Ethanol from Sunlight

Ethanol from corn


Powering the US
It is argued by advocates of solar energy that ethanol made from corn is useful, if only barely energy-positive.  After all, the distillers use low-grade petroleum fuels to produce high-grade transportation fuel --- ethanol.

On the other hand, it may be wise to look at ethanol production from the standpoint of solar efficiency.  With the data given by Shapouri et al in the reference below ( 2.55 gallons of ethanol per bushel of corn, and then by 122 bushels per acre per year), it is possible to calculate that the land yields a year-round average 789 watts per acre (0.195 watts per square meter), not accounting for the energy input from the low-grade fuel used in distillation and high-grade fuel used in farming and fertilizer manufacture.

When all is accounted for properly, the net yield is a paltry 152 watts per acre, or 0.038 watts per square meter.

We could get all of the energy for the US with a mere 26 million square miles, seven times larger than the US land area of 3.6 million square miles, all devoted to producing ethanol from corn.

Hosein Shapouri, James A. Duffield, and Michael S. Graboski, "Estimating the Net Energy Balance of Corn Ethanol" (paper AER-721):  (RFA=Renewable Fuels Assoc.)

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