156 comments on A Net Energy Parable: Why is ERoEI Important?
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- I have a coal mine. It takes 1 joule of oil to pry 100 joules of coal out of the ground. My EROEI is 100, pretty good, huh.
- Now, I make a small coal to liquids plant on site (that takes, say 10 joules of coal to make one joule of oil, and provides all the electricity, steam, heat, and whatever else is needed by the mine). Now my energy input is 0, and my output is 90 joules. This is 90 / 0, which is infinity. I've just increased my EROEI to infinity by making one small adjustment. IN ANY SYSTEM WITH EROEI GREATER THAN UNITY, IT IS ALWAYS POSSIBLE TO ADJUST THIS NUMBER TO BE ANY NUMBER GREATER THAN UNITY!!!!
So, which mine is better? Well, if we have 1 million joules of coal in the ground, then the first one will produce 1 million joules, in exchange for 10,000 joules of input oil. The second one will produce 900,000 joules. It is not clear that the second one (with an infinitely better EROEI) is actually the better situation. The problem is that the only resource of significance here (the coal) wasn't considered at all!!!! What type of a metric is that?!?!?So, using efficiency....
1) If it takes 10 joules of coal to produce 1 joule of oil, then each 100 joules of coal produced is really making a net energy contribution of 90 joules. The efficiency of the mine is therefore 90%, in either case. If the mine can be adjusted so that it runs off of electricity, which only has a 2 to one conversion factor, then the efficiency is 98%. In either case, whether or not the coal is actually converted to this or that is irrelevant. The mine will function with 90 or 98% efficiency, meaning that somewhere between 900,000 and 980,000 joules of energy will be made available by that mine. End of story.
EROEI terms are much more specific than efficency. Your coal to liquids example is incorrect if you put coal in it your input is not zero, if it was fischer tropp (spelling) would be a fountain of energy. The coal is the input. You can heat it with propane or coal or nuke or whatever but using EROEI totals all inputs and calculates the value of end product. Some products are more valuable (diesel vs coal) becuase of their form but that is why we convert them. Every conversion has process losses, that is why engineers always look for ways to capture lost energy. (exhaust heat boilers etc)
matt
If you're including all inputs, then it can never be greater than one, thermodynamics being what it is.
So, why do I keep seeing these EROEI numbers of 5, 10, 1.2, etc. thrown around?
So what you're really saying is this...
- We have a process for converting these "free" input to useful output.
- We consider the utility of this process based on only the amount of non-free inputs it consumes to produce outputs, not on how efficiently it converts the free inputs to useful outputs.
Is that really what you're saying, because that is what EROEI is. And it can be infinite, look at my example above. What exactly is wrong with it?If you have an ethanol operation that runs everything off of ethanol, then energy input is zero (0), whereas "energy returned" is (presumably) something not zero. If energy returned is zero, then it isn't a source of energy, case closed. If it is not zero, then the EROEI is infinite, by definition. How is this a useful number again?
Seems like nomenclature to befuddle the foolish if you ask me. Use efficiency, it has some basis in science, and makes perfect sense. Such as "with what efficiency does this ethanol process turn sunlight into ethanol?". Answer that question (it isn't terribly hard), and you know, for instance, how many acres of land would be needed to produce X units of ethanol. Simple, useful.
That's so irrelevant though. Ok, if you count it that way, then a process that didn't use any fuel (like having peasants harvest it and not using irrigation...) would have a vastly higher EROEI, even though it would be wildly less efficient than just using the ethanol from the output to run the machinery.
How can this be a meaningful number if it's boosted dramatically by disposing of the machines, even as that causes output to plummet.
What exactly are you trying to measure? The efficiency of converting sunlight into fuel? EROEI doesn't even touch on that problem, so what good is it?
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?
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?
1st Law of Thermodynamics:
Energy cannot be consumed or destroyed--only transformed from one form to another. (Energy must be conserved.)
2nd Law of Thermodynamics:
When energy is transformed from one form to another, some of the energy is necessarily transformed into heat. (Entropy always increases).
In a closed system--a system in which no energy can enter or leave--every energy transformation increases entropy and makes less transformable energy available in the system. The earth, however, is an open system--there is a constant flow of energy arriving at earth from somewhere else and a constant flow of energy escaping from the earth.
