Interesting analysis of electric cars and energy use.

 

From your Digest

Ryan Carlyle

BSChE, engineer at an oil companyUpdated May 7, 2014

If all cars in the US suddenly become electric, how much more electricity do we need to produce (in percentage)?

Let's do the math.

The US burned 133 billion gallons gasoline in 2012. I'm going to ignore diesel vehicles because the majority of diesel burned in the US is in heavy vehicles where battery-electric drivetrains are not a practical option.
How much gasoline does the United States consume?

The average thermal energy content in gasoline is 33.41 KWh/gallon.
Gasoline gallon equivalent

This gives 4,443 TWh of thermal power going to gasoline road vehicles in the US per year. If we assume electric vehicles use energy with 4x the efficiency of gasoline vehicles (a reasonable round number) then it would take 1,111 TWh of electrical energy to replace that gasoline energy.

US electricity consumption in 2011 was 3882 TWh.
International Energy Statistics

So the increase in yearly electricity demand would be ~29%.

Now let's look at what this does to CO2 emissions.

Each gallon of gasoline contains 8,887 grams of CO2.
Calculations and References

So the CO2 reduction from avoided gasoline consumption (assuming demand does not rise elsewhere to compensate) would be 1182 million tonnes CO2 per year. But this is the gross figure before increased electricity use is considered.

If we assume the extra electricity comes from the existing mix of non-base-load sources (as nighttime charging likely would), the CO2 emission per KWh of electricity is 689 grams of CO2.
Calculations and References

Electric Vehicles: Myths vs. Reality

So the total increase in CO2 emissions from increased electricity consumption would be 765 million tonnes Co2 per year. Thus the net CO2 emission reduction would be 417 million tonnes.

Total US CO2 emitted in 2012 was 6,526 million tonnes.
U.S. Greenhouse Gas Inventory Report

So the net decrease in national CO2 emissions would be ~6.4%.

[Update: Graham Katz pointed out that I've neglected the CO2 emissions from refining, which is a valid point. Gasoline's share of US refinery emissions is ~130 million tonnes, which increases the CO2 reduction from ~6.4% to ~8.4%. There are many other factors which can be included in the analysis that will increase or decrease both cost and emissions, and for the sake of brevity, I'm ignoring those. A full accounting would take hundreds of pages.]

Now let's look at cost.

The average US car costs $25,000.
Passenger vehicles in the United States

Electric cars -- pre-subsidy -- are running around $40,000. Now, this will come down with scale. But the "average" $25k car price today also includes many heavy vehicles and diesel-burners that skew up the average price. Small gasoline vehicles that are good candidates for replacement with EVs are cheaper -- perhaps $20k average. So at today's costs, EVs cost $20k more than equivalent gasoline vehicles. But let's be conservative and call it $30k for an economy-of-scale electric vehicle. This means $10k marginal cost over gasoline for a good round number.

So there's two cost cases to consider here. Switching all cars instantly, versus merely replacing all old vehicles with electric cars.

• For the extreme "instant" switch, around 150,000,000 vehicles have to be replaced immediately, and gasoline cars lose all value. That would cost $4.5 trillion.
• For the "gradual" switch, where gasoline vehicles are run until the end of their useful life, you only need to consider the marginal increase in cost over a business-as-usual case. So the cost would be $1.5 trillion.

I think these are fairly conservative numbers. Reality would probably be somewhere between the two.

Taking the $1.5 trillion figure, that gives us an effective cost of CO2 reduction of ~$3600 per tonne CO2 per year. Amortized over 30 year vehicle life (which I think is extremely optimistic in the US) that gives $120/tonne CO2 avoided. This is quite expensive.

To be fair, EVs also have long-term savings in fuel cost but the rest of the math is very conservative so I don't feel bad about neglecting this. Decrease the expected vehicle life to a more realistic number (considering battery longevity), or retire gasoline vehicles more aggressively, and the net $/tonne CO2 number will come out about the same.

I'm sticking with $120/tonne -- I think it is a reasonable estimate. You're welcome to disagree in the comments if you have a better number.

Current industry estimates put the cost of coal power plant carbon capture & sequestration (CCS) at ~$80/tonne CO2 captured. Then that CO2 has an economic value of ~$40/tonne for enhanced oil recovery. So the net economic cost of CCS is ~$40/tonne. (These numbers may not scale linearly, but neither do the marginal electricity and CCS costs. It arguably washes out.)
Journal of Petroleum Technology February 2014 Page 46

Which means electric vehicles are a pretty crummy way to reduce CO2 emissions, given the current US power mix. You can do three times as much good per dollar by fitting coal plants with carbon capture systems. Not to mention even better alternatives like replacing coal plants altogether with nuclear, wind, or combined-cycle gas plants. Mass rollout of electric vehicles is only worthwhile in tandem with massive increases in renewables generation. Perhaps in the future we'll get there. But today's generation market trends do not support that assumption for the next several decades.
U.S. Energy Information Administration (EIA)