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To describe fuel economy of EVs manufactures and Environmental Protection Agency (EPA) use the concept of MPG Gasoline Equivalent (MPGe). According to the concept, one gallon of gasoline is attributed with energy of 33,7 kWh. For example, 2020 Tesla 3 Standard Range is labeled with a combined fuel economy of 131 MPG. This means that EV’s battery needs to get from an external power source such as a grid or charging station 33,7 kWh of electric energy to enable a vehicles with 131 mi. driving range. In other words, vehicle’s fuel efficiency is [33,7/1,31], i.e. around 26 kWh/100 mi.
Does it mean that the cost of electricity for 2020 Tesla 3 Standard Range is [131/30], i.e. 4.4 times cheaper than the cost of gasoline for comparable in class and pick-up time vehicle, 2020 BMW 330i, with combined fuel economy of 30 MPG? The answer is: no, not even close.
To accurately compare the cost of electricity for an EV and the cost of gasoline for conventional IC engine vehicles, it is necessary to attribute EV with so called True Fuel Economy (TFE), and then directly compare it with the fuel economy of a conventional IC engine vehicle.
TFE of an EV is defined as the fuel economy of a comparable IC engine, i.e. the vehicle of similar class and having 0-60 mph pick-up time substantially the same as that of the EV:
(D/De)*CE=(D/TFE)*CG,
where D is the distance driven; CG – national average cost of one gallon of gasoline; CE – national average cost of one kWh of electricity; De – distance that an EV runs on one kWh of electricity (De=MPGe/33.7 kWh). According to the equation, TFE can be calculated as follows:
Since costs of electricity and gasoline may vary on the location, to obtain an accurate estimate, it is necessary to use annual average costs for a particular territory.
Here is an example. In 2019, TFE of 2020 Tesla 3 Standard Range was [131*0.59], i.e. around 77 MPG. Accordingly, the specific cost of electricity for 2020 Tesla 3 Standard Range was [77/30], i.e. 2.6 times lower than specific cost of gasoline for 2020 330i BMW, having a combined fuel economy of 30 MPG.
