Vehicle Operation CO₂ Emissions: Gasoline versus CAISO Grid Power

Introduction

Fig. 1: Fuel Efficiency reading from 2019 Chevrolet Bolt. (Image Source: S. Kostelnik)

This report compares the CO₂ emissions released in order to drive one kilometer in an electric-powered vehicle (EV) versus a gasoline-powered vehicle (ICE). I find a 2019 Chevrolet Bolt EV to release less CO₂ emissions per kilometer driven than a 2008 Honda Fit ICE. Note that this only accounts for the emissions released to power the vehicles (Vehicle Operation emissions). It does not address other lifecycle emissions such as those released in vehicle production or in the precombustion fuel cycle.

Approach

The emissions of the two vehicles are compared in kg of CO₂ per kilometer traveled. This unit can be found by multiplying vehicle fuel efficiency (kWh per km for the EV and liter gasoline per km for the ICE) by carbon intensity of the fuel (kgCO₂ emissions per kWh produced in the grid or per liter of gasoline combusted in the vehicle engine). We have

Vehicle Fuel Efficiency

The individual vehicles I compare both indicate their average fuel efficiency on the dashboard display (see Fig. 1). The indicated values are

Carbon Intensity

The carbon intensity of electricity (kgCO₂/kWh_Grid) measures the amount of CO₂ emissions released by generation sources for the average kWh consumed by end users in the CAISO grid. According to the California Air Resources Board, the GHG emissions released to provide electricity to customers within the CAISO market in 2022 equaled 60 million metric tons of CO₂. [1] In that same year, CAISO reported the total electricity consumed by end users (load) within its area to be 210,879 GWh. [2] Dividing total emissions by total load gives

In other words, for each kWh the EV consumes in order to drive, an average of 0.28 kg of CO₂ is released by the various generation sources contributing to the CAISO grid. (See Note on Key Assumption below.)

The carbon intensity of gasoline (kgCO₂/L_gas) measures the amount of CO₂ emissions released from the Honda Fit for each liter of gasoline combusted in its engine. Gasoline has a standard carbon intensity of

per Environmental Protection Agency (EPA) standards. [3]

Vehicle Operations CO₂ Emissions per Kilometer Driven

With all variables defined, the vehicles can be compared in terms of CO₂ emissions per kilometer driven.

The CO₂ emissions for the EV are 75% lower than the ICE per kilometer driven.

Note on Key Assumption

A key assumption in this analysis is that the EV is charged with the average kWh in the CAISO grid from the 2022 year, so the carbon intensity factor is an average across all hours of the day throughout the 2022 year. If one were to charge an EV only in the daytime, the carbon intensity of CAISO electricity would be lower, given the proliferation of solar in California. If one only charged at night, when natural gas provides a large portion of CAISO electricity, the carbon intensity factor would be higher.

© Satchel Kostelnik. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] California Greenhouse Gas Emissions from 2000 to 2022: Trends of Emissions and Other Indicators," California Air Resources Board, September 2024.

[2] 2023 Annual Report on Market Issues and Performance," California Independent System Operator, July 2024.

[3] "Revised 2023 and Later Model Year Light-Duty Vehicle Greenhouse Gas Emissions Standards," Federal Register, 86 FR 74434, (30 Dec 21).