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Hi all!
Remember this thread on the @IPCC_CH lifecycle emission factor for #coal?
I received an answer from Christopher Oberschelp (thanks!), author of the Nature paper cited in the thread, and I think he solved the mystery.
So here we go.... "IPCC coal factor, take 2!"
https://twitter.com/ThomasGibon/status/1339233410125082626
Remember this thread on the @IPCC_CH lifecycle emission factor for #coal?
I received an answer from Christopher Oberschelp (thanks!), author of the Nature paper cited in the thread, and I think he solved the mystery.
So here we go.... "IPCC coal factor, take 2!"
https://twitter.com/ThomasGibon/status/1339233410125082626
Reminder: the question is
"Why did the IPCC publish a value of 820 g CO2 eq./kWh for coal power, when many LCA studies show a range of 1000-1400 g CO2 eq.?"
This figure was actually from Christopher's paper, and clearly shows that 820 is out of reach. https://twitter.com/ThomasGibon/status/1339233430937231360
"Why did the IPCC publish a value of 820 g CO2 eq./kWh for coal power, when many LCA studies show a range of 1000-1400 g CO2 eq.?"
This figure was actually from Christopher's paper, and clearly shows that 820 is out of reach. https://twitter.com/ThomasGibon/status/1339233430937231360
It all boiled down to a single, seemingly overoptimistic efficiency value of 49% that was used, in what ended up to be the principal data source for the IPCC review.
Problem is, the best averages we see today are neighboring 38%. The gap is staggering.
Problem is, the best averages we see today are neighboring 38%. The gap is staggering.
Thing is, a coal power plant is not a black box, it consists of three main elements, here with their specific efficiencies:
a boiler (86%),
a turbine (Rankine cycle, 49%), and
a generator (98%).
Throw in losses (7%), and you'll get an overall 38%.
(fig C. Oberschelp)
a boiler (86%), a turbine (Rankine cycle, 49%), and a generator (98%).Throw in losses (7%), and you'll get an overall 38%.
(fig C. Oberschelp)
Wait now, 49%? 38%??? Would it be possible that the autho...
Yes. Yes, it seems they did: the authors most likely confused the two efficiency values.
Yes. Yes, it seems they did: the authors most likely confused the two efficiency values.
With an (hypothetical) overall average efficiency of 49%, direct emissions are indeed
94.6 kg CO₂/MJ (avg for coal) * 3.6 MJ/kWh / 49% = 697 g
Plus indirect emissions (~120 g) = 820 g.
With a (correct) overall value of 38%, we have 896 + 120 = ...
1020 g CO₂ eq./kWh
94.6 kg CO₂/MJ (avg for coal) * 3.6 MJ/kWh / 49% = 697 g
Plus indirect emissions (~120 g) = 820 g.
With a (correct) overall value of 38%, we have 896 + 120 = ...
1020 g CO₂ eq./kWh
So that's it.
End of story.
The infamous 820 factor was off by 200 g this whole time and now we know why.
Many thanks to Christopher for the investigation work, and here's hoping that AR6 corrects the gap!
poke @judlj @Thomas_Auriel @maxcordiez
End of story.
The infamous 820 factor was off by 200 g this whole time and now we know why.
Many thanks to Christopher for the investigation work, and here's hoping that AR6 corrects the gap!
poke @judlj @Thomas_Auriel @maxcordiez
