# Coal Fired Teslas

The electricity flowing from a charging station doesn’t magically appear. It must be generated and transmitted to the charger.

Let’s do a bit of analysis.

Looking around the interwebz, I found that the typical Tesla uses 34 kWh of energy to go 100 miles. I’m more used to dealing with energy calculations in joules. 34 kWh = 122 MJ. That’s megajoules.

The typical charging station has an efficiency of about 90 %. In order to deliver 122 MJ to the Tesla’s battery, it will draw about 136 MJ from the power line. The typical efficiency of the power grid from generating station to end user is about 89 %. Some power station needs to generate 153 MJ to get 122 MJ into the Tesla’s battery.

Let’s assume it’s a modern coal fired plant. The efficiency of the process of burning coal to heat water to make steam to turn a turbine to spin an electrical generator is typically around 32 %. That means we need 472 MJ of energy from the coal.

Burning a ton of coal delivers about 22 GJ (gigaojoules) of energy, so we’d need to burn about 43.4 pounds of coal to charge a Tesla to drive 100 miles. That gives a fuel economy rating of 2.3 miles per pound of coal, and that’s roughly equivalent to 15 mpg for a gasoline vehicle.

YMMV

## 1 thought on “Coal Fired Teslas”

1. What would the numbers be for a nuclear plant? I ask because seeing the mpg equivalent for a nuclear plant vs. a coal power plant might help put hard numbers to the foolishness of the people who oppose nuclear yet call themselves “Green”. (And I don’t know how to easily find those numbers myself).