50. Prius vs Pick-up, Can We Lay It to Rest?

 Prius vs Pick-up, Can We Lay It to Rest?


Despite our attempts to stay abreast of misinformation about current energy topics related to the climate crisis, we are continually caught off-guard by new doozies. One of those experiences was at the Common Ground Fair this year.


While staffing a climate solutions booth at the fair, one of us engaged in conversation with a friendly visitor who shared how much he regretted that electric cars were certainly no answer to the CO2 problem. “Well,” we ventured, “certainly not THE answer, but part of it?”


Oh no, he assured us, his son had learned at community college - they had “done the calculations” - that his diesel pick-up will have produced less CO2 over its 280,000 mile lifetime than a Prius would produce in its first year, if you count the CO2 involved in its manufacture.


Since the One of Us staffing that booth was not the one with the scientific cred, or even the information at hand, we could only ask for clarification. “Well it’s the lithium - do you know how much CO2 is involved in mining the lithium?” he demanded (smiling)? I had to admit (smiling) that I didn’t! Another factor, he assured me, was that diesel fuel produces “way less” CO2 than gasoline. Yes, WAY less. This basically left me speechless.


So, to help you, potentially another innocent, quasi-informed but ill-equipped person in a similar future situation, because who knows how many people “took this class,” let’s walk through it!

Let’s start with the diesel fuel used to drive the pick-up 280,000 miles. A gallon of diesel actually puts out 10% more CO2 than gas (it’s denser), but it can be argued that diesel vehicles produce less CO2 because diesel engines are 20% to 30% more efficient than gasoline engines, and will thus put out 14% to 20% less CO2 per mile, given two vehicles of the same weight. But that benefit is partially offset by increased output of nitrogen oxides, which are also greenhouse gasses.

We don’t know exactly which truck he was using, but he referred to a 1999 “power stroke” diesel which is used in a Ford F-350. Its typical fuel rating is around 13 MPG. Over 280,000 miles it would burn more than 21,000 gallons of fuel. A gallon of diesel produces around 10 kg (22 lbs) of CO2, so the truck would put out 210 metric tons of CO2 over 280,000 miles.

A standard (non plug-in) Toyota Prius hybrid is not an electric car, it is a gasoline-powered car. All the energy to make it move comes from gasoline, and it averages 50-60 mpg due to the interaction of the engine with an electric motor and a storage battery. The batteries in the Prius are storage devices. They take some of their energy from the gasoline engine at times when it is not working as hard to push the car, and some from “regenerative braking” where the electric motor runs as a generator when the car is slowing down or going downhill.

This stored energy is used by the electric motor to give extra power when called upon for acceleration and going up hills. This balance between electric and gasoline power allows the gasoline motor to run more efficiently, resulting in a fuel economy that far surpasses other vehicles of the same weight and power. Over 280,000 miles the Prius would emit around 46 tons of CO2, compared to the above truck’s 210 tons just from burning fuel.

The standard Prius has a 1.3 kW battery. A 2019 comprehensive life cycle analysis from the IVL Swedish Environmental Research Institute determined that production of a 1 kWh battery requires around 300 kWh of energy and produces the equivalent of between 60 to 100 kg (130 and 220 lbs) of CO2. (This analysis includes all the steps in making the battery, including mining and transporting the necessary resources.) Mining accounts for around one-third of the emissions. 

So the Prius battery is responsible for less than 0.13 tons (130 kg) of CO2. That much CO2 is put out by burning about 13 gallons of diesel fuel. 

This analysis assumes standard energy sources, which are fast shifting to more renewables, and does not consider recycling of battery components, which will increase with the availability of used batteries. 

So what about the energy inputs and CO2 output from the manufacture of the entire vehicle? We find these numbers a bit harder to nail down. Based on values we have found for comparable vehicles we estimate around 15 tons for the Prius and 25 tons for the pick-up. The grand total is then 61 tons of CO2 for the Prius and 235 tons for the pick-up. You can see that the battery is a relatively small contributor to this total. We also see that fuel consumption is the main source of CO2 over the 280,000 miles.

So now you, kind reader, are better equipped than one of us was when you next encounter such an assertion by friend or foe. It seems even the friendliest of fellow citizen-consumers can be indoctrinated by apparent authority such as a school instructor. Note also that such wisdom, so gleaned, can be persistent: The encounter reminded us of a “study” that came out in 2006 that a 17 MPG Hummer was better for the environment than a 50 MPG Prius. The study was completely flawed and debunked, but it still circulates on the internet. 

Paul Stancioff, PhD., is professor emeritus of physics at UMF. Cynthia Stancioff re-words everything he writes. Email: pauls@maine.edu or cynthia.hoeh@gmail.com


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