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Old 04-18-2011, 01:26 AM   #57 (permalink)
roflwaffle
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Quote:
Originally Posted by dcb View Post
I do not see where you got %68 at all for electric transportation. (or %75?)

petrol dominates transport, so lets say the product to waste ratio is: 6.74/20.23 or %33.3 efficient at doing work. That is business as usual, averaging the good and the bad. There isn't enough electric signal there to make any speculation about 68.4%

So we have two conversions to consider for electricity. First conversion is the 12.08/26.1, or %40 efficient, without having done any work.

If the stationary homes/industry/commercial are doing mostly things like heating, then the fuel use is going to be very efficient. Those three all rate 80% efficient, regardless of the mix of electric/fossile (possible red flag?) so it isn't a good basis for comparing to transportation (and we want to compare to petrol in transportation because we have petrol pretty well isolated in transportation, and this is a car site).

So we know that electricity from the wall can charge a car, the question is how efficient is that once you do some work.

Well, I think that saying electric cars are %70 efficient is terribly generous, especially "on average", even more so if it includes charging. Remember the goal isn't heat here, it is much more complicated. Regen is a separate issue.

So the two conversions multiplied to gether, %40 x %70, = %28 efficiency for electricity in vehicles. Compared to %33 for petrol transportation. Even if the transportation conversion step was %80 efficient for electricity, that would only be %32 efficient, still less than petrol overall (not counting wars and yadda).
I think we need to differentiate between the efficiency of oil used on personal transportation in a compact car versus the efficiency of oil used in transportation in general, and even the efficacy of oil used in transportation. For instance the efficiency of an SUV at 80mph on the highway is going to be fairly high even if it has poor efficacy. The flow-chart also doesn't show the energy inputs to industry that end up being used to refine oil, it just stops at industry. Supposedly road load plus charging is ~75% efficient for something like the AC-150, so a large manufacturer may actually do better, but in any event I think 70% for EVs is pretty reasonable.
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