In a message dated 8/8/00 1:34:31 PM, firstname.lastname@example.org writes:
The yield of the process is 100%: you need a lot of energy to make
the ethanol but the energy consumed needn't have been from ethanol.
So the yield is 2.9E16 BTU, with a requirement for 1.7E16 input.
However, we could probably do better. From the site you reference,
>>Cellulose to ethanol is currently too expensive to compete
>>with corn as a feed stock but new technologies might make
>>it a commercial reality within the next decade. Newly developed
>>enzymes are being researched that will convert cellulose to
>>sugars which can then be fermented into ethanol This would
>>mean not only having a greater supply of clean burning,
>>renewable ethanol but would also reduce the volume of waste entering our
Plants produce a lot of cellulose, so yields could be far higher than
for corn *if* we pay more for the ethanol (the site doesn't say
*how* much more) or if we develop cost-effective fermentation.
That said, we'd still need an awful lot of land.
>Corn yield/acre about 150 bushels / acre:
>Ethanol yield about 2.5 gal / bushel:
>Energy consumed in corn production & ethanol production:
>So net yield is 42% of gross yield, so
>Net yield 150 * 2.5 * .42 = 157 gal / acre
>Total US Farm land in 1990 from Almanac: 988,000,000 acres
>Ethanol 7.6E4 BTU / gal
>Imagine all US farmland in corn, 1.6E2 * 9.9E8 * 7.6E4 = 1.2E16 BTU
>Total US petroleum products consumption in 1989: 3.4E16 BTU.
>So if all the proles now growing anything grew corn instead, and we
>it and burned it in our detroits, we would displace about a third of
>the oil currently being used.
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