The fundamental energy source for all life on earth is the sun. Plants (and some bacteria) transform electromagnetic energy (light) into chemical energy. Much of the light energy is lost to heat during this transformation. Living things then transform that energy into other forms to carry out life processes (e.g. organisms move by transforming chemical energy into kinetic energy). If the organism has stored chemical energy and dies before it can be used, that energy can be "harvested" by other organisms. Thus they have found an energy reservoir.
We can sum up the process of energy transformation on earth:
--> indicates an energy transformation
- mass enegery --> heat energy (via thermonuclear fusion in the core of the sun)
- heat energy --> electromagnetic energy (via radiation at the sun's surface)
- electromagnetic energy --> chemical energy (via photosynthesis by organisms on earth)
Energy stored in chemical form can be transformed by humans to do "useful work". Here are some common exosomatic energy transformations that humans initiate (i.e. energy transformed outside our bodies, not used internally):- chemical energy --> heat energy (via oxidation/combustion)
- heat energy --> kinetic energy (via heat engines, e.g. steam or ICE)
- kinetic energy --> electromagnetic energy (via electric generators)
- electromagnetic energy --> heat energy (via your stove, TV, computer, etc.)
In transportation, Step 5 is the human end-use--kinetic energy is the form of energy we desire in order to quickly transport ourselves in cars, airplanes, etc.The conclusion of Step 6 provides energy in the form of electricity.
In every single step described above, energy is lost as heat during the transformation process.
A oil deposit is a reservoir of energy, that is, it is a large reserve of stored chemical energy. All of that stored energy can be obtained and released (transformed) by using a much smaller amount of energy. This is EROEI.
Even so, it is still not a useful number. Imagine I made an oil rig (or whatever...) that ran off of oil (as they actually do). Now EROEI is infinite, as there is no energy input. It takes energy from the reservoir, and uses that to proudce more energy from the reservoir, some of which it sends on too the next stage in the process. Energy input is zero, energy output is not zero, therefore EROEI is infinite.
You say that EROEI (for oil, for instance...) is 2, or 10, or whatever, but this all depends on where you draw the lines. Draw the lines to include the refineryy and all the machinery to drill, pump, and refine the oil, and the EROEI is infinite. Draw the lines around all of Saudia Arabia to see this effect, or do you think they import gasoline to fuel the pumps that pump oil? Saudia Arabia has an infinite EROEI, but so what? This makes absolutely no difference in the real world. A number that has nothing to do with the process, and everything to do with where the lines around the process are drawn is not a viable way to describe the process itself.
It still seems that it's all about what you consider input. If you consider the "free" coal in the ground to be input, then EROEI is always less than one. If you don't, then it can be infinite. Really, it's as simple as that. If you include all inputs, then it's the same as efficiency, if you don't, then it has no meaning. The laws of thermodynamics don't cover something as arbitrary and contrived as EROEI, any more than they tell us how high the stock market can go.
Free inputs (fossil fuels, renewable flows) plus the technology that accesses them plus the efficiency of consuming them.
FREE(stocks +flows)*efficiency of production *efficiency of consumption = societal EROI
I guess I am not following this at all. For this step, if you input 10 joules of coal and got one joule of oil, your energy return on energy invested it 1 joule of oil per 10 joules invested, or 1/10. Nine joules were apparently consumed while making the oil.
To be sure, people apply EROEI in many different ways. This becomes especiallly important in 2-step processes like you describe above. I have seen people calculate 5/1 and 9/1 for exactly the same process, depending on the assumptions.
For instance, let's say I have an oil extraction EROEI of 10/1 and a refining EROEI of 10/1. If you do the calculation correctly, the overall EROEI is 5/1. However, here is how to do it incorrectly and get 9/1. Use 1 BTU to extract 10 BTUs of oil. Now, take 1 of those BTUs of oil, and refine to gasoline and diesel. The apparent EROEI is 9/1. I input 1 BTU, and got 9 back out. But can you see the problem with this scenario? Hint: It is like the difference between simple interest and compounded interest.
In your example, I think that coal in the ground is the "gift", and mined coal is the "useful" energy. Other forms of energy (oil, electricity) are the inputs. But why not use a process in which coal itself is the input?
By doing this, you correctly conclude that the EROEI of the process can reach infinity, and that it may not be a very useful number in this case. But also notice, that by doing so, you have reduced the yield of coal. Less coal per unit time when some of it is used for the process. This seems to indicate an unavoidable trade-off between EROEI and yield.
