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Stop this silliness now. Claiming a "miles per gallon" figure when you get significant amount of your energy from another source is just silly. Its like claimin
by jws 19y ago
Stop this silliness now. Claiming a "miles per gallon" figure when you get significant amount of your energy from another source is just silly. Its like claiming 100mpg if you start at the top of Pike's Peak.
I propose we popularize "kilometers per megajoule", or kpm. A gallon of gas has 130 megajoules, 33% efficient internal combustion engine, so a 60mpg car would be something like 2.5kpm. This will nicely separate separate efficiency of motion from energy source. People should be able to easily reason about a 2.5kpm vehicle with a 20 megajoule plugin chargeable battery. (I think, no one has check these numbers. Notice I had to come back and edit for the engine efficiency once already, so they should be scrutinized.)
The ugly part is how to think about the internal combustion engine. You may have 1300 mega joules in the gas tank, but you will lose 60-70% of those in your engine before they meet the drivetrain. I leave that part as an exercise to the reader.
- deleted 19y ago[deleted]
- brookr 19y agoBut from an environmental perspective, perhaps people are more concerned about the trade-off between carbon emissions and distance traveled. Efficiency measures would be great way to evaluate drive sources, and would perhaps be very revealing when internal combustion is exposed as being so inefficient. But perhaps a rating of carbon "moles per kilometer" would be a better indication of environmental impact of any motion source. It would be interesting to compare even with walking, running, and biking (at different speeds), as you exhale (significantly smaller) amounts of carbon dioxide (and none of the worst carbon offender, CO, thankfully). Here too, the energy source that you are plugging this module into could greatly vary your MPK.