See the response to my post below.

http://www.theoildrum.com/node/3810#comment-328100

I don't know if my numbers are right or not. But using my weird methods I also came up with 5:1 as probably the real lower bound EROI. This is mentioned in the key post.

Also in my post I think our current EROI is actually 10:1 not 20:1 my justification is simple. We where at 20:1 about 2002 and prices have increased five fold so that suggests a real EROI of 20/4 == 5:1 right now. Taking into account growth etc 10:1 makes more sense as a high estimate.

If you somewhat agree with that argument then EROI has dropped by 50% in five years with steady oil production. It makes sense that real EROI will probably drop faster once production begins to decline so instead of being at 5:1 if we are not there now in five years we probably will be less.

Of course we are not going to make the massive investments needed to keep net energy levels up so the net energy levels should be and probably are already dropping probably in line with the EROI drop. This would mean that say if EROI goes from 10:1 to 5:1 and absolute production drops by 50% then net return would be say 25% or a 75% drop.

My gut feeling has always been that if we where going to make a smooth transition from oil to alternative energy we would have had to start in the 1970's. Even if my numbers are off I don't think they are off by orders of magnitude. So I simply don't think its possible to make a smooth transition.

Considering we need to invest a significant amount of excess energy into alternatives to speed the transition say 10-25% of todays excess. You can see that when we reach the point of having only 25% of todays excess energy the rate we could make the change drops dramatically. Also of course as current energy extraction process begin to take up more and more of our economic activity they are in direct competition with alternatives. Both are chasing the same shrinking pie. I'd hazard that current approaches would generally win.

Now I'm not saying we can't make such a transition just that from what I can tell it would already be extremely painful if we made it a top priority right now and it becomes increasingly more painful as we wait. And probably worse it seems the time it takes to deploy the amount of alternatives to bring us back to our current free energy levels quickly stretches out to centuries as the ability to expand alternative energy sources contracts to a small percentage of a lot lower net energy level.

Finally as far as our current infrastructure goes very little of it is terribly useful for building out alternatives. Roads and oil based transport are not all that useful over the longer term. Rail would be but in many places it would itself need to be built out. The highway infrastructure in the US is actually in horrible shape and close to collapse and our secondary roads basically need to be rebuilt completely every 10-20 years. We have been abusing this oil investment for a very long time. Given the huge amount of deferred maintenance in roads at best they offer no total support at worst they are and additional place we must invest to simply get our rail expanded. Cars/Trucks etc also have limited lifespans generally less than 20 years again its dubious how much of this can be treated as a stable investment and how much of it would be lost in even 20 years.

Overall after all the money we have spent in my opinion our current infrastructure is only useful for about 20 years of support for investment into alternatives at best. After that we have to have new rail infrastructure in plain to continue development.

In any case pain or not we need to start transitioning off oil yesterday. If we wait to long considering the way EROI seems to work only a tiny fraction of todays population will be able to create high tech sustainable lifestyles and the rate they can expand will be painfully slow.

I happen to think we will end up with these islands of technology in a sea of misery but I'm not the most optimistic guy on the planet.

Ok, now I see what you are doing. The energy needed to refine silicon (say) does not change. But the energy to create the energy to refine the silicon goes up. And this should work for all materials.

What is the damage to society from this change? Hmmm. First pass, I would try to bound the problem to see how much trouble it could cause. So take an extreme example and push the drop from 100:1 to 10:1.

So suppose I have a 100:1 energy source powering my society. I calculate the EROI of some alternative source and it comes out 10:1 (Estimate A). My wonderful power source now declines to 10:1. What will the EROI of my alternative power source decline to? (Estimate B).

Here is my approximation. I am going to change the coding slightly to make it clearer (I would appreciate others to check the math). Society starts with a 100:1 power source that declines to 100:10 (recoded 10:1).

We want to know the impact on another EROI calculation that also has a 100:10 ratio. Ok. Estimate A would include a tiny 1% hidden cost that is the energy cost to get the power which = 10*0.01= .1 units energy. For Estimate B that would increase by 10 times. 10*0.1 = 1

So for Estimate B our alternative energy source would really end up being 100:11. That is not much change. But dropping below 10 would start to get painful. It should be possible to calculate directly this way, and put in a corrective factor. Anyone have a different view?

We can't just input the new intensity of coal and oil because that highway infrastructure will last for many years--how, and over what period do we amortize the energy for that replacement?

I wonder if this isn't addressed better as a time component of Net Energy. We need a "velocity" of energy as it moves through our economy. Energy that has become embedded in long life items is still flowing through the economy, just slower than fuels. An Embodied Net Energy concept.

Brad F noted that there are some miscalculations (or typos) in the table. The number without salt storage should be 34 not 44.

These values for silicon PV should be useful:
http://www.nrel.gov/pv/thin_film/docs/lce2006.pdf

Chris