You are correct in one sense that eroei only becomes an issue as the net energy (see clifman's analysis) approaches 1 or zero. Then the externalities of the effort (labor devoted to energy acquisition 'stolen' from other social goods, negative environmental damage,et) become very important issues.

... which is an assumption without real study. If the energy used would be more mechanized and without human input (a perfect machine that would function without human intervention for centuries, for example - and yes, I know it sounds like sci-fi, but we are getting into that), it wouldn't really mean a thing if the EROEI was 1.3. It would only be of importance if the energy output was not enough for our needs. Machines would be restless.

Of course, I'm not endorsing it. The problem with EROEI = 1.3 or smth like it is that it is more risky. If the production line explodes, or major malfunctions, or whatever, you may easily get EROEI < 1. And that's very bad.

This is a problem with biofuels. A major one.

But not with solar and wind and the likes, which have EROEIS in the order of 6-20.

Thing is, there's no other stuff that so easily substitutes oil as biofuels do. That's why such a bad investment is being done. We should question though its wide implications. Ecological, social, etc.

Thanks for sharing your insight; much appreciated. In the words of Stephen Leacock, my thoughts often go "madly off in all directions", but one more tangential question, if I may. Is any credit given to the recovery of energy inputs at the end of a product's service life, assuming some or all of the hardware can be recycled or reused? In the case of a solar panel, say, I take it the aluminium frame can be salvaged and perhaps some of the other components as well, in which case, at least some of the embodied energy is recoverable. On the other hand, I'm assuming much of the concrete and steel used in the construction of a hydroelectric dam or nuclear reactor cannot. Do these types of calculations normally take into consideration residual value when comparing one option to another?

Cheers,
Paul

I think that you want 0.66xGJ for EROEI 2:1. For EROEI 1:1 it is still 0.5xGJ. I think the way you want to look at this is the way you put it terms of scale of the operation. So, start by asking how much energy you want, then pick some quantity like land surface area that has a definite limit, and ask what EROEI is feasable to produce the amount of energy you want from the resource available. That way you know what your minimum target EROEI is. You'll have to put in other details like raw productivity or, for oil, the amount of surface area that has oil under it. In terms of raw productivity, you can accept a lower EROEI for higher productivity since you need less land all other things being equal.

So, lets take, for example, 35 billion gallons of ethanol per year by 2017 set by the president. The raw productivity is about 400 gallons/acre/year for corn so we need about 86 million acres or 137,000 sq mi or 2.4 Iowas. You can do this with any EROEI that you like, but if you want be sure that you get the whole 35 billion gallons for use other than say growing corn, you need to give a limit on how much land you are willing to devote, say 4 Iowas, and look for a target EROEI that lets you do this. In this case you would be using 1.6 Iowas to support net energy production from 4 Iowas so your target EROEI is 2.5. Now you have said something helpful. You are not going to use more than 2.4 Iowas to meet your production target but you know where the self-sustaining EROEI is. Then you are fine using natural gas and oil to grow corn because you are not putting a greater burden on those resources that is not compensated for elsewhere by the ethanol. As it turns out, getting to an EROEI of 2.5 does not appear to be feasable using natural gas and oil, so you need to think of something else. One thing you might do is ask how many Nevadas it would take to produce nitrogen fertilizer using solar power and a low pressure aluminum nitride process instead of Haber-Bosch because then you effectively increase the usable land area to non-arable land. If you innovate in various way, you might get to the target EROEI. The usefulness of EROEI is to be able to ask and answer what if questions of this type.

Chris