OPEN SOURCE, PUBLISH FREELY Anonymous
But I hope I can answer your question. At ERoEI = 1 there is no net energy and by definition everyone is working in the energy industries making the cost of energy hugely expensive. This of course cannot happen. But at ERoEI = 2 then perhaps 50% of the population are engaged in energy industries and 50% of the energy produced gets used to get more energy not leaving much net energy (or people) to work in manufacturing, schools hospitals etc. To have same net energy that we have available today the amount of gross energy being produced may have to double from where we are at present and it would be prohibitively expensive.
But recently I have received this via email from Nate:
There’s an interesting story there. For years bloggers have maintained 5-7 citing Charles Hall. But when I asked him for the reference he said he’d never published that. But he may have mentioned it to someone over a beer. He currently says ERoEI of at least 7 for society to function.
But then there is a contradictio in terminis, because hunter gatherers were not known for building up complex clean chambers with their micrometer air filters or sophisticated machines to cut in fractions of millimeters the ingots to produce the wafers, robotic soldering machines with micrometric precision to make the silver connections between cells, or electronic factories to produce the solid state power devices like the IGBT’s of the inverters.
Figure 3 The estimated energy content of common materials 
Sumerians were the first ones in being able to release kings, priests and military from productive works with the net energy surplus left once we pass to the Neolithic, domesticated animals and plants and stored them in the form of available energy surplus.
The post was much improved by comments provided by Prof Charles Hall.
Being the minimum EROIext for any live being (mammals in particular) 2-3:1 in average, to be kept alive as species and for the couple to successfully breed their offspring (minimum of 2-3 per couple), probably Charles Hall is very right to state that a minimum EROI of 5:1 is required to have a minimum (very primitive and elemental) of civilization, beyond us living as naked apes.
Energy Costs of Energy Savings in Buildings: A Review
If we pick the latest Sankey Diagram of the International Energy Agency (IEA), and take in one side the 13,137 MToe/year (or 17 TW of equiv. power) of primary energy and what the IEA calls “own use” (self consumption), which is 784 MToe/year, we get a rough global energy EROI of about 16:1. Should we use it the final energy values after losses (8,917 MToe/year), then we get roughly a 10:1 EROI and this is extended.
Euan did you get a chance to read paper quoted by David Mackay
Very easy, Roger. Look first to the picture of the cheetah in the article of Euan on EROI for beginners. That beautiful and ultra efficient machine, needs an EROI of about 3:1 (sped three times less energy running for the prey, that the energy contained in the prey it is going to eat. That’s a metabolic minimum EROI for mammals.
Its a dangerous business to become reliant on government subsidies.
If you want to feed your wife and 2 children aren’t we up to 3 or 4 already, if they are lazy? A society that includes footballers, mime artists, beauty therapists and solar panel manufacturers, and in which granny is not to be left out as lion food surely needs 5 to 7 at least!
But keep at it with KiteGen. Sounds as clean as it gets.
Not even growth, I think. The human body emits about 100W give or take, so an ERoEI of 1 equates to sitting in a fruit tree and just eating 100Wh of fruit per hour. Equally, if you run around catching rabbits or whatever then you’d better make sure you catch enough of them to keep your weight up!