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Old 05-02-2009, 12:45 PM   #111 (permalink)
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Quote:
Originally Posted by Ernie Rogers View Post
There is an alternative. I can do this comparison analytically. I just put the parameters for each kind of car into the program.

Here are parameters you could consider--

Gasoline engine efficiency.......30% (to the shaft, good for a Prius)
That's a good example of the sort of thing I was hoping to get away from by using an experimental method. Look at BSFC charts: your gas engine efficiency is going to be all over the place, depending on how you drive. If you just measure things over a drive cycle, you don't have to bother about calculating the differing efficiencies.

Might even want to do several different cycles for comparison: (sub)urban stop & go, freeway cruising, rural roads, etc.

Humm... Anybody on an engineering faculty? Maybe you could get a research grant...

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Old 05-02-2009, 02:13 PM   #112 (permalink)
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There you go again

Why not do the same for the guys who ride bikes
But of course then we would have to know the carbon foot print of the bikers breakfast

"you had corn flakes! that is going to hurt your milage
Wells to pedals man!"

my sarcasm runneth over

Ernie has a point... EVs are not properly accounted for
Ecomodder's "milage displaced" bike meter is clever way to compare the incomparable
EVs have a similar issue - they need their own measuring stick
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Old 05-02-2009, 04:56 PM   #113 (permalink)
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From Concrete:

Quote:
No good answer

I think this thread is proof that there is no good way to compare oil burners & EVs
it is obvious our world views preclude agreement (opinion based math?)
whatever standard you pick will make people mad.

Leave MPG for oil burners and move the EVs to their own standard
Jamesqf said:

Quote:
I think there is a fairly reasonable way to compare: start from the other end and do it experimentally. Find someone (or better, several someones) who've done EV conversion on say a Geo Metro. Find the same model that's unconverted, have them both drive a measured course keeping same speed &c, and for best results swap drivers in the middle.

Divide gallons used by KWh used, and there's your conversion factor. You can use that to work backwards through the supply chain to get total efficiency.
In my post, I suggested using pump-to-shaft efficiencies of 70% for an EV and 30% for a gasser, with all other parts equal, and then we can calculate the conversion factor.

From DCB:

Quote:
I don't *think* I need a program to show me how to multiply by 3/7ths, but thanks anyway Ernie.
(And, of course, he's right—I could have thought of that!)

At that point, Jamesqf and Concrete started to wander outside the box.

Okay, there are some good ideas here. So, what if we follow Jamesqf's idea, combined with dcb's response? Let's have a gasser and an identical EV drive a distance so that the gasser uses one gallon of gas. The EV will use only 3/7 as much energy, or

(34 kWh for a gallon) x 3/7 = 14.57 kWh

So, Jamesqf, there's your conversion factor--

1 gallon of gasoline = 14.57 kWh

Nope, the electric boys wouldn't accept that.

If we had included the losses from well to pump /mine to plug, the overall efficiencies would be--

Adding in:
Average utility: about 40% (Wang gives 38.1% for U.S. average, to plug)
Average refinery: about 80% (From Wang, from 79% to 82%, to pump)

Gives:
EV...........0.40 x 0.70 = 0.28
Gasser.....0.80 x 0.30 = 0.24

So, overall from well-to-wheels, an EV is 28% efficient and a gasser is 24%. (Based on all the assumptions. Somebody will surely disagree.)

Then, the conversion factor is--

34 kWh/gal x (.24 /.28) = 29 kWh per gallon of gasoline

What do you think, would people agree to this conversion? It means that if the EV and the gasser have equal mpgs, then the two cars use exactly the same amount of energy, counting all steps from the mine or well to the wheels.

Ernie Rogers
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Old 05-02-2009, 05:54 PM   #114 (permalink)
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Quote:
Originally Posted by Ernie Rogers View Post
Let's have a gasser and an identical EV drive a distance so that the gasser uses one gallon of gas. The EV will use only 3/7 as much energy...
Will it? Your theoretical computations might be right on the money (for a reasonable drive cycle), or they could be way off in either direction. We won't know for sure until someone actually does the experiment.
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Old 05-02-2009, 09:51 PM   #115 (permalink)
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Quote:
Okay, there are some good ideas here. So, what if we follow Jamesqf's idea, combined with dcb's response? Let's have a gasser and an identical EV drive a distance so that the gasser uses one gallon of gas. The EV will use only 3/7 as much energy, or

(34 kWh for a gallon) x 3/7 = 14.57 kWh

So, Jamesqf, there's your conversion factor--

1 gallon of gasoline = 14.57 kWh

Nope, the electric boys wouldn't accept that.
I can't put my finger on it - probably because I've only spent the time it took to read the post thinking about it...

That suggests that a higher efficiency EV in the experiment, what should be an independent variable, results in less energy in a gallon of fuel. This makes my intuition gland tingle.... It not sitting well with me (just yet) from a conservation of energy stand point.
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Old 05-02-2009, 10:47 PM   #116 (permalink)
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This does sound funny on the face of it.

