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|Embodied Energy Calculation for Electricity
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|Author:||KRoth [ Fri Jun 01, 2007 1:40 pm ]|
|Post subject:||Embodied Energy Calculation for Electricity|
I am using the EIO-LCA tool and am also reading through the book associated with it ("Environmental Life Cycle Assessment of Goods and Services"). I have found apparent inconsistencies in the book when calculating the embodied energy in a kWh of electricity and want to make sure that I am using the correct value for MJ/kWh.
Specifically, in one example, the electricity consumed is added back into the final energy used tally (chapter 14) but it is not in another example chapter 5) Which approach is correct - should one add in the electric energy or not when calculating the total impact of a kWh of electricity conumption? Details of the two examples:
In Chapter 5 of the Book (p.53-54), e.g., for the first washer: kWh/year=2*8*52= 832kWh/year*10 yr = 8,320kWh/life. Using a value of $0.08/kWh, yields $666 of lifetime expenses and, using the value in the model at that point in time of ~100 TJ/$MM, yields the total energy from use only = 0.067TJ=67,000MJ (Table 5-4). ->~8.1MJ/kWh.
In Chapter 14 (p. 142-143): Using a value for $/kWh ($0.069; that is probably a typo - $0.08 would yield the revenues shown) and residential consumption of 1,100,000 MWh, it estimates revenues of $89 billion. Based on the model alone, it multiplied the revenues by ~100 TJ/$MM (the conversion factor in the model back then) to obtain ~9*10^6 TJ. Subsequently - and this is the key difference from the example in Chapter 5 - it [b]added[/b] the electricity consumed in residences, i.e., 1,076,000MkWh (actual EIA value)*3.6MJ/kWh = ~3.9*10^6TJ to the energy calculated by the model to get a total value of ~ 13*10^6 TJ. -> ~12MJ/kWh.
(note: I realize that the conversion for Power Generation & Distribution has changed to ~121TJ/$MM)
In addition, I am attempting to use a solid value for the embodied energy of natural gas. The Ch. 14 example also indicates that the energy value of the natural gas equals distribution + the NG energy itself. It does not appear to, however, include the energy consumed to extract and clean up the natural gas - is that neglected because it is generally much smaller than the other factors? The extraction energy would appear to be part of the embodied energy.
I appreciate any clarification people can offer.
|Author:||marriott [ Mon Jun 04, 2007 2:36 pm ]|
We are in the process of working on the different points in your question. We haven't settled on a full response, but here is some preliminary findings.
So, there are some errors in the book, pg. 142.
1) $89 B implies a value of .081 $/kWh. The correct value should be $75.9 B at .069 $/kWh.
2) When ONLY accounting for the electricity used in the supply chain, the statement made in paragraph 2 of "Use Phase" section is correct - you must add 1.1 BkWh to the 16,300 MkWh* used producing that electricity.
3) The book says 1.1 MkWh in the last line of the 2nd paragraph. It should be "BkWh", but the statement is generally correct.
However, if what you're trying to arrive at is a value for Total Energy, that value is already included in the 10.8M TJ (embodied in the values for coal & natural gas pre-combustion)* and adding the energy embodied in the delivered electricity IS double counting for energy.
* I ran EIO-LCA with $89B in the 1997 PG&S sector
Some of the confusion comes from the fact that Luis' table was not meant to be an accounting table...the numbers aren't necessarily additive. 2nd question: Natural gas extraction is included in the life-cycle energy for natural gas distribution.
Summary and bottom line: There are enough errors in this section that we are double checking the values, but it appears that the approaches in chaps. 5 and 14 are the same, but poorly worded enough to make that non-obvious. More to come...
|Author:||KRoth [ Wed Jun 13, 2007 11:17 am ]|
Joe - Thank you for your reply - I appreciate it!
One clarification: how do you define "Total Energy"? Does it mean "total energy consumed throughout the supply chain"?
Assuming that this is the case, and using following values:
*$90.7B residential electricity revenues in 1997 (from EIA; http://www.eia.doe.gov/cneaf/electricit ... at7p3.html)
*1,076,880,098 MWh of residential kWh sold in 1997 (from EIA; http://www.eia.doe.gov/cneaf/electricit ... at7p2.html)
*121 TJ / $1MM for the most recent Power Generation & Distribution EIO-LCA value
this should yield an embodied energy (i.e., delivered energy + energy for extraction, production and distribution) value per kWh of:
=(90,700 [$MM] *121 [TJ/$MM] * 10^6 [MJ/TJ])/1,076,880,098 [MWh]/10^3 [kWh/MWh] + 3.6 [MJ/kWh] = 13.8 MJ/kWh
Is that correct?
|Author:||hscottm [ Fri Jun 22, 2007 3:14 pm ]|
Sorry for the delay, but we wanted to try to go back as far as possible in the chain of publication for the book and see where we think things went wrong. I apologize in advance to you and others reading this thread since I will go into lots of detail - for the sake of making sure we can all learn from it, and then we can discuss how to "fix" this in the errata for the book on our website.
In short, I think the most important point to make is that the Table 14.1 suffers from a bad job of categorizing flows of energy. The table makes it appear that energy is being double counted, and even just "appearing" that way double counts it even though that wasnt the intent I think. The example in Chapter 5 is "more correct" in classifying things and avoids this confusion.
