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matt

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which is better, electric or gasoline? [Mar. 12th, 2007|02:13 pm]
matt
35 kwh ~= 1 gal gasoline (need good source for this figure.)

35 kwh x 0.6kg CO2/kwh = 21kg CO2
1 gal x 8.8kg CO2/gal = 8.8kg CO2

gasoline would have less carbon footprint by this equivalence. However, it all depends on the first figure, which is from http://baltimorechronicle.com/2005/083005Korthof.shtml I need a better source for the expected range of this value.

update: If an electric engine is about 40% efficient, and a gas engine is about 15% efficient, then the figures are modified:

35 kwh x 0.6kg CO2/kwh = 21kg CO2 / 0.4 efficiency ratio = 52.5kg CO2
1 gal x 8.8kg CO2/gal = 8.8kg CO2 / 0.15 efficiency ratio = 59 kg CO2

So, with rounding errors and other losses, they're in the same order of magnitude in terms of carbon footprint.

update 2: If an EV gets between 2 and 6 miles per kwh, then

8.8 kg CO2 per gal / 20 miles per gallon = 0.44 kg CO2 per mile
8.8 kg CO2 per gal / 30 miles per gallon = 0.29 kg CO2 per mile
8.8 kg CO2 per gal / 40 miles per gallon = 0.22 kg CO2 per mile
0.6 kg CO2 per kwh / 2 miles per kwh = 0.3 kg CO2 per mile
0.6 kg CO2 per kwh / 4 miles per kwh = 0.15 kg CO2 per mile
0.6 kg CO2 per kwh / 6 miles per kwh = 0.1 kg CO2 per mile

I think I was led astray by the red herring conversion 35 kwh = 1 gal in the article. Converting to electric vehicle use depends strongly on the battery power and efficiency of conversion.

I'm very wary of figures I get from enthusiasts, since I know exactly how much my driving style can alter my fuel consumption on a variety of hybrid and non-hybrid vehicles. I also know that I can't always drive ideally.
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Comments:
[User Picture]From: en_ki
2007-03-12 09:35 pm (UTC)
35 Kwh is about $6.33 where I live. That would suggest that, even with gas prices as high as they are, I ought to buy a gas generator and run my house off that instead.

You would think if it were that easy to save 50% on one's electric bill, people would already be doing it.
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[User Picture]From: hbergeronx
2007-03-12 09:53 pm (UTC)
You can't generate 35kwh from a locally installed generator with 1 gallon of gasoline (I think that assumes total conversion!). But the reality is that even if it were as efficient there are noise and CO2 and CO issues associated with generating the power locally.

Some people *do* generate their own power, and I bet they can get power cheaper than $6.33/kwh. But few people would want to make the capital investment and ongoing maintenance costs associated with building your own generator. Plus, there are zoning regs where you live, I imagine.
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[User Picture]From: en_ki
2007-03-12 10:56 pm (UTC)
What I'm getting at is that I don't think that's a comparison of apples to apples: one thing is being rated at a realistic efficiency rating and the other at an ideal one.
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[User Picture]From: hbergeronx
2007-03-13 02:46 am (UTC)
I know the comparison is not accurate- I'm trying to make it better. It's not as simple as the difference between an ideal and a realistic option being compared. There are huge losses associated with electricity, the worst of which is that it cannot be stored. For me, I might go for a few days or so without using my car, and the cost of keeping it charged is wasted. I can put a gallon of gas on the shelf pretty much indefinitely, though.

The point of this is not "if I got my electric from a wind or solar farm, versus if I got my gas from say, saudi arabia", but what the actual incremental, marginal difference would be if I converted from my (fairly efficient) gasoline hybrid to an all-electric vehicle. I think that without major social change, the move would be carbon neutral, and that's what the second number shows. The first number suprised me, and I wasn't sure why it came out that way.
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[User Picture]From: mactavish
2007-03-12 10:19 pm (UTC)
Like Ken's?

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[User Picture]From: hbergeronx
2007-03-13 02:56 am (UTC)
Since about 50% of electric generation is from coal, and a good percentage is from similar fossil fuels like oil and NG, it is not surprising that the value for coal alone is similar to the value for coal in mixture with other sources. It's just the same number, repainted, more or less.

Plus, there are significant non-power-generation uses for coal, such as in steel production and recycling.
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[User Picture]From: hbergeronx
2007-03-13 03:09 am (UTC)
90% of coal is used for power generation in the US. ( http://en.wikipedia.org/wiki/Coal )
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