40K Mile Statistics

I recently hit the 40,000 mile (64,373 kilometer) mark.  At this milestone, I thought I would look at some interesting data about the car’s energy use and costs in comparison to a traditional internal combustion engine (ICE).  I also looked at how much my battery has degraded in the two plus years of ownership.

Energy Use vs ICE

Over those miles, the car averaged 326 Wh/mile and used 13,078 kWh of energy over exactly 40,132 miles.

How do I compare this to driving an ICE vehicle and using gasoline? This part is a bit tricky because the conversion of electricity to gasoline can be done a number of ways.  The more common (and conservative) number listed is 1 gallon of gas is equivalent to 33.6kWh.

13,078kWh * 1 gallon / 33.6kWh = 388 gallons of gas

40,132 miles / 338 gallons of gas = 103 MPG

The EPA number for the Model S is 89 MPG, but I am achieving 103 MPG.

Theoretical Expenses

My Model S was powered approximately 71% of the time by my solar panels, 28% of the time by superchargers and 1% by other charging systems.  If I were to pay for the equivalent gas costs at $3.5 per gallon, those 40K miles would have cost me $1,358.

A more interesting dollar comparison would be if I had an equivalent ICE vehicle with a rating of 25 MPG.

40,000 miles / 25 miles per gallon = 1,600 gallons

1,600 gallons * $3.5 / gallon = $5,600

The amount of savings driving an electric car is substantial in the long run.

Battery Degradation

At 40,000 miles I have a battery with 6.5% degradation.  Batteries degrade quickly when they are brand new and level off after the initial period.

During my road trip up to Oregon, I also drained the battery down to 17 miles and filled the battery to almost a 100% charge.  When completely charging the battery, my car can sit for over 15 minutes when it is 99% full trying to completely fill up.  I aborted the two attempts to have an absolute complete charge.  The rated range was not increasing although energy was being added at albeit a very slow rate.  I remember when we did the charge-off with the 90kW limited battery, the older battery also exhibited this behavior but not as extremely as mine.  I would at this point consider it a minor issue with the car or the software.

Draining the battery completely and refilling it completely is technically called “battery conditioning”.  Lithium Ion batteries like those in the Model S do not need conditioning and last the longest amount of time when kept at a middle state charge for the majority of time.  The Model S software however can use this data from the endpoints (close to zero and close to full) to more accurately determine the state of the battery.

Here are the exact numbers for my battery:

1. 90% charge
   1. 215 Rated Range
   2. 248 Ideal Range
2. Full charge
   1. 239 Rated Range (265 for a brand new car)
   2. 276 Ideal Range

My numbers are on the low end in comparison to reports from the Dutch survey.  My Roadster also seemed to fall in the same range.  Perhaps the battery likes slightly cooler weather than my garage that only ranges between 50-80 degrees Fahrenheit.