Damned lies and statistics on the embedded energy in hybrid and regular cars

What’s the energy cost embedded in every hybrid or gasoline powered car? That is, how much energy it takes to manufacture a car is the beginning greenhouse gas footprint of that car. Every manufactured thing involves extracting raw materials, processing them into parts, assembling into the final product, etc, and every step of the manufacturing process has side effects in energy consumption, materials consumption, and a slew of different environmental effects including greenhouse gas emissions, or toxic chemical releases, or land being used for factories instead of farms, and on and on.

With that in mind ponder this quote I found in a supposed news article that isn’t (it was more of a half baked incoherent rant):

“Making a Prius consumes 113 million BTUs, according to sustainability engineer Pablo Päster. A single gallon of gas contains about 113,000 BTUs, so Toyota’s green wonder guzzles the equivalent of 1,000 gallons before it clocks its first mile. A used car, on the other hand, starts with a significant advantage: The first owner has already paid off its carbon debt. Buy a decade-old Toyota Tercel, which gets a respectable 35 mpg, and the Prius will have to drive 100,000 miles to catch up.”

This conflates a couple ideas together to make it seem that hybrid cars must be horrible for the environment. Let’s try and separate them apart.

First, we have the concept of the BTU’s used to construct a Prius. BTU is the acronym for a unit of heat energy (“British Thermal Unit”) and is a convenient way of measuring energy, and comparing dissimilar sorts of energy. Hence the study by Pablo Päster the quote references almost certainly listed all forms of energy consumption in manufacturing a Prius, converting everything into BTU’s, and producing the final number. Likewise the “a gallon of gasoline contains about 113,000 BTU’s” comes from a chart published by the EPA known as the Gallons Gasoline Equivalent.

It’s interesting that a Prius requires 113 million BTU’s to manufacture. It’s convenient that this number is exactly 1000x the BTU’s in a gallon of gasoline. Hopefully the 1000x factor between the two numbers is just a random coincidence.

Ask yourself, though, why does the second half of this quote refer to a used car? Why does it not compare the embedded energy cost of the Prius against the embedded energy cost of some other equivalent size gasoline powered sedan?

By comparing the embedded energy cost of a new Prius against any kind of used vehicle, it’s automatically placing the Prius at a disadvantage. Yes, it’s true that the purchase of a Prius comes with an embedded energy cost, and hence an environmental footprint. But this is true for any sort of newly manufactured car. Why aren’t “normal” gasoline cars being subjected to this same scrutiny in the quote above? Why are only hybrid cars being scrutinized? And then why is the environmental footprint of a hybrid car compared to the environmental footprint of a used “normal” car?

An even more interesting question is why the used gasoline car is assumed to have no residual environmental footprint? That Toyota Tercel also required an energy input to manufacture. For that matter, so does any other gasoline powered car, or any other manufactured object. It’s not like this disappears after the first owner of the car. Instead the proper way to account for the embedded energy cost of any manufactured object, is to amortize that cost over the whole actual lifetime of the object. Hence, a five year old car will have had some of its embedded energy amortized away. A car that is driven for 2 years and then junked into the incinerator would have its embedded energy amortized over 2 years, whereas the identical car that lasts for 20 years will have its embedded energy cost amortized over those 20 years.

It’s wonderful that the quote above asks us to ponder the embedded energy cost of a Toyota Prius, but shouldn’t we also be asked to ponder the embedded energy of other sorts of vehicles?

Finally, the quote above touches into an interesting background idea. Namely, the opportunity for a hybrid or electric car to decrease the collective environmental impact of driving our butts around town. That is, if we compare the environmental impact of an electric (or hybrid) car versus an equivalent gasoline car, theoretically the electric/hybrid car will have a smaller impact per mile driven than the gasoline car. That’s why these things are desired, yes?

The quote above implies that driving a hybrid somehow pays for its embedded energy cost. How would that be? Both the hybrid and gasoline powered car has an embedded energy cost. What’s different is that the hybrid/electric car has a lower impact per mile driven than the gasoline car. Hence the lower impact per mile driven of a hybrid or electric car pays for its embedded energy cost.

Theoretically.

Again, to harp on the construction of that quote, by situating a new Toyota Prius against a used Toyota Tercel, the reader is led to create an incorrect perception of the relative energy cost.

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About David Herron

David Herron is a writer and software engineer living in Silicon Valley. He primarily writes about electric vehicles, clean energy systems, climate change, peak oil and related issues. When not writing he indulges in software projects and is sometimes employed as a software engineer. David has written for sites like PlugInCars and TorqueNews, and worked for companies like Sun Microsystems and Yahoo.