Tuesday, July 15, 2008

cars without carrying fuel

It occurred to me while driving home today that part of the advantage of trains powered by electrified tracks is that they aren't weighed down by their own fuel, in contrast to a car. I imagine one day we could have roads that are able to safely provide power to the cars driving on them, removing the necessity of carrying heavy fuel that reduces efficiency. The roads would have some sort of transponder system that logs how many miles your car drove on them and the amount of electricity that you used, and you would pay for that amount like a utility.

I have no idea if we'll have plug in electric cars become the dominant mode of transport, or hydrogen fuel cells or something even more esoteric. It occurs to me that as plug in cars became more popular, the price of electricity would increase, by simple principles of supply and demand.

But energy used on a standard municipal electricity grid is much more efficient than the energy produced in the average internal combustion engine, or so I'm told; and I doubt that even with increased demand the price increase in electricity would create parity with the price of driving a conventional car. The Tesla Roadster, last time I checked, gets something like the equivalent of 100 mpg. Electricity prices would have to go way up before that stopped being a fantastic equivalent. (Lest I ever portray myself as a materialism-hating saint-- I want one. Oh, how I want one. And, it's true, the environmental benefit is a small fraction of the reason for my longing.)

Here's my question: would increased use in electricity (for powering cars) necessarily result in decreased efficiency in terms of carbons produced per mile of travel? I can't imagine why it would, but then I'm probably about as ignorant on this question as I can get. (Sorry for posting this anyway Dave!)


Rob Lyman said...

Short answer: not in principle, but slightly in practice. The issue is daily variation in demand. Electricity must be produced at the moment it is consumed, and at peak times, lower-efficiency (but lower cycle time) plants are turned on to back up the efficient baseload generators.

If the daily commute made the daily swings in electricity use larger, then it could plausibly reduce efficiency somewhat by requiring more fast-cycling peaking plants. The effect, however, would be a tiny fraction of the gains from not using internal combustion engines, which are doomed to permanent low efficiency.

Jordan said...

This is one of the stated advantages of plug-in hybrids: most of the charging will occur during the night, when the load on power stations is normally low. Thus electricity that might otherwise be wasted is being utilized.

Also, the Tesla Roadster is seriously hot. A Lotus with insane torque and a five digit redline? Yes, please.