Marginal power

[Jason S]

10 gallons of gas at 33kwh equivalent per gallon is 330kwh. The entire petroleum chain from well to tank is about 80% efficient, so that means 20% is used to produce the final product, so the 10 gallons took 66kwh of energy, (not electricity). Now don't forget that the 85kwh's of electricity in a battery pack started out as a lot more energy than that using a generous 40% generating efficiency, (marginal power is probably lower), plus 93% transmission efficiency, a generous 90% charging efficiency, and not to mention the drilling/mining energy inputs, which I don't have the figures for. You have to apply equal criteria for all inputs when comparing gas to electricity.

I've figured out what bothers me most about these figures: 33kwh equivalent per gallon.

How did that number get figured? I know of no way to convert 1 gallon of gasoline to 33kwh of electricity. There are enormous losses involved in any conversion of gasoline to electricity so the number must be something like the amount of work a gallon of gas can do ... like power a car. If that's the way the equivalency is developed then no wonder all the math ends up with them equivalent. You come up with a more efficient car than the average car the equivalency was developed on and bingo, the more efficient car is more efficient.

[Norbert]

I've figured out what bothers me most about these figures: 33kwh equivalent per gallon.

How did that number get figured? I know of no way to convert 1 gallon of gasoline to 33kwh of electricity. There are enormous losses involved in any conversion of gasoline to electricity so the number must be something like the amount of work a gallon of gas can do ... like power a car. If that's the way the equivalency is developed then no wonder all the math ends up with them equivalent. You come up with a more efficient car than the average car the equivalency was developed on and bingo, the more efficient car is more efficient.

The number is 33.7 kWh (EPA), and while I don't know exactly how it is measured or calculated, I expect it to correlate to the amount of heat (=energy) you get when you burn gasoline as completely as possible. Most of the inefficiency in a car is lost as heat (and friction, which also becomes heat).

[stopcrazypp]

I've figured out what bothers me most about these figures: 33kwh equivalent per gallon.

How did that number get figured? I know of no way to convert 1 gallon of gasoline to 33kwh of electricity. There are enormous losses involved in any conversion of gasoline to electricity so the number must be something like the amount of work a gallon of gas can do ... like power a car. If that's the way the equivalency is developed then no wonder all the math ends up with them equivalent. You come up with a more efficient car than the average car the equivalency was developed on and bingo, the more efficient car is more efficient.

33.7kWh represents the energy contained in a gallon of gas (as specified by the EPA: http://www.fueleconomy.gov/feg/evsbs.shtml). It would be what you would get if you were able to convert a gallon of gas to electricity at 100%. You will see slightly different numbers (energy in a gallon of gas varies with temperature, pressure and the specific mix you get), but in general that number is correct.
To figure that number out you use something like a calorimeter:
http://en.wikipedia.org/wiki/Calorimeter

Gasoline refining efficiency is 89.7% (including all products), 86.2% (excluding less desire-able products). So what JRP3 says in general is correct (can't assume energy used to refine a gallon of gas can be used to power an EV for the same miles).
http://www.transportation.anl.gov/pdfs/TA/635.PDF

In general for such energy comparisons, the GREET model is the best resource (uses unbiased methods and examines the entire fuel chain):
http://greet.es.anl.gov/

[JRP3]

Right, we aren't looking to actually turn the gallon of gasoline into electricity, just using the potential energy value to calculate production losses.