Eschew Obfuscation: Easy CO2 Calculation for Vehicles

Easy CO2 Calculation for Vehicles

Max Dunn — Fri, 06 Jun 2008 17:05:00 -0700

Sometimes you will hear that electric vehicles produce more CO2 than gas vehicles, however, this isn’t true. Let’s look at an easy CO2 calculation to see why.

Burning a gallon of gas creates 20 lbs of CO2. So a car that gets an average of 20 MPG produces 1 lb of CO2 per mile. Ok so far?

Electric cars get an average of 3 miles per kWh and 1 kWh creates an average of 1.3 lbs of CO2. So an electric car produces about 0.4 lbs of CO2 per mile. So electric cars produce only about 40% as much CO2 as gas cars. Easy, right?

"Easy CO2 Calculation for Vehicles" by Sage

Mon, 05 Jan 2009 17:41:33 -0800

Ha! I had to read your entry several times to figure out why I was puzzled—I inverted the units.

It drives me crazy I’ll read something about a battery capacity, but the author often doesn’t say whether that is the full charge (which isn’t available), or the rated depth-of-discharge for the battery. Most studies indicate 80% D-0-D. Do you know if the 27kw battery is 27 overall? Or 27 available before recharge is needed?

Regional energy generation where I live makes the CO2 savings questionable. :( I embarked on a study assuming I would see a big CO2 reduction. I may still be wrong – it is really dependent on the upstream coal emissions. I’m a huge proponent of PHEV or EV, especially as it ushers in a market for renewable energy. With all those batteries available for storing wind-generated power, a big issue with renewables is eliminated. And of course, those same batteries can be available for ancillary grid service – which doubles the CO2 savings by removing the need for that supply.

Thanks for the explanation.

"Easy CO2 Calculation for Vehicles" by Max Dunn

Sun, 04 Jan 2009 22:01:30 -0800

Glad you found this information useful Sage. :-)

For real-world electric vehicle numbers, I like to look at the RAV4-EV since these have been on the road for 10 years and there are about 300 still being driven.

The raw figures for the RAV4-EV show a 27kWh battery pack that can power the car 100 miles. So this would give it about 3.6mi/wKh from the battery. From the wall, you have to count in the losses in the charger and the batteries. Assuming both are about 90% efficient, this gives us just about 3mi/kWh from the wall.

Some tests of RAV4-EVs showed that the 3mi/kWh applied in the city, but on the highway it was more like 2.5mi/kWh.

I hope this helps!

"Easy CO2 Calculation for Vehicles" by Sage

Sun, 04 Jan 2009 21:35:19 -0800

THANKS A TON for this blog entry. I had been combing the internet for hours trying to find regional data on CO2 emissions per kwh from coal plants. I’d seen your reference before, but it was truncated and didn’t include the regional data. I could kiss you.

I was wondering where you got the 3mi/kWh figure. I’ve seen/figured anywhere from .21 mi to 3+ mi. How did you figure it?