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46 comments on A Net Energy Parable Revisited
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46 comments on A Net Energy Parable Revisited
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"In the case of Brazilian Ethanol from cane the energy of humans harvesting the cane is not counted even though each human is required to harvest as much as 8 or more tons a day. http://redgreenandblue.org/2008/07/28/brazilian-ethanol-is-it-more-effic... While the energy to fuel these human machines is minimal due to long hours and low pay it is substantial in terms of the total input to the production of cane ethanol. In the US since we use inorganic machines we count the energy at least to run those machines (and hopefully to manufacture them) so the ERoEI is higher."
The referenced article suggests that sugarcane in Brazil is mostly grown close to the Equator: not true at all.
But you contradict yourself when you say "While the energy to fuel these human machines is minimal" and "it is substantial in terms of the total input to the production of cane ethanol". I don't know whether you have done a comparison between those human machines and the inorganic machines, but it seems to me that the human machine is incredibly efficient. Both in terms of "building" them and in terms of their "utilization". Unless you have some data to support your statement, I am not worried about it.
The social issues of cane cutters are another thing altogether. What would they do if there was no cane to be cut? Will you feed them? And ethanol in Brazil is really mostly a by-product: cane will be cut for sugar anyways.
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.