Notes while trying to wrap my head around the discussion held at https://www.researchgate.net/post/Why_is_quality_of_life_limited_by_EROI_with_renewable_Energy.
The discussion there revolves around, and my initial calculations indeed were, as James E. Miller presents them, that you input an initial 1 unit of enery, and with a PV or 3:1 EROI, you take 1 for society, and 1 for investing in another PV, and stack that way. This reasoning does seem to imply that you can stack them, but ignores the fact that a society of comparable complexity (a prerequisite to being able to build PVs in the first place) to ours (so every person in society) needs an EROI of 15-10:1
So, if you scale the example down to a few PVs, you also have to scale the whole machinery we have for PV production down. For that to work, everybody needs an EROI of lets say 10:1, and all those people are all assumed to work ~8 hours per day at current well-being levels. If you need more people to do the job, PVs become more expensive (or require more energy for automatization), and your EROI goes down (you need to invest more money to get one, which you earned spending energy/time).
So, yes, if people wouldn't starve while making PVs, stacking would work, but you first need to reach a baseline of EROI 10:1 for everything in your society to remain working before you can even think to use excess energy for stacking. E.g. you need 10:1 to keep your head above water, otherwise your society well-being will go down (the claim being made, level of EROI needed for sustained level of well-being).
If while you're stacking PV energy, people are starving, it obviously won't work, and also the whole excersice becomes sort of pointless.
The energy to fill the 10:1 can't from anywhere else, because in a carbon-neutral society there isn't anything else! If you do have part of your economy working with fossil fuels to make this excersise of stacking work, then the fossil fuels are subsidizing the production of PVs (as they do today), and you're not carbon neutral.
So it's a bit like saying if we lived in caves and food would fall into our mouths, clothes would fall in our laps, a PV factory would build itself? (e.g. no effort required to get to a level where we can show up for work? at the PV factory?), we could stack PV power like this. You can start to see how the boundaries of the calculation become important, as C. Hall mentions.
We need energy for (survival) + (level of well-being) + (infrastructure) to make PVs.
So.. trying to concluse... only the energy level in excess of your society needs can be considered as energy free to use for stacking, so you need renewables to be of an EROI of 11-12-13:1 to start thinking about stacking them. Which is just not the case for renewables.
On the other hand, in current society, we also only need 10:1, and the extraction cost for fossil fuels is supposed to be included in that, but the fraction of 10:1 for an energy source of 30:1 is going to be a lot smaller in absolute quantity, so will be a lesser part of your economy.
So (30:1 EROI for fossil fuels)/(3:1 EROI for renewables), energy would require a 10-fold (1000%) bigger part of your economy to fulfill it's perpetuation? All the people now involved in working in PV were previously doing other useful stuff, that they now can't do. This is why it won't work?