Re which see my below about more useful concept of
EG/EI (Energy Gain(loss)/Energy Invested).

Are we talking about thermodynamics or economics? I see ER/EI as thermodynamic.

Sheesh, you guys throw out all these high falutin terms and concepts like thermodynamics and stuff... I mean, next thing you know ya'll will be expectin us common folk to be able to understand the Krebs Cycle or sumthin.

Seriously though I wonder how many people of even college level literacy have any understanding of thermodynamics and are able to grasp why classical economic theory is pure bunk.

It seems obvious that there are two quantities here, and making sure they are obvious and separate is a sensible idea.

First there is EROEI talking in simplistic terms about energy and efficiency of extraction. Second there is ROI talking in simplistic terms about money. Now EROEI informs ROI, but so does location, market prices, shade of sky colour in your part of the world, etc.

EROI, energy returned on investment, is a bit of a muddle in the middle, conflating energy with finance. It doesn't really tell you anything and confuses the issue by being too close to ROI in the minds of economists. Don't confuse the poor dears.

Load up your spellchecker with EROI => EROEI and get rid of it from articles unless the author is really incorporating energy with finance. If they are, don't let them get away with the woolly thinking that so exemplifies economists and accounting - they need to define inclusions, exclusions and assumptions.

PS Plastics and fertilisers is a red herring on EROEI. What is output from the resource recovery process is potential energy. What you use it for is another question. Plastics, fertilisers, etc. have high 'energy' inputs because they can use feedstocks that could be energy.

can EROI be negative? ROI can be, ER/EI can't be

ER/EI never negative? On a strict thermodynamic basis this must be true, for energy can neither be created nor destroyed, thus each term must always be positive. (Unless they manage to harness Dark Energy, that is.)

But, to be practical, we are talking about useful energy here, so there is a subjective judgement in what precisely constitutes energy.

For instance, say I use a motorised winch to hoist a heavy weight. Neglecting friction, I have an EROEI of one because the potential energy gained is equal to the work done.

If the rope breaks and the weight falls and smashes my winch, I've ended up with net negative energy, because I've gained zero useful energy from burning my fuel, plus I've lost the energy used to make the winch.

Thus I can get negative EROEI in a catastrophe.

(I realise I have cheated in re-drawing the boundaries of the problem between start and finish, but I am prepared to argue that this is acceptable in a practical situation.)

How about Quanta? Si, muchacho, Planck's constant times its frequency equals more energy for you mi amigo.
Que? quanto custa. No way, Jose...

Energy return on Energy invested or EROEI has huge implications beyond just its thermodynamic properties.

It also suggests that the economic models we use for extraction are wrong since they don't include declining EROEI.

Even though my original energy costs are low and thus generally investment cost if EROEI increases in time this means
you need a fairly significant sort of reverse deprecation to correctly price the "cheaper" original investment.

Thus the oil we extracted in the 1980's had far higher intrinsic worth then we assigned it since we did not back date peak
oil "appreciation" into the equation.

A interesting approach to balancing this is to force any use of a depleting resource to be balanced with retaining a renewable resource.

For example say every thousand barrels of oil equals 1 acre of prime forest or farmland thats left fallow for 20 years. Thus the energy used
in burning oil and even the C02 is banked via setting aside a renewable resource for later use. You could also match to PV and wind etc.

Slightly harder than conserving but same result. As you can see by balancing this way it seems that we do a really good job of ensuring continuous energy and thus we have balanced the EROEI equation. And its a easy way to correctly price oil to include EROEI increasing.

Also it seems obvious by burning oil for a century without attempting to balance has left us in dire straits.

And yes for the most part this means we probably have sold oil at ridiculously cheap prices for some time.

It seems clear to me that attempting to balance the equation when oil itself "costs" the same as renewable using
our normal economic constraints is wrong. Using my approach to make up for the deficit we would have to price oil
at say its projected price in 20-30 years. My best guess would be 500 dollars a barrel.

This makes intuitive sense since if we correctly repriced oil to 500 then we would see a huge burst in renewable energy
development. This would be funded by the difference in EROEI / investment in oil today vs what it would be in 30 years.

Assuming my logic is sound this gives you some idea of what we would really have to do to handle oil depletion correctly.
If we had done it right over the last 100 years then we would not be faced with this huge tax right now and we would
have a stable society. Either we pay the tax or we dramatically reduce our societies energy usage and probably complexity.

EROEI is intrinsic in making it clear that you cannot get out of this situation.