Reducing the Electric Vehicle Carbon Footprint

March 7, 2023 § 2 Comments

Electric vehicles are critical in the effort to mitigate climate change effects. But they do have a significant carbon footprint, driven by the fact that more energy is used to manufacture an EV than an equivalent gasoline driven car. Over a lifetime of use, however, the emissions from gasoline combustion dominate. A study at Argonne National Laboratory estimates that the lifetime greenhouse gas emissions from EVs are 40% of those from gasoline powered vehicles, as depicted in the figure. We discuss here how we could do better than that.

Source: Argonne National Labs GREET 2021, as cited in Electric Vehicle Myths | US EPA

The variability in the particulars of both types of vehicles necessarily makes such estimates inexact, and yet instructive. Both have assumed lifetimes of 173,151 miles and the EV has a range of 300 miles, while the gasoline engine delivers 30.7 miles to the gallon. This places the vehicles roughly in the vicinity of compact cars or small SUVs. With the decimal points and all, you know a model dictated the results!

In the bottom two buckets, the bulk of emissions are from energy used in the manufacture of materials and assemblies. For most metals, primary production (from ore and other sources such as brine) is more energy intensive than secondary production, also known as recycling. In steel, for example, a tonne of conventional steel has an associated CO2 production of 1.8 tonnes. An improved process, known as Direct Reduction Iron (DRI), with limited scalability, has a third of that, and with a variant that takes it to near zero. Scrap iron and steel, simply melted with some refining action, has a fraction of the DRI figure. But due to economic availability, only 30% of steel is from scrap.

EVs have on average 900 kg steel, which is about 6.9 grams/mile, or about 27% of the “other manufacturing” component in the figure. Green steel use would eliminate most of the steel contribution. The steel industry is actively addressing the issue. One startup is producing electrolytic iron, which is green if the electricity is carbon-free. Carbon capture at the iron production source would get most of the job done economically in areas such as Europe with an explicit price on carbon.

Minerals other than iron comprise 210 kg per vehicle on average. The largest contributors are graphite 66.3 Kg, nickel 39.9 Kg, and cobalt 13.3 Kg. Significant energy is expended in their production, even though graphite is largely a derivative of a petroleum refining waste. When batteries are recycled, nickel, cobalt and lithium will have lowered carbon footprints.

The gray portion is the largest contributor in EVs, and mostly comprises the carbon emissions associated with the production of electricity. In this figure, they used the national average for the US in 2020, when the renewable portion was 21%. The Energy Information Administration forecasts that figure to double by 2050. To the extent that EVs are charged in homes, averages apply. But public charging could well use a higher proportion of carbon-free power. A startup in India has a portable solar unit for charging stations.

The gray component is also affected by electricity used per mile. These figures are notoriously hard to compute because vehicles and driving conditions vary. One of the earliest cars to go all-electric was the Nissan Leaf. It came out with a 40-kWh battery pack which targeted range of 149 miles. This computes to about 0.27 kWh per mile. Later models with a 62-kWh pack had a range of 226 miles. This too computes to 0.27 kWh per mile, which is a trifle surprising because the heavier pack ought to deliver worse mileage. I calculated battery pack weights for several models and found 6.4 kg/kWh to be a reasonable figure. The newer Leaf model could have been expected to be 141 kg heavier than the earlier model which weighed in at 1490 kg. But the effect of greater weight is felt in pickup trucks. From public records I conclude that the Ford F150 Lightning and the Rivian R1T clock in at 0.49 and 0.42 kWh per mile, respectively. This is not surprising because these vehicles are more rugged and built to pull loads.

Electricity will get greener over time and recycling will surely become more common, if for no other reason than worries about supply of lithium, cobalt and nickel, and concerns about dodgy working conditions in the countries home to the major supplies.

 I decided to use the Hyundai Ioniq 5, the Motor Trend SUV of the year, for a discussion of driving options. This model, as do many of the others in the same general category, offers two range options: 240 miles range with a 58-kWh battery, and 300 miles with 77 kWh. Based strictly on battery size, the weight difference is nearly 7%. I compute battery cost difference to be about USD 3800, based on an estimated battery retail cost of USD 200 per kWh. So, a consumer is paying more and emitting more CO2 (due to increased weight) by opting for the longer range. But what if Level 3 (high voltage DC) fast charging were available at multiple points, including every rest stop on the highways? I estimate that Level 3 chargers can fill at the rate of 3 kWh per minute. That means the difference in capacities of the two versions of the Ioniq 5 can be made up in 6 minutes. 6 minutes. That’s shorter than the time at the rest stop to hit the rest room, or “walk” the dog, or grab a snack. Curiously, the battery size difference for the Ford F 150 Lightning is also the same as for the Ioniq 5, although the CO2 penalty per mile is greater for that vehicle, as discussed in a recent NY Times piece. But the consumer can opt to buy the lower range model and make up the difference in range with only minimal inconvenience.

Existing plans to decarbonize the grid will drive down the carbon footprint of EVs, as will any policy drivers to encourage recycling of EV batteries. But interestingly, investment in Level 3 charging infrastructure could influence consumer behavior which results in reduction in use of critical minerals such as cobalt and nickel, with a further knock-on effect of reduction in carbon footprint. Critical minerals access could be important when EV adoption hits high gear and puts strains on the supply chains. And every carbon mitigation approach is another brick in the wall*.

Vikram Rao

*just another brick in the wall, from Another Brick in the Wall, by Pink Floyd (1979), written by Roger Waters. Not the common interpretation of the lyric.


§ 2 Responses to Reducing the Electric Vehicle Carbon Footprint

  • Abe Palaz says:

    Vik, Thanks for this article and your excellent comparisons. The way I look at the whole EV picture is that they have come a long way, but they still have a way to go for broader market penetration. A successful battery technology will win big and that is where the bottle neck. A successful battery has to satisfy multiple parameters; distance, ease of charge, CO2 fooprint, low cost etc.. I can not wait to see the winner.

    Regards Abe

  • Rogelio Sullivan says:

    Great article! I’ve often lamented the price premium that some EV buyers pay for the larger optional battery; because in everyday driving, it’s not really needed. Your analysis confirms this and estimates that they can avoid the cost, but obtain the additional range for long trips in just 6 minutes on a DC fast charger. I hope more EV buyers see this and keep their $$$ in their pockets.

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