000 miles. Not at all. So long as he replaces the old car with one that gets at least 10-20 percent better fuel economy, he should make the replacement right away.  In certain situations, it may take longer for fuel savings to make up for the manufacturing emissions. For example, if the driver does very little driving, it will take longer to offset the manufacturing emissions, and it may be worth discounting future emissions - something that's beyond the scope of the current discussion.

Posted by: Don

Comments

[David Pool]

Has anyone -- manufacturer, scientific organization, anyone -- yet responded to the report that was issued earlier this year by CNW Market Research (which is really industry guru Art Spinella)? This two-year study concluded that, when considering the energy necessary to plan, build, sell, drive and dispose of a car from the initial conception to scrappage, hybrids cost more in terms of overall energy consumed than comparable non-hybrid vehicles. But even more surprising, it concluded that smaller hybrids' energy costs are greater than many large, non-hybrid SUVs.

I had assumed that once CNW released details on their methodology that there would be much critical analysis of the report...yet I have seen or heard nothing.

[Tim]

The CNW study was full of strange math and laughable assumptions. For example, it summarilly claims hybrid (Prius) will last only 100K miles while a truck will last 250K miles. It also included R&D cost and several other factors.

Strangely, Canadian Taxi companies using Prius as Taxi's reports 410K km. See link below.

http://www.hybridexperience.ca/Toyota_Prius.htm

I am not sure this CNW thing is worth the paper it is printed on. A real unbiased study would try to isolate all factors used specifically for hybrid and all comparable factors used specifically for conventional cars. It does not seem like that is what they did. This may be why no one paid it any attention.

[Matthew]

Does the "miles" formula care what the purchase price of the new vehicle is? It seems like a more expensive vehicle would take more energy to produce (higher manufacturing cost, more labor/trips to the office for engineering, etc.)

I can see how the formula can get very complicated like investment analysis.

[Harry Stone]

Great blog you have, i am doing a study on this subject and i fund some great information on your site

Thank you for that

Harry Stone