Nevertheless, EROEI is probably still a useful concept when dealing with renewable energy "gifts" (the solar energy flux), and the inputs are fossil fuels, which need to be minimized for a number of reasons.
For example even the EROEI of ethanol from corn can push towards infinity if some (most) of the ethanol product was used for the input. But the yield per acre would be ridiculously low. With better sources (sugar cane and presumably cellulosic), the yield is probably high enough to use some of the biomass as energy inputs in the conversion process, and still get a decent yield. Having a high EROEI with reduced yield is still probably important if we really want to minimize the fossil fuel input.
Or so I think. Objections?
$RO$I is an accounting nightmare.
It's all a matter of what you choose to count and what you choose not to count or fail to count.
I very much agree that output in the eROeI equation must be qualified as "useful" energy; and I would add to that "in a timely manner".
Due to conservation of energy law (thermodynamics), energy out is always same as energy in (and eROeI always equal to 1) if you allow "energy" to mean ALL energy as accounted for over infinite time. In the oil equation, we blindly discount solar energy accumulated over millions of past years.
Regarding "in a timely manner", I wonder it Hirsch/Bezdek got some of their input from "Beyond Oil" (Gever, Kaufmann, Skoel and Vorosmarty)
Figure 7-1 Comparison of Net energy Production If Society Invests in Fuel-Producing Systems before Fuel Quality Declines versus Investing When Fuel Quality Actually Starts Declining
Green line is production if investment begins before decline, red line is if investment begins during decline. Can you imagine society at 30% of todays energy levels? And that is WITH all current alternative energy technologies.
My conceptual framework recognizes "gift" energy, "useful" energy and the input energy necessary to power the specific conversion process from "gift" into "useful".
A specific process may in fact utilize some of the "useful" energy output as a process energy input. This type of process will increase EROEI at the expense of decreasing yield.
These processes have physical and environmental significance if this substitution reduces the fossil fuel dependence of the process energy.
This is exactly the point. EROEI doesn't matter, only yield, aka efficiency. If I can convert a coal bed to gasoline with 70% efficiency, what do I care if I buy the gasoline from someone else (EROEI of, say, 3) or make it myself (EROEI of infinity). Does that have any physical significance? No, so who cares? Only yield matters. If EROEI is less than one, you will see easily enough that the yield is negative, and hence not a useful source of energy. Even better, by forcing the conversion, it forces a reasonable form of equivalence between the various types of energy.
here's another one that illustrates that point.
- Mine coal using machines using electricity.
- Burn coal to produce electricity.
If you count the coal mine alone, its EROEI might be (for example) 1.5. You'd think that's good, but it's only good because you're taking electricity (very useful energy) as energy in, and producing coal (not very useful) as output. The conversion between them is 2:1, roughly. The coal mine wiht an EROEI of 1.5 doesn't produce enough coal to power itself, if you included the electrical plant in the system you'd see that.Use efficiency (assume that coal is burned to produce the electricity that runs the mine) and you immediately see that the efficiency is negative. There is no output after all the inputs are generated from the output, and the real input (the coal) is most definitely not zero. Efficiency explains it perfectly, EROEI does not.
No, not true. EROEI makes sense ONLY in a situation where the outputs of the system cannot possibly be used to produce the inputs. In that sort of case, then yes, the day we run out of oil, there won't be another drop of ethanol ever, so it does matter.
This is not reality however. Farm machinery could (in theory at least, in reality if the market forces it to...) run off of ethanol. Consequently, it's easy to imagine an ethanol producer with infinite EROEI, as energy input is zero, it is using its own ethanol to produce more ethanol. How is this number useful if a tiny tweak to one stage changes it from 1.2 to infinity? Do you REALLY know what all those tractors burn out there, is that really the point of the research?
Here's another example. Ghawar has an EROEI of 100 (or whatever), but Saudi Arabia has an infinite EROEI, because they don't import energy. EROEI doesn't have any of the properties of a useful number. It doesn't describe the process, and is not additive in any way. A single oil field has an EROEI of 100, but a country full of oil fields has an infinite EROEI because it also contains refineries. Oil field has EROEI of 100, refinery has EROEI of 10, refinery plus oil field has EROEI of infinity, WTF?
It is just not useful. You give me a process, and if its EROEI is greater than 1, I'll make it into any positive number greater than 1 (even infinity) by just adjusting the fuel mix of the various machines used in the process. Why do people argue about a number that is so blatantly fabricated?