"Dave Hinz" wrote in message
...
On Sun, 16 Sep 2007 19:07:58 -0400, ATP*
wrote:

"Dave Hinz" wrote in message
...

You'll be providn' a cite for that claim, right?

http://www.news.cornell.edu/stories/...ostly.ssl.html

Ahhh, Pimentel.

Interesting thing about Pimentel. In 1994, he co-authored a paper which
stated "Solar energy technologies, paired with energy conservation, have
the potential to meet a large portion of future US energy needs".
http://dieoff.org/page84.htm

Not sure that that's feasable. Later on, the paper says:

"Ethanol. A wide variety of starch and sugar crops, food processing
wastes, and woody materials (Lynd et al. 1991) have been evaluated as
raw materials for ethanol production. In the United States, corn appears
to be the most feasible biomass feedstock in terms of availability and
technology (Pimentel 1991)."

In this very paper, is the nugget of his that keeps getting thrown
around, 16 years later, as if it's current: "The total fossil energy
expended to produce 1 liter of ethanol from corn is 10,200 kcal, but
note that 1 liter of ethanol has an energy value of only 5130 kcal.
Thus, there is an energy imbalance causing a net energy loss.
Approximately 53% of the total cost (55¢ per liter) of producing ethanol
in a large, modern plant is for the corn raw material (Pimentel 1991)."

Yet, further in the paper, they write:
"The most promising systems rely on distillation to bring the ethanol
concentration up to 90%, and selective-membrane processes are used to
further raise the ethanol concentration to 99.5% (Maeda and Kai 1991).
The energy input for this upgrading is approximately 1280 kcal/liter. In
laboratory tests, the total input for producing a liter of ethanol can
potentially be reduced from 10,200 to 6200 kcal by using membranes, but
even then the energy balance remains negative."

So even Pimentel knows, for at least 13 years, that with 13 year old
technology, it took 6200 kcal of energy input to produce the 5130 kcal
worth of ethanol. So his very own figures show an 82.7 percent
efficiency, with 13 year old technology. Also, these figures ignore
possible cogeneration or other uses of "waste" heat, and of the material
left after the fermentation. Brewery byproducts used as cattle feed,
for instance.

Now, if we'd power the ethanol plants with nuclear-generated
electricity, then even the 17% net energy loss that existed 13 years
ago, is a lot more attractive than what we're doing now.


Pimentel updated his data in 2005 and he still shows a 30% net loss.

The argument has boiled down to a question of how far you go with an energy
audit. Pimentel says you have to go all the way through the machinery costs,
the machines-to-make-the-machinery costs, and so on. His detractors, such as
Bruce Dale of Mich. State, say that violates academic standards for
scholarship on such issues.

But does it? When you close the system under consideration, as we can almost
do with petroleum, all of these arguments disappear when we measure how much
gasoline is produced, and then measure how much is purchased by consumers.
The difference is the loss, which is considerable.

When you're using petroleum and gas sources to produce ethanol, you get into
the argument over what is really a production cost (energy, as well as
dollars). The only sure way to know the answer is to close the system, so
that all of the energy costs needed to produce ethanol are fueled
by...ethanol.

If you can't do it, I think the logic is in Pimentel's favor: a great deal
of energy costs to produce ethanol get lost or passed over because petroleum
is fueling the entire support and production system, and the systems that
produce those systems, and so on ad infinitum. Take away the petroleum and
the whole thing, says Pimentel, collapses.

The DOE, academicians like Dale, and most particularly the interested
parties such as ADM and farm-state politicians gloss this over or try to
dismiss it, as Dale has tried to do with Pimentel. I find Pimentel's logic
more compelling. And with his more recent data, I think the argument over
his basic numbers goes away, too.

--
Ed Huntress