I said,

Quote:
Okay, there are some good ideas here. So, what if we follow Jamesqf's idea, combined with dcb's response? Let's have a gasser and an identical EV drive a distance so that the gasser uses one gallon of gas. The EV will use only 3/7 as much energy, or

(34 kWh for a gallon) x 3/7 = 14.57 kWh

So, Jamesqf, there's your conversion factor--

1 gallon of gasoline = 14.57 kWh

Nope, the electric boys wouldn't accept that.
And, you replied--

Quote:
Originally Posted by trebuchet03 View Post
I can't put my finger on it - probably because I've only spent the time it took to read the post thinking about it...

That suggests that a higher efficiency EV in the experiment, what should be an independent variable, results in less energy in a gallon of fuel. This makes my intuition gland tingle.... It not sitting well with me (just yet) from a conservation of energy stand point.
Excellent thinking, Tre,

Let's see if we can figure out what's wrong here. I think we have to understand Jamesqf's goal in setting this up. Maybe James is listening. He said to himself, "look, if two cars have identical efficiency in every respect except one is a gasser and the other is an EV, then why not say they have the same mpg or equivalent?" What we are doing is taking out of the comparison any natural advantage for either the gasser or the EV. Provided we can agree on what a "normal" gasser or EV power plant is capable of, this should work. I guessed the "normal" efficiencies for the gasser and the EV:

Gasser.......30% pump to shaft
EV............70% plug to shaft

And said in a loud voice that the vehicles are otherwise "the same."

From that, I got that such identical cars will have identical mpgs if we set the conversion to 1 gallon of gas = 15 kWh (for round numbers).

Okay, these were "normal" cars. If a gasser comes along that does better, getting say 40% from the engine, and a really low drag coefficient, and regen braking, then it will show a higher mpg. Likewise, if the EV is more efficient than the norm, say with a power transfer efficiency of 90%, and especially efficient body design, then it will score a higher mpg. (The conversion factor remains at 15, no matter how good the EV is.)

Phew, that was hard. You know, I am beginning to really like James' idea.

Ernie
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Old 05-03-2009, 02:29 AM   #117 (permalink)
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Quote:
Originally Posted by Ernie Rogers View Post

And said in a loud voice that the vehicles are otherwise "the same."
Everything is the same, except the drive trains (we'll assume identical transmissions)... The Gasser is obviously not going to have a charger. And as the charger is 1 of a few points of power loss (motor, controller, batteries, charger, et. al.), moving to a more efficient charger changes the total efficiency and the car is arguably otherwise "the same" as our Gasser counterpart.

For whatever reason, proportional efficiency isn't sitting well with me. I think the experimental setup has potential (pun intended if you want ), however. Execution of the experiment would be difficult I think - as we're measuring energy (a timeless unit), it's totally possible to drive the vehicles in a different manner as long as they're on the same course.



It's late, I'll put more thought into it after sleeping
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Old 05-03-2009, 05:14 AM   #118 (permalink)
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Personally I'd be in favour of a second listing for EVs. In Wh/km or kWh/100km (the latter as it is similar to the metric L/100km measurement. I also think that the figures could be displayed in either metric or imperial based on your user settings, but that's another topic.

As far as the actual efficiencies. If you go any further than wall-to-wheels (or bowser-to-wheels) it gets awfully tangled. I'll leave it to the smarter people to sort it out. Though I note that my own EV will (eventually) be run on my own electricity generated at home. Most likely by solar, though only if I'm not allowed to put a wind turbine on my roof. Though I will concede that I'll most likely have a diesel generator backup just in case. The last thing I want is to have to call in sick to work because the power went out! haha
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Old 05-03-2009, 11:56 AM   #119 (permalink)
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Well to Wheels greenhouse gas equivalence: 15.2KWh = 1 gal gasoline
Well to Plug/Pump energy equivalence: 34 KWh = 1 gal gasoline
Cost equivalence: 18.5KWh = 1 gal gasoline for me today. Wildly variable, changes daily, different everywhere.

Data from Ernie Rogers' post #85, cost equivalence based on $.12/KWh and $2.25/gal.

So, are you worried about running out of sources of energy, or global warming, or money in your pocket? I don't think it's Ecomodder's place to take up a position on that, so EM shouldn't compare KWh to gal, except to say it's between 15 and 34 KWh/gal.

Not only would it be difficult/impossible to agree on a single KWh to MPGe conversion factor, but it wouldn't be a good idea to boil down EV vs gasser to a single number. They do different things. I'd venture that current-gen DIY electrics are driven shorter distances at lower speeds, and very few of them can complete a road trip. But electrics offer a chance at self-reliance if combined with at-home generation. That applies on a national scale, as well.

I come across as anti-EV at times, and I believe the lifecycle GHG benefits aren't there, but both of those things will change at such a time as the grid shifts to a greener mix and battery technology improves.
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Old 05-03-2009, 01:46 PM   #120 (permalink)
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Guys,

I am greatly impressed with the intellectual quality of posts on this list. It's a distinct pleasure.

Ernie Rogers

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