eco: CO2 savings with a Tesla

June 8, 2019

tldr;

CO2 emitted from Model 3 last month 287 lbs
CO2 emitted from a 40 MPG car driving the same distance 860 lbs
CO2 saved 573 lbs
CO2 savings rate compared to a 40 MPG car 334 lbs/1,000 miles
CO2 cost of manufacturing the battery, assuming a 200,000 mile battery life 78 lbs/1,000 miles
CO2 savings rate compared to a 40 MPG car, counting battery manufacturing. 256 lbs/1,000 miles
Lifetime CO2 savings compared to a 40 MPG car 25.6 tons

Our electric bill went up by 400 kWh because Tesla.

Last month, our electric bill rank dropped from an excellent 300 kWh used to a way-above-average 700 kWh used. This is because we bought a Tesla, and I was curious how many pounds of CO2 we saved.

CO2 emitted from producing 400 kWh

The 2017 ISO New EnglandElectric Generator Air Emissions Report contains the following data:

Pollutant 2017 lb/MWh
NOx 0.30
SO2 0.08
CO2 682

So, in 2017, generating 400kWh of electricity emitted 273 pounds of CO2.

This seems like an upper bound because

  1. These emissions only count native generation, and thus do not factor in the 14% of our total load that is met by Hydro imported from Quebec and New Brunswick.
  2. Emissions / MWh is going down; for example, from 2016 to 2017 there was a 3.9% decrease in carbon emissions per MWh.

CO2 emitted by an ICE travelling the same distance.

The Tesla Model 3 is rated at 250 Wh / mile. I'm doing a bit better, averaging 233 Wh/mile since I bought the car. So 400 kWh represents 1,717 miles.

In 2018, Toyota Camry was the best selling sedan in the US (178,795 cars sold), followed closely by the Honda Civic (176,242 cars sold). Let's compare with the Civic to give the ICE side the best chance.

A 2018 Honda Civic is 32 city / 42 highway. Taking a swag of 40 mpg on average, 1,717 miles represents 43 gallons of gasoline. Burning a gallon of gasoline emits 20 pounds of CO2, so this distance is 860 pounds of CO2.

Wait, what about electricity transmission losses?

The U.S. Energy department's estimate is that we lose 5% in transmission and generation. Adding 5% to the EV total, we get 287 pounds of CO2.

What about manufacturing CO2?

The best report I have found on this topic is Cleaner Cars from Cradle to Grave, published by the Union of Concerned Scientists in 2015. Looking at Figure ES-2 closely, we can see that the main difference between the CO2 manufacturing emissions is battery, and they estimate that manufacturing a 265 mile battery is equivalent to emitting 32 grams of CO2 per mile over a 179,000 mile lifetime.

This translates to 12,644 pounds of CO2 for the battery. I have a long range battery (325 miles), so scaling this up linearly gets me to 15,507 pounds.

My battery warrantee guarantees the battery will retain at least 70% of its capacity at 120,000 miles. I'm expecting better than that; what people have found with the S and the X is that capacity drops 5% over the first 10,000 or 20,000 miles and then levels off to drop another 2% or so up to 100,000 miles. The model 3 has a more modern battery pack, so I would expect only a 7% degradation at 100,000 miles.

Musk has claimed the Model 3 battery should last between 300,000 and 500,000 miles, which would be great, but for this writeup, I'll assume the battery pack will last for 200,000 miles.

At a 200,000 mile battery life, the manufacturing CO2 works out to 78 additional pounds of CO2 per 1,000 miles travelled.

Summary

If my math is right, over a 200,000 mile lifetime, I'll save 25.6 tons of CO2 emissions compared to a car that gets 40 MPG. And I'll have a lot more fun driving those miles. :)

Solar Panels?

I drive around 20,000 miles a year. Today's price of a Tonne of CO2e on the California Carbon Dashboard was $15.10 per tonne. A tonne is a metric ton, and is 2,204.6 pounds, instead of the U.S. ton, which is 2,000 pounds.

In five years of driving, the current market value of getting electricity from solar panels instead of the grid is 5 * 20 * 287 = 28,700 pounds CO2 = 13 tonnes CO2 = $196 dollars. This market is not pricing this externality anywhere close to the costs associated with global warming. Probably due to the political compromises that had to be made during the market design but that's a total guess. But that's another issue for another blog post.