Running cars on coal is a bad idea: CMU researchers

Energy researchers at Carnegie Mellon University say that if the government’s going to spend tax money in support of cars that don’t run on foreign oil, it should focus on developing plug-in hybrids rather than turning coal into gasoline.

Back in April, I wrote about a couple of startling examples where figuring out a way to “skip steps” in an industrial process served up incredible increases in efficiency. Add another case to the list.

This one’s more of a counterexample, illustrating what a colossally bad idea it would be to spend a lot of money on turning coal into liquid fuel that cars, for example, could run on.

The basic technology is largely proven; the Germans liquefied coal in the Second World War when they couldn’t get enough oil anymore, and the South Africans did it in the 1950s and became heavily reliant on coal-based synthetic fuel when they were embargoed over Apartheid. The U.S. Congress is considering elaborate subsidy measure aimed at following suit. The argument is twofold:

  1. America produces quite a bit of coal, and if it could run cars on liquid coal, it’d be a lot less dependent on oil that comes from people who don’t like America very much.
  2. A lot of congressmen who have a lot of say over the energy-related legislative agenda come from coal-producing states and we wants your money! WE WANTS IT!

The problem, though, is that while you can certainly run cars on liquid coal, it takes a lot of energy to turn coal into something that’ll flow out of a gas pump, and it’s dirty, dirty, dirty along the way.

Carnegie Mellon’s Paulina Jaramillo and Constantine Samaras ran the numbers. They compared the energy required to turn coal into fuel for a traditional car to the energy required to run a plug-in hybrid car that gets plugged into the wall at night, then driven until the battery’s dead and the power supply is switched to gasoline. They used middle-of-the-road assumptions about efficiency for both types of vehicle (actually, they assumed the traditional car gets 35 miles to the gallon, which is somewhat generous — it’s the fuel-efficiency standard the Big Three are begging Congress not to set as the average for all the vehicles they sell), and used middle-of-the-road assumptions about the sources of electricity. They didn’t figure the energy for converting coal to oil comes from coal plants and the energy to run the hybrids comes from the beating of fairy wings or anything like that.

Indeed, the only questionable thing is using plug-in hybrids as a comparator. There are no mass-market plug-in hybrids available yet, although after-sale conversions aren’t that hard to come by if you’re will to pay. But then, there’s no liquid coal on the market yet, either.

What they came up with is that driving a coal-powered car for a year would lead to total emissions of 14,200 pounds, or about 6.5 tonnes. A plug-in hybrid driven the same way would lead to total emissions of 2,800 pounds, or about 1.25 tonnes.

If you don’t like the assumptions, Jaramillo and Samaras figure that jigger the premises as you will, a traditional car would need to get 69 miles to the gallon before catching up in efficiency to a plug-in hybrid.

The key point is that taking coal and burning it to make electricity and storing it in a battery that runs a car is vastly more efficient and cleaner than taking coal and burning it to make electricity to take other coal and make it into fuel that runs a car.

The paper’s available from Carnegie Mellon’s Electricity Industry Center, although for reasons I’m not at all clear on, given they sent out a news release about it, it’s password-protected. Some judicious Googling reveals the Username you need is ceicpaper and the password is EnergyResearch.

If the link fails, let me know and I’ll repost the paper myself.

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2 responses to “Running cars on coal is a bad idea: CMU researchers

  1. The best plans for liquid coal call for carbon sequestration or the use of nuclear power at the refinery. If that happens, the dirty co2 problem goes away. We only have around 30 years left on conventional oil, and there will be 9 billion mouths to feed. We need to be open to all the options if we expect human life to continue on this planet.

  2. Pingback: building cars that run on coal - Bad Astronomy and Universe Today Forum

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