Human muscles are about 16% - 20% efficient, according to Vaclav Smil, Energy in Nature and Society (2008), Chapter 5. So, nearly comparable to gasoline engines, or a bit less efficient than diesels.

Of course, with non-working time, and the energy inputs into growing and transporting the workers' food, the final net efficiency would be lower. And if the workers are eating meat, lower still.

William when I said the energy of using humnan Brazilian is minimal I mean that in the sense that the energy "paid" to these workers is pretty much just the minimum needed to keep them alive (briefly) and working. Basically enough energy for food and a tad of shelter. The energy US humans require for their work is vastly larger. They require energy for food shipped from all over the world with a heavy meat component, energy for building and driving a car, building and heating/cooling a large house etc. In Brazil since you can get away with paying humans the minimum energy credits to survive for a few decades using humans is more cost effective than using machines. In the US even using illegal aliens many farm tasks are more cost effective using machines. Money in the end is energy credits and roughly corresponds to energy inputs.

I wasn't addressing the social issues, just how do you count ERoEI. If you don't count at least the energy necessary to keep humans alive to do whatever work they do in the process you haven't counted all the energy. My main point was that if in the case of Brazil you don't count at least the energy needed to feed the humans while in the US you count the energy needed to harvest the corn by mechanical machine then you don't have a genuine comparison.

Supposing you think of it this way, if in a US solar panel factory they were using their own solar panels to power the factory and instead of using money they used more solar panels to pay their workers with electricity, that extra electricity they had to generate would be part of the energy input for making more solar panels. But because they give them a paycheck the energy credits embodied in that paycheck are not counted.

This will become more clear to everyone as cheap energy runs out. Regardless of how efficient we are compared to mechanical machines we are machines that require fuel and if you don't count that energy you haven't counted all the energy inputs.

Pitt can you substantiate that statement. What are the caloric needs of a human cutting 8 tons of cane a day. You also have to count the calories to feed the family just as a hunter gather has to kill enough prey to feed his family. Housing and transportation are energy needs of that human too, as well as medical care. In a complete system you also have to count the calories needed to raise that child from an infant...some figure apportioned out over the years of their life.