EROI and the limits of conventional feasibility assessment—Part 2: Stocks, flows and power return on investment

Update, 24 July 2015: while doing some background work for a forthcoming post that draws on data presented here, I reconsidered the best basis to use for the PV comparison. The post has now been revised to reflect my updated thinking, specifically using a higher EROI for PV of 4.17:1, rather than the original of 2.45:1, by considering only a subset of Prieto and Hall’s energy costs. In the course of making this change, I also discovered an error in the original calculation, in the ratio of emplacement energy to operating & maintenance energy for PV (relatively minor impact only, from 0.59 to 0.55). This is also corrected here.


An important principle to bear in mind for inquiring into the ways that energy-related considerations influence human societies is that, by and large, economies are dependent for their present functioning not on the total stocks of energy sources they might have at their disposal, but on the current rate at which energy sources are supplied and utilised. This is a key distinction in understanding the phenomenon of peak oil. “Peak oil” for a given field or territory is taken to have occurred at the point in time for which the production rate for petroleum—appropriately defined, i.e. by grade or composition—reaches a maximum, and thereafter declines. But at such a time, as much as half of the ultimate resource may still be available. Peak oil doesn’t imply that we’re on the brink of “running out of oil”. What it means is that the production rate is at the highest level that will ever be achieved. It is the change in rate that is central for understanding the implications of the phenomenon for future social prospects, as a declining aggregate oil production rate (i.e. where a shortfall from one region cannot be compensated by increased production from others) implies greatly foreshortened prospects for further growth in the non-energy related economic activity enabled by that production, and in fact very likely implies commensurate economic contraction. The same principle applies to any resource that is ultimately stock-limited, but for which it is the supply rate upon which the present nature of the economic activity enabled by that resource depends. Continue reading