First week without tailpipe CO2 -- Update

The article below first appeared as a shorter post on 17 June 2022. This 25 June update includes CO2 emissions related to materials and manufacturing or M&M CO2e (e means equivalent, as other greenhouse gasses are involved). You will see it is a smaller effect than either gasoline tailpipe CO2 for an internal combustion vehicle or source electricity CO2 for an electric vehicle.

For the last academic year, I had a weekly Energy & Society meeting with three wicked smart honors students where we talked about the energy transition, fuel sources and greenhouse gases. Somewhere in there I started to feel like a phony since my daily driver was a 13 mpg gas guzzling, CO2 spewing monster. After spring semester, I sold the guzzler and last week bought a 2017 plug-in hybrid electric vehicle (PHEV) quickly named Sparky (not very original, I know). Sparky has about 50 miles range in electric vehicle (EV) mode and gets 42 mpg when the battery is depleted and the gas engine has to kick in to turn a generator to power the electric motor. Sparky plugs into standard 110V every night and by morning is fully charged. My return distance to work is 6 miles and even with several errands over the last week the gas engine has never had to kick on. Zero tailpipe emissions for the first week of driving in my adult life.

However, we also need to consider the electric power source and it's CO2 output. In my part of Arkansas, the electricity comes from a coal-fired power plant way up in the NW corner of the state. The utility company estimates 1.02 kg of CO2 is produced for every kilowatt hour (kWh) of delivered electricity. For comparison, gasoline burning in an internal combustion engine (ICE) produces 9.07 kg_CO2/gal. Currently we can say gasoline is $5/gal and my home electric bill tells me I pay $0.08/kWh.

The last piece of the CO2 story for Sparky and the guzzler is to estimate M&M CO2e for each vehicle. A daunting challenge, but luckily we have the 2021 Polestar EV lifecycle sustainability report (google it, Polestar is the EV spinoff from Volvo). Disclaimer: Sparky is not a Polestar vehicle, we are just using Polestar data to estimate M&M CO2e. Figure 1 of the 2001 report is the key. Assuming things scale linearly and a 150K mile vehicle life, we can derive the following estimates. For the guzzler M&M works out to 17 tCO2e or 0.113 kg_CO2/mi when broadcast over the vehicle life. M&M CO2e for Sparky is 20 tCO2e (of which 1.7 tCO2e is the 18.4 kWh battery), or 0.133 kg_CO2/mi, somewhat higher than the guzzler.

The experiment: On 17 June, Sparky and I did an experiment in EV mode to find we used 9.1 kWh to drive 34.5 miles, or 0.264 kWh/mi. We have two stories for today's experiment:

The CO2 story: As said earlier, Sparky had no tailpipe emissions today, but electricity source plus M&M CO2 is (9.1 kWh)*(1.02 kg_CO2/kWh) + (34.5 mi)*(0.133 kg_CO2/mi) = 13.9 kg_C02. For the guzzler, this 34.5 mi trip would have required 2.654 gal of gasoline and produced (2.645 gal)*(9.07 kg_CO2/gal) + (34.5 mi)*(0.113 kg_CO2/mi) = 27.9 kg_CO2. In other words, Sparky's CO2 footprint in EV mode is 50% less than the guzzler.

The $ story: The cost for Sparky on today's drive is (9.1 kWh)*($0.08/kWh) = $0.73, while the same drive in the guzzler would cost (2.654 gal)*($5/gal) = $13.27. To bring this difference into focus, consider someone with a 34.5 roundtrip commute each workday for a month. Driving the guzzler would cost $265 in gasoline; while Sparky would add a bit less that $15 to your home electric bill.

Of course, we could quantify that money difference to some massive percentage, but what is the point? We can all afford $0.73 or $13.27 and that is part of the problem. Looking only at the money diminishes the more important CO2 story. But that said, it feels amazing to cruise around town all day on less than a dollar. In a way it feels like the past (1940 was the last time you could by 2.654 gallons of gasoline for seven-two cents), but it feels far more like the future.