DIMO Insights #4 - How Much Does It REALLY Cost to Drive Your Electric Vehicle?

Introduction

Have you ever wondered exactly how much you’re spending to drive your electric vehicle? If you’re scratching your head trying to decipher your electricity bill or not sure how efficient your car is in terms of miles per gallon equivalent (MPGe), you're not alone. 

DIMO can help you calculate these costs! For example, if you drove 100 miles in a 25 mpg internal combustion vehicle, it would cost about $16, whereas an example EV would spend around $4.50 to go the same 100 miles.

The Problem

Most electric vehicle (EV) owners have faced this challenge: Your home electricity bill doesn’t really break down the cost of charging your car, so it’s tricky to determine the exact cost of your electric vehicle trips.

And for fleet owners, there’s an additional layer of complexity. They must weigh the benefits of off-peak charging against the initial expense of an intelligent charger.

The Solution Explained

By examining the state of charge at the end of one charging session and the start of the next, and multiplying this by the battery's capacity, DIMO can accurately determine how much energy was used. Also, by looking at the miles driven between these charging sessions, we can compute the MPGe (miles per gallon equivalent, a measure of energy efficiency). Lastly, by looking at the location and month that the charging takes place, we can estimate the cost of energy and therefore the cost of driving per mile.

Let's break it down with an example:

Say your vehicle has a battery capacity of 75 kiloWatt-hours. Here's a hypothetical driving event (and the charging sessions before and after):

After Charging Session 1, your battery is 80% full. You drive around and by the time you decide to charge again, the battery's state is down to 40%. This means you've used 40% of the battery capacity, which translates to 30 kWh. If you drove 100 miles with this energy, your MPGe would be 89 (using the standard 33.7 kWh as the energy content of a gallon of gasoline).

For the costs, assuming you're paying $0.15 for every kWh of electricity (the average cost in Illinois in June 2023), the charging sessions have the following costs:

Charging Session 1: 45 kWh * $0.15 = $6.75

Charging Session 2: 22.5 kWh * $0.15 = $3.375

And since the driving session used 30 kWh, the cost per mile is calculated as:

Driving Session 1: 30 kWh * $0.15 per kWh / 100 miles = $4.50 / 100 miles (or $0.045 per mile)

To add some context, if an internal combustion engine vehicle averages 25 miles per gallon during a drive, and the cost of a gallon of gas is $4.00, then the cost per mile is $0.16. For example, if you drove 100 miles in a 25 mpg internal combustion vehicle, it would cost about $16, whereas this example EV would have spent $4.50 to go the same 100 miles.

Here is the average cost per kWh per US state for June 2023 (but, don’t worry, DIMO can automatically use the energy pricing for the state that your charging session occurs in):

Additional Insights for Drivers

If you have variable pricing for electricity based on the time of day or week (peak and off-peak rates), this method also helps you calculate how much a trip would cost, taking those fluctuations into account.

This information is invaluable for EV owners and, when applied on a larger scale, can also assist fleet owners in assessing the true cost of driving based on actual driving behaviors and energy pricing variations.

Visualizing Your Charges

To make it even more user-friendly, we're working on ways to visually present this data, so at a glance, you can get insights into your charging habits and costs. The diagram below visualizes the charging events and the energy lost during the charging session (due to things like heat loss):

Conclusion

Owning an electric vehicle doesn't mean you should be in the dark about your energy usage and costs. By understanding the real expenses associated with driving and charging, you can make more informed decisions, optimize your charging habits, and even save some money along the way!