How many miles do you need to drive your electric vehicle to offset CO2 emissions?
Electric Vehicles (EV) are often hailed as one of the solutions to reduce pollutants. However, most of the emissions from an Internal Combustion Engine (ICE) vehicle come from their operation, whereas a larger share of the EV emissions come from its production compared to the former. The reduction of emissions of an EV, therefore, depends largely on the fuel mix of the electricity they are charged on. Using the United States as an example, how much do you need to drive per State to offset emissions?
If we take a gasoline-powered ICE, there are a myriad of different sources of pollution coming off the exhaust: from carbon dioxide, to particulate matter, carbon monoxide, benzene, nitrous and Sulphur oxides, and more. On the other hand, the electricity grid relies on a variety of fuels and energy sources that differ by states, and while you can find most of the previous pollutants, it is in general easier to control pollution over large centralized power plants, in addition to the mix having several non-emitting sources like nuclear, hydro, solar or wind. Nonetheless, for ease of comparison, we will focus on offsetting carbon dioxide emissions (CO2).
The U.S. Environmental Protection Agency (EPA) considers that on average, the typical gasoline-powered passenger cars emits 251 g CO2 per km driven. Using Temporelli et al. (2020) comparison of an 40 kWh EV (commercial example, Nissan Leaf) to a similar petrol car, we can estimate the CO2 eq. emissions from production and maintenance of both types of vehicles, and compare it using US grid emission rates by state and the average emission rates for gasoline. This study considers 49.3 g CO2 eq./km for gasoline cars excluding fuel usage, and as much as 104.2 g CO2 eq./km for the EV with a life of 210,000 km for both. This means that ICE have embodied emissions of 10,353 kg CO2eq. and EV 21,882 kg CO2 eq. We will add 59.1 g CO2 eq./km to account for gasoline production as per the study mentioned, ending with 310 g CO2/km for the ICE. The EV requires 16.8 kWh per 100 km.
Using the average US 2019 grid, you need to drive an electric vehicle ~48,000 km or 30,000 miles to breakeven the emissions in comparison to a similar petrol car. The lowest figure is 37,250 km or 23,300 miles from Vermont, and the highest 75,000 km or 46,900 miles in Wyoming. Here’s how the map looks by State for the continental USA (for Alaska, the figure is 53,900 km and for Hawaii 62,800):
Nevertheless, the US grid has decreased its carbon intensity over time. And with many local governments and several corporations having ambitions for a net zero grid, we can expect that the trend will continue its path. Taking the average US grid CO2 intensity, we can run a very simple forecast into what the grid will look like in 30 years. The shadows represent the 80% confidence interval for the darker blue, and 95% for the light. The blue line is the central estimate. Based on this model using empirical data, the central forecasts for the mean CO2 intenstiy of the US grid for 2030, 2040 and 2050 would be 250, 160 and 110 g CO2/kWh respectively. On the plot below, you can see how many kilometers would be needed to offset each year. It is until 2050 that the grid would allow the mileage required to be below 40,000 kms as in Vermont.
But these do not reflect the situation in each State. If we run a similar model for the projections over 50 years for each Sate, and assuming no further efficiency gains from any type of vehicle, we can see which is the year (if ever) in which you offset the emissions driving the least mileage possible using Vermont as the benchmark. In Vermont, 99% of their electricity is sourced from renewable sources, which makes their grid have a CO2 intensity of less than 3 g CO2/kWh. We can then use this as an example of a very low carbon grid, with the 37,000 kms from VT as the lowest possible mileage with current EV technology. Since it’s hard for grids to reach this level of emissions, we will see when each state will arrive to 40,000 kms or 25,000 miles. driven For context, this amount is 1.85 times the average yearly mileage per American. We are ignoring the fact that as the grid gets cleaner the cumulative kilometers needed are less than show in the previous plots. In the map, the states that are not colored do not reach the benchmark in the 50 year period modelled.
Finally, Del Pero et al. (2018) is an excellent study on the environmental impact of small-sized vehicles in the European context with a mass of 1357 kg and a peak power of 93 kW for the ICE, and a mass of 1595 kg and peak power of 85 kW for the EV. While smaller cars are more efficient and European emission standards are tighter than those of the US, it is a very insightful glimpse into the different environmental tradeoffs for both types of cars. Using the 2015 European grid mix (~300 g CO2/kWh vs ~400 g CO2/kWh for 2019 in the US) and a mileage of 150,000 km, EVs outperform ICE on only one out of six environmental metrics: global warming. On the other five, acidification, human toxicity, particulate matter, photochemical ozone formation, and resource depletion, EVs outperform ICE on acidification if they are driven for more than 175,000 km under a Norwegian electricity mix (~16 g CO2/kWh) and 125,000 km for ozone formation only with the Norwegian grid, which relies on hydropower for 95% of its net generation.
If you truly want to protect our natural resources and minimize our impact on our planet, drive less and extend the lifetime of your vehicle as much as you can.
