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156 comments on A Net Energy Parable: Why is ERoEI Important?

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step back on August 9, 2006 - 3:17pm

Slaphappy,

IMHO you are correct to recognize that eROI is an accounting game just like $ROI is.

In the case of eROI, if we stoped allowing ourselves to not-count energy inputs that are "free" (don't cost money) then eROI will always be less than unity because of the entropy laws of thermodynamics --all real world transformation processes are lossy and energy is conserved (assuming no E=mc^2 stuff allowed).

However, if we choose to exclude the money-wise "free" parts of the energy inputs and to exclude the one-time energy costs for manufacturing the contraptions (e.g. ethanol plant) used in transformation (e.g. corn to ethanol), then we get some sort of partly-economic, partly-physics measure of the long term payback we get for our efforts.

We can use this eROI number for comparing one type of apples against another, for example, switch grass ethanol versus corn ethanol --which has higher eROI assuming conversion plants for each are equal?

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slaphappy on August 13, 2006 - 2:14pm

I'll grant you most of that (and the E=mc2 stuff doesn't really pose a problem, matter is nothing more than "frozen" energy anway), but the comparison between switchgrass and corn, I don't agree with.

If switchgrass had an EROEI of 1.5, but produced (net, after all fuels and such are accounted for) 2 units of fuel per unit of land, and corn had an EROEI of 1.2, but produced (net, again) 25 units of fuel per unit of land, which is really better? Seems to me that in this (contrived, I know) scenario the corn would be better. Neither of us would have any trouble coming up with complete numbers that would make the above work out (switchggrass uses y units of fuel, and produces z units of mass per acre, etc...)

What is the point of EROEI again? It doesn't seem to be actually measuring anything significant. As near as I can tell, it's measuring the boundaries between the various corporations and occupations that run the system. Seriously, why bother?

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Nate Hagens on August 14, 2006 - 9:45pm

because corporations use boundaries that are too narrow. that is the whole point.

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