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Marginal power
- Thread starter eledille
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- Energy Environment Policy
Why does electricity get counted at marginal rates when gas gets counted at average rates? After all - if one buys an EV, one should assume that they are reducing gas consumption at the margins and should be credited the marginal emissions of gasoline production. So as you say "you have to apply equal criteria for all inputs when comparing gas to electricity".
Oil sands (certainly could be considered marginal since it's so expensive to produce) have at least a 20-40% higher energy inputs than "conventional" oil. Deep oil, shale oil all require increased energy inputs. Old oil fields require increased energy inputs - water cut gets higher, flow rates go down, etc.
JRP3
Hyperactive Member
I think oil sands do get an extra 20% hit, and Glenn includes that in his analysis. But I also gave marginal electricity an efficiency pass by using 40% which is closer to grid average.
I asked for amount of energy to create 10 gallons of gasoline and I get the following.
Ok, assuming 10 gallons of gas took 66kwh of energy to create we then compare to a 85kwh battery. Net difference is 19kwh. Maybe the battery took 100kwh to charge to that level. Net difference is 34kwh. Or 1 gallon of gas...
So how is burning 1 gallon of gas energy equivalent more than burning 10 gallons of gas?
Please forgive me if I'm just not understanding. You are saying that gasoline's equivalency in electricity is 33kwh for each gallon then backfiguring the energy to create it as 20% of that figure. Why is gasoline 33kwh per gallon? Where'd that number come from?
Ok, assuming 10 gallons of gas took 66kwh of energy to create we then compare to a 85kwh battery. Net difference is 19kwh. Maybe the battery took 100kwh to charge to that level. Net difference is 34kwh. Or 1 gallon of gas...
So how is burning 1 gallon of gas energy equivalent more than burning 10 gallons of gas?
JRP3
Hyperactive Member
A gallon of gasoline has the equivalent of 33-36kwh's of energy in it, I used the lower number. You didn't finish the calculations though, to get 85kwh's of electricity into a battery from the coal mine or gas well takes a lot more than 100kwh's, you left out all the conversion losses I mentioned. You lose more than half the original potential energy along the way, so you'd have to start with more than twice the final 85kwh's.
Norbert
TSLA will win
Those emissions are not the ones they are talking about as being "higher than thought". (Although it appears he did include (at least some) refining CO2 other than that).
EDIT: To be more specific, as far as I can tell, that study appears to show that tar sand oil increase the Prius' emissions from 224 g-CO2/mile not only to 280 g-CO2/mile, but more than that.
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Norbert
TSLA will win
The 40% (modern technologies are higher) do not play into the CO2 numbers either, since that's already accounted for by the 610 g-CO2/kWh which he uses for NG.
In California, night time marginal emissions are (according to the 2009 study) around 575 g-CO2/kWh if you need 4 hours of charging (or 568 g-CO2/kWh if you need 2 hours of charging, and choose the best time in each case). (While NG tech is improving). His NG value for the Leaf assumes higher fast-charging losses of 25%, if instead you assume night charging with NG that is according to his numbers 10% instead.
His best-case calculation is for fast-charging NG: 0.34 kWh/mile * 1.25 * 1.06 * 610 g-CO2/kWh = ~274.8 g-CO2/mile.
However, in California, which has in the order of half the EV sales of the US (so far), night time charging (most common) will be, according to *his* formulas, 0.34 kWh/mile * 1.1 * 1.06 * 575 g-CO2/kWh = ~228 g-CO2/mile.
That's 228 g-CO2/mile for the Leaf in CA, vs. 280 g-CO2/mile for the Prius, according to his numbers for tar sand. Now if it is correct that previous studies "have vastly underestimated the carbon footprint of the Canadian oil sands", then that difference is even "vastly" larger than that, and even worse for the Prius.
Probably the numbers will be similar for other states that use NG for marginal power, such as New York State. I haven't found any data yet about the marginal power of other states, but his assumption that coal is being used for night charging, flat-out, turns out to be wrong.
Me said:
Ok, so the energy costs are double to fill... the 66kwh to create the 10 gallons of gas becomes 132kwh. The 85khw from coal or gas is roughly 2.5x (loses more than half) so it becomes ~200kwh... now we've got 200-132 = 68kwh... ok 2 gallons of gas versus 10 gallons. Hypermiler maybe gets double the milege out of gasoline so we get 2 gallons versus 5 gallons...
