4 replies to this topic

[eaglecreek]

what's the difference between net energy yield and eroi?

[Shortpoet-GTD]

eaglecreek, on 11 July 2012 - 11:16 AM, said:

what's the difference between net energy yield and eroi?

It would be better if you explained what eroi is to those that don't know. (We can google it, but you asked, so why
should we have to look it up?)

[eaglecreek]

"energy return on investment" for those that dont know.

[QuatreHiead]

My guess just from the words is that the net energy is just an overall value of how much energy output, whereas the EROI is a relative measurement based on the investment or work put in. In which case EROI puts the net energy value into perspective to give perhaps a more realistic picture of how well and efficent the product is.

I hope this is helpful. Someone correct me if I am wrong in getting the idea behind the terms.

[still learning]

eaglecreek, on 11 July 2012 - 11:16 AM, said:

what's the difference between net energy yield and eroi?

As I understand them....

Net energy yield: In a process like the production of fuel ethanol from a crop, a determination how much useful energy is "gained" in the process.
Literally, there won't be a true net energy gain since energy is conserved, no actual net change as long as only non-nuclear processes are considered.
Usually in determining net energy yield only the kinds of energy that actually have some commercial value are considered how much the net gain or loss is.  In the fuel ethanol example ordinarily the energy from sunlight used by the growing corn isn't included in the accounting.  Some of the things that would be included in a corn ethanol accounting would be the fuel used in plowing and planting and harvesting  and transporting the corn, add the energy of the electricity used to run the pumps and whatnot in the corn fermentation process, add the fuel needed to distil the ethanol.  Making the necessary conversions (joules, watt-hours, BTU's, etc), add up all the useful energy used in the ethanol production process and subtract it from the amount of energy that can be recovered when the ethanol is burned as fuel.  If the number is positive, then you've gained.  

for eroi (or somettimes eroei, make much the same accounting but divide the output energy of the process (the ethanol) by the input energy (the fuel and electricity used)

So, the difference between the two is that net yield is a number with some kind of energy unit attached, such as 27 million BTU's while EROI is just a number such as 7.2 that doesn't have units (divide BTU's by BTUS and the units of measure cancel)

Note that time isn't included.  

What wikipedia says:
net energy gained http://en.wikipedia....Net_energy_gain
eroei  http://en.wikipedia.org/wiki/EROEI