Does it help the environment to drive a coal powered Tesla?
If you buy an electric car today, the sad reality is that it’s probably running on coal or natural gas.
A few states are better than average. If you live in Washington state and charge the battery at night, it will probably get charged with hydropower. If you live in California and you charge the battery during the day, it might get charged by solar.
But in half of all states, it’s probably going to get charged by coal, and in the rest it’s going to get charged by natural gas.
Is there any benefit to driving an electric car, even if the batteries still get charged by fossil fuels?
It depends. Let’s do the math:
First Up: Gasoline powered car
A Honda Civic is a boring but functional sedan. It gets 36 miles per gallon of gas (32 city, 42 highway).
It’s a convenient car for either commuting or traveling long distances — the car has a range of 446 miles before you need to fill the tank.
It takes 2.77 gallons of gas to drive 100 miles.
Burning one gallon of gasoline makes 8.88 kg of CO2.
So that’s 24.6 kg of CO2 for every 100 miles.
Next Up: Electric Car
A Tesla Model 3 gets 141 MPGe (148 MPGe city, 132 MPGe highway)
MPGe is “miles per gallon equivalent”. It’s a totally misleading and confusing comparison, because of the way people compare batteries to gasoline.
Burning gasoline makes a lot of energy, but only 20-30% of that energy gets used to power the car, the rest is lost as heat. With an electric car, more like 90% of the energy in the battery is used to power the car, it’s not lost to heat.
On the other hand, the power for your electric car probably comes from burning coal or natural gas. The power plant that burns that fuel loses some of it to heat. If the power plant was an engine that burned gasoline, then the electric car would be no greener than a regular car.
141 MPGe makes it sound like the Tesla is super efficient, but it’s actually just ignoring the losses at the power plant.
The only way to really compare this is to figure out how much carbon that power plant is making.
If the electricity comes from an oil burning power plant, it makes 0.97 kg of CO2/kWh.
The Tesla uses 24 kWh of power to go 100 miles.
So that’s 23.3 kg of CO2. Almost as much as the gasoline powered car.
It’s not really equivalent to 141 miles per gallon, it has the same emissions as if it got 38 miles per gallon.
If the power comes from coal, it makes 1.01 kg CO2/kWh.
So now your Tesla is making 24.2 kg of CO2. The environmental impact is the same as the Honda Civic.
But the Tesla costs twice as much to buy, it’s harder to refuel, and the range between charging stations is only 250 miles. All that inconvenience and the pollution is the same.
If that power comes from natural gas, the Tesla comes out ahead. Natural gas makes 0.41 kg of CO2/kWh.
That’s 10 kg CO2 to go 100 miles. The Tesla makes less than half as much carbon as the Civic. The emissions are the same as a gasoline powered car that got 88 miles per gallon.
I’ve left out the energy loss in charging the car (about 10%) and in the power lines. But I’ve also left out the energy from transporting the gasoline from the well to the gas station. Let’s just call those even.
Which states is the Tesla better for the environment? I tried to estimate from this map of electricity by state:
In the orange states, the Tesla is better because fossil fuel power is mostly from natural gas. In the grey states, fossil fuel power is mostly from coal, so it’s the same as a Honda Civic. Hawaii burns oil, not coal, but the emissions are almost as bad.
A 2015 paper breaks this down further, state by state, and recommends against widespread adoption of electric vehicles on the current grid.
They instead recommend a different option.
What about a hybrid?
There’s a third choice:
A Toyota Prius gets 56 miles per gallon (58 city, 53 highway).
To go 100 miles, it makes 15.8 kg of CO2.
It’s better for the environment than a Tesla, in any state that burns coal.
It’s mostly better because it’s a smaller, more aerodynamic car.
It still doesn’t beat the Tesla run on natural gas. But buying a Prius is a lot cheaper than buying a Tesla. What if you wanted to help the environment with that extra money?
Opportunity cost.
A Tesla Model 3 starts at $40,400.
A Honda Civic starts at $22,250.
A Toyota Prius starts at $25,075.
You could buy a Prius and take the remaining $15,000 to put solar panels on your roof.
6 kilowatts of solar panels would make 900 kWh per month, which is the average household use, so your house would be carbon neutral.
If you live in a state that burns coal, you’re already doing better than the Tesla driver and you’ve also made your home electricity cleaner — you’ve prevented 1,000 kg of CO2 from going into the atmosphere. That’s the same emissions as driving your car 4,000 miles every month.
If you live in a natural gas state, you probably still come out ahead of the Tesla driver. Your solar panels save 370 kg of CO2. If you drive less than 6,300 miles per month, you’ll do more for the environment.
If you can afford a Tesla, and solar panels to charge it, and maybe batteries to store the solar power so you can charge it at night, then I guess you ought to do all that.
Conclusions:
Electric cars may help us avoid peak oil. They will be needed to stop global warming. But they won’t help much if we don’t stop burning coal, first.
We’re probably not going to stop soon, because the swing vote in the senate made millions of dollars from his coal company.
In half the states, a humble Prius is better for the environment than a fashionable Tesla.
If you’re already driving a hybrid, you should buy solar panels before upgrading to an electric car.
If Tesla starts making cars for $25,000 or less, it’s definitely worth buying one, if you live in a natural gas state.
If you live in a coal burning state, you’d still be better off driving a Prius, even at that price.