Sorry, 2 is still quite a bit less than 5. What am I missing?
Edit: oooh, I see. The doubling metric only counts for some parts of the energy now. Maybe the gasoline costs is already included so 200-66=134 or 4 gallons of gas. Now 4 gallons versus 5 gallons (hypermiler at 65mpg or so) is pretty close but the EV still comes out ahead.
When does the EV get worse? So far we seem to be talking about worst case from my PoV.
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stopcrazypp
Well-Known Member
In that context, it's comparing emissions from a "marginal" part of transportation to the total emissions of all coal and natural gas plants (which power much more than just transportation).
JRP3
Hyperactive Member
No, the 66kwh for the gas includes all inefficiencies and does not get any worse.
Look at it this way, a Prius gets 50 mpg, so from the 33kwh of energy in a gallon to go 50 miles it takes 6kwh's of energy lost to get it into the tank from the well. For the LEAF to go 50 miles at the EPA 330wh/miles takes 16.5kwh's of electricity which took more than twice that to start with so at least 16.5kwh's of energy lost to get it into the battery from the well/mine. Part of the problem in Glenn's analysis results from using a very efficient HEV compared to a not particularly efficient EV, but the LEAF is the best selling EV at the moment so it's not completely unreasonable. I'd love to see what sort of efficiency a Prius EV conversion would get for a direct comparison. I'd do it myself but it would be time consuming and costly to do it right, and I can't justify it just to prove a point.
JRP3
Hyperactive Member
That's a bit of a leap with data from only two states. There are still a lot of states with large amounts of coal power, I don't see how they could avoid using coal, especially at night.
Norbert
TSLA will win
It is not a 'leap', his article claims that coal is used flat-out for night charging, and that turns out to be wrong for *at least* about half of the EVs on the road. Which is enough wrong to say that it is wrong.
As we have seen in LA, "large amounts of coal power" is not at all equivalent to "marginal power". So your statement above is speculative at this point.
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JRP3
Hyperactive Member
No more so than yours. Neither one of us has solid data for how power is provided for specific loads at specific time across the country.
Norbert
TSLA will win
That's why I'm not making a statement "across the country". I'm making a statement "at least about half of the EVs on the road".
Norbert
TSLA will win
I think we are pretty much at the end of the discussion, until someone finds new data (or there is a new article on seekingalpha)
Norbert
TSLA will win
Actually the Leaf's consumption (EPA) seems to be 340 wh/mile, resulting in 17 kWh for 50 miles. If you say you want to double that (perhaps going between older(40%) and newer (60%) tech for NG) for electricity generated by fossil fuels, you have 34 kWh. With transmission 93% (your numbers) and charging 90% efficiency, you get a total of 40.6 kWh.
While I don't know where exactly the 20% number for loss in gasoline's tank-to-well comes from, "even" JP says it is from "transportation, shipping and refining of product", and does not include things like drilling/mining-equivalents either (nor military protection).
But if we take just that 20%, it has to be calculated from the original starting point, which means that if you start with the end product of 1 gallon gasoline = 33.7 kWh (EPA), you'll need to add 25 % = 8.4 kWh, the sum being 42.1 kWh.
So you'd have 40.6 kWh vs 42.1 kWh. You'd have to assume worse than just less-than-50% for fossil fuel generation, for a 50 mpg hybrid to come out better in energy efficiency, in this way of calculating it.
JRP3
Hyperactive Member
Extraction for conventional petroleum extraction is 92% efficient, Alberta oil sands 82-86% efficient, http://fossil.energy.gov/programs/reserves/npr/Energy_Efficiency_Fact_Sheet.pdf
refining 90% efficient,
http://www.transportation.anl.gov/pdfs/TA/635.PDF
Notable is the loss of efficiency projected for the future of extraction.
JRP3
Hyperactive Member
Probably. Please target Norbert if you are so inclined, he's closer to you, fewer emissions from travel.
Norbert
TSLA will win
That's of course missing transportation, pipelines, tankers (which btw produce a lot of CO2), and all those things. And is there some consensus not to use the figure "(with less desirable products excluded)" ? It would seem to me that if we want to get away from oil, we'd also want to exclude any "less desirable products", and that would be 86% instead of 90% by itself.
