In essence, the Model 3 powered off an electric grid which was 100% coal fired, it would still emit the same CO2/mi of an ICE vehicle that could achieve 50mpg. There’s no comparable to a pure ICE vehicle that can achieve 50mpg, or even close to it to it in its class.
The truth is that in the US the grid of utilities produces less CO2/kWh. The coal industry has been declining in value as a fuel quite rapidly dropping to 27% and , with the planned closures of plants, it will fall to 22 percent in 2022. Natural Gas has been replacing the majority of this with half the amount of CO2 produced per kWh. Renewables have replaced the remainder. However, as renewable prices drop increasing and more, they’re growing faster as Natural Gas so will be decreasing the price of Natural Gas as time passes.
Additionally, one could consider the area they reside in and the way it compares with other cars as to the mpg of a car that is equivalent to based on the charging of the grid.
Here’s a map of the how much mpg an EV is equivalent to that’s Model 3, Hyundai Ioniq and Prius Prime charging off from various parts in the grid (based on the 2016 generation of sources.) Be aware this: O’ahu was actually less than 50mpg because at the time, it was around 3/4 Petroleum and a little less than 1/4 Coal , and there was not much else. It was a little less efficient than pure coal but still comparable to 47mpg by CO2 for every mile driven.
UPDATE 02/14/2020: Time advances. The map above was based on the electricity production data for 2016. Let’s take a look with the 2018 electricity production figures.
We just keep going more eco-friendly.