In the world of gas cars we have a well-accepted metric for understanding a car's efficiency:  Miles per Gallon (MPG).  MPG is often used to get a general sense for how "expensive" a car will be to operate.  (e.g. "35 MPG is pretty good......5 MPG is pretty bad.")  It also is used to compare the efficiency of two cars.  However in the world of electric cars this metric obviously doesn't make sense, as there are no "gallons of gas" in an electric car.  

The Electric Vehicle industry has developed a metric they hope will be an equivalent to MPG:  Miles Per Gallon Equivalent (MPGe).  The thought process goes like this:  One gallon of gasoline contains the same energy as 33.7 kWh of electricity.  Therefore, if an electric car can travel 100 miles on 33.7 kWh of electricity, it would have an efficiency of 100 MPGe.  This methodology can be used to compare the relative efficiency of two electric cars.  But it doesn't help gasoline car owners get a sense of the operating costs of an electric car.   Our electric car has an MPGe of 117 city and 131 highway.  I don't know about you - but that data doesn't help me understand whether operating this car will be "expensive" or "cheap".

We took delivery of our electric car on Dec 8, 2021.  Through Jan 31, 2022 we've driven 635 "local" miles (i.e. errands and other trips close to home).  We also drove 2,911 miles over 9 days during a trip to CA and back.  The following cost comparison excludes that road trip - since that was not "typical" driving for us.

Gasoline Vehicle Cost
Our electric car replaced a 2019 GMC Terrain.  The Terrain typically got about 25 MPG in city driving.  635 miles would require a little over 25 gallons of fuel.  At $3.34/gal - that's a fuel cost of $83.50.

Electric Vehicle Cost
We charge our car using electricity from two sources.  Our preferred power source for car charging is our solar panels.  If we're not able to get the power we need from solar we pay for power from our electric company - like we do when we use any other electric appliance in our house.

Driving the 635 of in-town miles required 301 kWh of electricity.  251 kWh came from the solar panels.  50 kWh were purchased from the electric utility.

The 251 kWh from solar that went into the car weren't "free".  If we had returned that power to the utility (sold it to them) we would have received $15.06 of credit toward our electric bill.  The 50 kWh we purchased cost us $3.50.  Therefore, the energy needed to drive those 635 of in-town miles cost us $18.56.  This, of course, does not include other costs of gas cars such as oil changes, etc.  Including those would make the difference even more dramatic.

$83.50 for gasoline vs $18.56 for electricity - to drive 635 miles.  On a per-mile basis the electric car costs us about 22% of the cost of a gasoline vehicle.

Not everyone has solar panels.  So what would the energy for the 635 miles cost if all of it had been purchased from our utility?  $24.57.  Still - considerably less expensive than gasoline-based transportation.

​Jim

Sometimes technology utterly stuns me.  The first time I downloaded an album from the comfort of my couch is one instance.  Receiving a phone call in the car for the first time is another.  The most recent example:  A car having an API and what can be done as a result.

The first few hours of learning to use the Tesla API were pretty frustrating.  My "Hello World" program was a few lines of code to honk the horn.  After an hour or two I got it to work:
Wife:  "What was that?"
Me:  "That was the sound of Python talking to the car!"

A program talking to a car was the first stunning event.  The second came when I used a simple "Get Status" command and saw what was returned.  Listing all of the information here would make this post too long.  But examples of available car data include:  GPS coordinates, battery charge level, odometer reading, cabin temperature, status of each of the 5 seat heaters, is someone sitting in the driver seat....and on...and on...and on.  

The final stunning event:  The Tesla is connected to the internet all the time.  So getting this data, as well as the ability to control various car functions, can be performed wherever the car is.  Before learning the detailed capabilities of the API I figured, when checking if the car was home, I'd attempt a ping on the local network.  But instead Suncatcher checks the car's GPS coordinates to determine if it's in the garage or not.  

• Your car gets stolen?  Track where it is.  Start honking the horn and flashing the lights.
• Don't like the charging control offered in the Tesla app?  Write a program to do what you want.
• Want more flexibility in scheduling when the cabin warms up or cools down prior to departure?  Write a program to control it the way you want.
• Want reminders of tasks you want to do at certain mileages?  Write a program to check the odometer and alert you when it reaches a specific value.

Amazing!
​
​Jim

For those interested in learning more I'm using TeslaPy:                                                   ​https://github.com/tdorssers/TeslaPy

A few weeks ago I wrote of a project I was starting that would adjust the charging rate of a Tesla based on the electric production coming from solar panels. The goal is to "capture" excess solar being produced (i.e. power that normally would be sold back to the utility) and direct it to the car. There are two drivers for this goal:

• Power our vehicle using electricity that was not produced by the burning of other fuels - such as natural gas, oil or coal.
• Develop a deep understanding of our auto's electricity requirements in order to make a decision to add (or not add) solar panels to our current system.

Since "excess power" can vary widely through the day (solar production can change based on clouds, weather, etc.; and in-house consumption varies as well with tasks such as cooking, laundry, etc.) some form of automated solution is desired to respond to these variabilities and adjust the car charging rate as needed.

The First Half Of The Solution
Prior to the car's arrival I put together some basic code to talk to our Eagle-200 hardware device.  This little box connects wirelessly to our smart (electric) meter and reports whether electricity is flowing to the grid or being pulled from the grid. This is the key information that is required when deciding if the car charging rate should be increased or decreased.

The Second Half Of The Solution
Now that we've taken delivery of the car the second half of the solution has been able to be put into place: communicating with the car using Python. Initial interactions with the car's API was a fascinating experience all on its own. The amount of car information accessible via the API is simply astonishing. More on this will be written in a separate post. In order to implement this project the Tesla API is being used to:

• Determine where the car is.
• Determine if the charging cable is plugged in.
• Initiate car charging.
• Set charging rate (amps).
• Stop car charging.

After establishing the basics of how to communicate with the car, work could begin in earnest to debug and refine the software.  After about a week of work the software is now in a pretty stable state - successfully changing the rate of car charging based on leftover or "extra" power coming from the solar array.

The images below show (on the left) a graph of solar production on a recent day and (on the right) a graph of car charging (amps) through the day. All adjustments to car charging (including identifying when the car was physically unavailable for charging and restarting charging on its return) were handled automatically by the software.
​

Anyone interested in running this solution is welcome to have it - free of charge. The code needs to be "cleaned up" to make it easy for users to change some settings based on how they would prefer the software to behave (e.g. how often the system checks to see if adjustments need to be made). I will also be putting together some documentation/instructions for getting the system running.

If you wish to be notified when this is ready for distribution please send me an email. I will contact you when it is ready for download. Or watch this site for new blog posts on the topic.

Jim