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Tuesday, April 12, 2005

Unwise Use of Numbers - Part 2

Randell Jesup provided a good comment to a previous post. A careful reading of a passage shows some ambiguity in what the authors tried to convey. The relevant statement here:
"As you can see, the fossil energy input per unit of ethanol is lower -- 0.74 million Btu fossil energy consumed for each 1 million Btu of ethanol delivered, compared to 1.23 million Btu of fossil energy consumed for each million Btu of gasoline delivered."
I don't believe I misread what the author wrote, but I do think the author totally screwed up in writing what he intended to convey. Note that both the ethanol and gasoline comparisons have an energy "consumed" comparison. It states that 1.23 million Btu of fossil energy is consumed for gasoline delivered. I call B.S. on the authors for classifying consumption of "delivered" gasoline that has not yet been used. Used in this way, this number will never drop below 1.0 and ethanol will look better than gasoline as long as EREOI stays positive for ethanol.

This shows how it pays to stay vigilant on the way people throw around numbers

Secondly, I think Randell also mentioned how the fuel used in ethanol processing needs the extra overhead that the gasoline got stuck with:
0.74 MBTU of fossil energy to produce 1 MBTU of ethanol means that if this is correct, you can draw less oil from the ground, use it to grow whatever and turn it into ethanol and transport it, and be around 0.5 MBTU ahead of petrogas (so far as the draw on the oil/coal reserviors goes) to get 1 MBTU to the pumps. If, instead of fossil fuels, you use ethanol to generate ethanol, you need to produce around 2.5 MBTU total. (That 0.74 MBTU to get 1MBTU of ethanol requires 0.74*0.74 MBTU to produce. That requires likewise, etc.)

Keep calling people on the B.S., me included.

2 Comments:

Professor Anonymous Anonymous said...

Have you links to other opinions who expose this mis representation as it seems to be remarkable successful in infiltrating the web...

I have only seen two people refute this presentation thats you and me!

Boris
London

(mididoctors at peakoil.com)

8:17 AM  
Professor Blogger WHT said...

Pimental from Cornell has done a bit of criticism (putting it mildly).

9:39 PM  

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