To calculate your home charging costs, you’ll need a few pieces of information.
1) Your electricity rate per kilowatt-hour
2) The size of the battery you’re charging
Let’s say you live in Louisiana, which happens to have the cheapest electricity rates in the United States. At time of writing, Louisiana’s average rate is 9.37 cents per kilowatt-hour.
Your car’s battery capacity is also measured in kilowatt-hours. Let’s say you drive a Tesla Model 3 with a 75 kWh battery pack.
9.37 cents x 75 = $7.02 for a full charge.
If you happen to live in Hawaii, you’re going to have America’s highest electricity rates. Hawaii’s average at time of writing is 32.76 cents per kilowatt hour. Let’s try that math again:
32.76 cents x 75 = $24.57. Yowza! Big difference, but still likely cheaper than a local tank of Aloha-state gasoline.
Now we must consider that electricity is not always the same price, even in the same place. Depending on your rate plan with your local utility, you may pay more at certain times of day, or more depending on how much electricity you’ve used during your current billing cycle. Many plans offer cheaper off-peak electricity rates overnight, which is exactly when you’d want to charge your car. When considering buying electric, you may also want to reconsider which plan you’re using for electricity. Some providers may offer rate discounts specifically for charging an electric car, but taking advantage of these rates may require installing an additional meter (which could cost as much as $1,000).
The cost of charging on the go can be very hard to predict. Some networks vary prices depending on the local electricity rates. Others leave rates and policy (time limits, etc.) up to the owner of the property where the EVSE is installed, leading to a wide range of different pricing models. Some will charge based on time spent at the plug rather than how much electricity you use (meaning the slower your car is capable of charging, the more you end up paying - another reason why a car's Maximum Charge Rate is important). In addition to electricity or time, some charging stations may charge a session activation fee. Others may increase in price after a certain window of time, or have “idle fees” for sitting on the plug too long after charging is complete.
In most cases, charging on the go will still be competitive if not outright cheaper than filling an equivalent tank with gasoline. There are some very useful apps out there that can help you find a nearby charging station and also quickly estimate its rate. We cover these in the ownership lesson.