EV Economics in the First Year

I have owned my Bolt EV for about 13 months now. The first few weeks I used the charger that came with the car (a level 1 charger). This charger is pretty dumb and I couldn't get much information about the charging process. However, at the end of March of last year I installed my level 2 charger which is a JuiceBox 32 and since then I have kept fairly good track of my usage. So this posting is about the year from April 1, 2021 to March 31, 2022.

The record is not perfect. The biggest issue is that when I go to Galveston I use the level 1 charger. There may be as many as 10 charges that are not accounted for (mostly from 50% to 100%). There were also some charges at my mother-in-law's house (probably 3) and at my parents house (one charge). So in the year there are about 14 charges of various sizes. My rough calculations say I am missing about 500 kWh over the course of the year. This could be as much as 5% and I am going to ignore it. So, keep that in mind when reading this.

I drive a lot more than most people. In the 12 months under discussion I drove 33,694 miles.

Lets start with a few charts:

This chart shows usage and cost. The left side shows kWh usage and the right shows cost. Blue is utility usage and red is DCFC usage. In September our electricity provider raised their rates which causes the difference in the blue cost to usage ratio.

Note that the big spike in May is real. I took a 1700 mile trip across country and charged mostly using DCFC. Then in June I had no fast charges at all. Starting in July my wife was living in Galveston and I was going to see her every two weeks.

I think this chart clearly shows the cost difference between home charging (blue) and DC charging (red). Most of my DC charging was at Electrify America; however, during the May trip I also used Charge Point and EvGo. I paid as much as 67 cents per kWh (and as little as zero). The average for May was 25 cents. By contrast the average for October was just 17 cents per kWh; there was two free charges and the rest were Electrify America.

Every month includes at least one free charge. Also it may be worth knowing that my utility cost is about 9.3 cents per kWh.

Here's another interesting chart:

So this shows the efficiency of the Bolt per month (blue) and the cost of electricity per mile (red). Note that in May efficiency stayed about the same but the cost per mile jumped way up. Again this shows the effect of using a lot of DCFC.

I find the slow climb of efficiency from April to October interesting. I think this is me learning how to drive the Bolt well and to use regen in a consistent manner. Finally after October you can see the effect of winter (Central Texas winters are weird; I think there was a cold snap in November and then it got really cold in February, but December and January were nice).

Now for the numbers: I burned through 10112 kWh of electricity. Getting an average of 3.7 miles per kWh. The total cost was $1189 or about 3.1 cents per mile.

My estimate is that if I had driven the same amount in my Miata (which gets about 28 miles per gallon on the interstate) it would have cost me $3900. So I saved about $2700 on the cost of fuel. There were no other maintenance costs on the Bolt. In the almost 34,000 miles the Miata would have needed about 7 oil changes for a cost of about $560. For a total savings of $3260.

I got a good deal on my Bolt and worked to keep the payments low; the savings in operating cost paid for over half of my car payments last year.

I am glad that my car does not pollute the air (at least not directly) and I am glad that the car is way fun to drive. But the economic case is hard to beat.

One final note: Battery degradation. I have run capacity tests three times. My confidence in the procedure is not that great. But I do see slight degradation of capacity. At 14000 miles I showed less than 1% (I would say not measurable with the technique). At 21000 I shows maybe 2% and the latest was at 37000 and was between 2% and 4%. I think this is about the expected pattern. I will continue to do tests from time to time and post the results when I have something I am confident in.