Note that the book is actually a re-packaging of various papers our research group has written on EIO-LCA, so I went all the way back to the original paper, published by Ochoa et al in ASCE Journal of Infrastructure Systems (December 2002, pp. 132-138), which was then updated for the book. Unfortunately we cannot post attachments of these files in our forums (yet) and so I cannot post them here - I have emailed them to you Kurt to see them (others reading this who are curious can e-mail a request for them).
In the original JIS article, the equivalent of Table 14.1 Kurt mentions (I will call it the BOOK TABLE) is Table 2 (JIS TABLE). Also, the JIS paper used the 1997 annual IO model, not the 1997 benchmark which is currently used on the website (the benchmark wasnt available yet) - thus some numbers are different when running through EIO-LCA.
(For those of you willing to look, this old 1997 annual model is buried in the website at www.eiolca.net/cgi-bin/multimatrix/advindexgerman.pl - it is the 480 sector model for 1997 you can choose to run on that page - but it is old and we no longer really support it)
The most important thing to do is see what the effects of the $89 billion of electricity purchases (1.1 billion kWh) were in 1997. Running that through the old annual 1997 model, you get a TOTAL TJ of energy of 8420000 TJ - found in the same way the new 1997 model does it (adding up primary energy input sources). I note this because running the 1997 benchmark model gives a similar but different number.
The JIS TABLE list the "Use Phase" energy from "Electric services-utilities" as 12 million TJ. If I look at the spreadsheet used to calculate this data point, it adds the 8.4 million TJ from the 1997 Annual model with the 1.1 billion kWh (converted to 3.8 million TJ). The JIS TABLE also then separately lists the 1.1 billion kWh as electricity used (actually as 1.1 million MkWh).
In short, that is where the problem lies (the data point for use phase energy use in the EIO-LCA book - 13 million TJ - looks to have been updated with the 1997 benchmark model results but using the same wrong spreadsheet method of adding the two*). We certainly should not be including the 1.1 billion kWh in both the "electricity" and the "energy summaries" (even if the intent was to separate out electricity from energy, because that is confusing), and more importantly even if we did classify them separately, we should not be adding in the energy value of the 1.1 billion kWh, converted to TJ, in the Energy category, because we're certainly then double counting both the energy needed to make the electricity AND the electricity produced.
I hope this clarifies things. We'll start working on an errata for the text and Table in Chapter 14, and distill this discussion into an errata for the Chapter. I hope you'd be willing to help us double check that errata when we're done Kurt?
* Using the 1997 benchmark EIO-LCA model, producing $89B of electricity uses 10,800,000 TJ of energy across the supply chain
|Author:||KRoth [ Wed Jun 27, 2007 10:37 am ]|
Thanks for taking the time to clarify the electricity-energy analysis.
For me, this also clarifies how EIO-LCA deals with electricity and energy. When I was simply comparing the EIO-LCA "power generation" energy/kWh to EIA values, I was confused because the EIO-LCA yielded a lower ratio of primary energy used to produce electricity to the energy content of the electricity than EIA (which was ~3.2 circa 1997) even though it should have been higher because it included additional life cycle energy (e.g., from extraction, transport, distribution, etc.). Understanding that the EIO-LCA counts the energy used to generate the electricity (and other energy consumed throughout the supply chain) LESS the actual energy content of the electricity as "energy" and counts the actual energy content of the electricity separately as "electricity" resolves that apparent inconsistency. So, the point in Chapter 14 of the book that to calculate the total energy consumed one must add the electric energy to the EIO-LCA "power generation" energy would be technically correct, but the way it was presented in the table is inconsistent with the accounting process used in EIO-LCA (and, in that form, could readily lead to double counting).
Please let me know if what I have written is incorrect.
I appreciate the offer to review the errata and would be glad to do so.
|Author:||mbendewald [ Fri Jun 06, 2008 11:29 am ]|
|Post subject:||primary energy ratio|
I have a question regarding Kurt's calculation method of a primary energy ratio. I'm noticing significant differences in a primary energy ratio depending on which sector I am looking at. For instance, in 1997 US Industry purchased $47 billion worth of electricity and consumed about 1 billion MWh (both EIA values). The residential sector, on the other hand, spent almost twice as much money on about the same amount of electricity. This makes sense because industry pays a much lower rate for electricity. Accordingly, since the EIO LCA calculator is using the same TJ/USD figure for any purchase, the electricity provided to industries has a much lower primary energy ratio. I would think the ratio should be similar no matter the sector of consumption.
In the Methods document on this website it mentions converting the dollar amounts of electrical purchases to physical units using two separate rates: one for industry ($.043/kWh) and the other ($.076/kWh) for everything else (p 27). I assume that a weighted average of these two rates would yield an overall average conversion coefficient.
Would you advise adjusting total expenditures in each sector based on how close the 1997 rate (USD/kWh) is to the average conversion coefficient? My ultimate aim here is to arrive at a national average primary energy ratio.
|Author:||lifecycle [ Wed Jul 06, 2011 11:44 am ]|
I don't like the idea of combining two variables that have completely different influence. Maybe I am misunderstanding your reasoning? I have been doing a pretty large scale research project studying the life cycles of the molecules they use to make structural foam for construction, etc. there is no way the overseers would let me play with the variables like that.
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