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Comment by benp84 | Hacker News Reader

I was under the impression that corn ethanol was effectively solar energy because corn turns sunlight and carbon into biomass then we burn the biomass back to atmospheric carbon. Isn't that the fundamentals? Is there a big, basic reason it doesn't work or is it lots of little side effects? Thanks for weighing in.

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One other big, basic reason from early school Biology you are missing is the Nitrogen Cycle. Earth crops are not particularly efficient at fixating Carbon into biomass and generally need plenty of other mineral inputs such as potassium and phosphorous and zinc and especially Nitrogen. Nitrogen alone is an interesting problematic "inefficiency" because Nitrogen wants to be a gas at Earth pressures/temperatures (like Carbon) and so also needs to be fixated and plants very rarely have evolved that sort of fixation directly, instead relying on "the Nitrogen Cycle" to (eventually) fixate it into soils.

One of the things humanity has done as it has industrialized agriculture (to deal with the time issue of that "eventually") is that it has industrialized "the Nitrogen Cycle" as much as it can, and in so doing added a lot of additional Carbon inefficiencies to how we fixate Nitrogen for use by our crops. Modern crops couldn't grow at the same industrial scales without modern fertilizers, but modern fertilizers generally don't exist without massive carbon subsidies.

https://en.wikipedia.org/wiki/Nitrogen_cycle

The fundamental reason is producing ethanol from corn requires quite a lot of energy; for cooking the mash and distilling the final product. If the cycle was entirely ethanol "all the way down" it could be carbon nuetral although using ethanol for production would detract from the "total efficiency". Invariably other fuels are used in production.

I went through the math a few years ago from the perspective of "micro power plants" for powering BTC mining. Coal is the winner from a cost perspective; but terribly dirty obviously. And capital intensive. Burning corn as fuel to a high efficiency boiler is actually more efficient than ethanol.

Put simply, the land is fertilized with petrochemical fertilizers that come from oil and have a heavy carbon Footprint, the automated equipment that harvests it and moves it to the processor burns a lot of diesel. It's not as if the corn just springs up, there are costs.

The logic is sound, biofuels can even theoretically reach negative carbon emissions by burying husks and similar.

Corn is just not the best plant for the purpose. Soy or hemp are two better examples, especially for biodiesel.

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