Corn Ethanol EROI

Corn ethanol's EROI of approximately 1.3:1 means the energy profit is razor-thin: for every 100 units of energy spent on planting, fertilizing, harvesting, transporting, and fermenting corn, you get back 130. That 30-unit margin is what flows into the fuel supply.

Compare to the sources it displaces: conventional petroleum at 15:1 or better, wind turbines at 20:1 or more. Low EROI means you need a large gross energy throughput to deliver a small net gain, and that throughput carries environmental costs: synthetic fertilizer production (natural-gas-intensive), water consumption, and land use.

Setting up the accounting. The US produces roughly 15 billion gallons of corn ethanol per year, each containing about 76,000 BTU. Total output: roughly 1.1 quadrillion BTU (1.1 quads).

Applying the EROI. At 1.3:1, you must spend about 0.85 quads to produce 1.1 quads. Net energy gain: 0.25 quads.

If the net energy gain is this small, why does the program consume 40% of the corn crop?

Volume is not net energy. The program was not designed around EROI. It was designed around liquid fuel volume, farm income support, and rural political economy. The 40% of the corn crop produces a large volume of gallons, even if the net energy behind those gallons is modest. Volume and net energy are not the same thing, and policy built around volume targets produces very different programs than policy built around energy returns.

Before evaluating any proposed fuel's role in the energy mix, ask what EROI it delivers and whether the policy target is volume, net energy, or something else entirely.

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