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2 July, 2005
I was recently informed by a fuel ethanol enthusiast that
the EROEI (Energy Returned On Energy Invested) of ethanol
from agricultural products had been greatly increased from
1.38 to 2 He was incredulous, to say the least, when I
told him that was not nearly high enough for ethanol to
serve as a primary energy source that could keep
business-as-usual going after the oil peak. Actually, he
accused me of being a supporter of the oil industry,
anti-farmer, and a despoiler of the environment, and would
not listen (shouted me down in fact) when I tried to explain
the realities to him. So, to restore my equilibrium, I am
now imposing on you what he refused to listen to.
I show below that ethanol cannot replace the fuel shortages
that peak oil will bring, at least not without a very large
increase in the total amount of energy we produce. This will
be a problem, to say the least, when the energy available
from oil and natural gas is declining.
The deficiency of ethanol is its low energy profit ratio.
To make the notion of energy profit ratio a little more
precise, consider the following definition of EROEI, or Energy
Returned On Energy Invested. (I like to pronounce it
ee-ro--ee.)
The EROIE of a primary energy technology is
the ratio of Energy Returned to Energy invested.
Energy Returned is the amount of energy that an energy
producing technology produces for all uses, including
further energy production.
Energy Invested is the amount of energy already available
for use by society that must be used by the energy
producing technology to produce the Energy Returned.
Note that the Energy Invested is not the same as the sum of
the energy inputs to the process of operating the energy
producing technology. Energy Invested is only that part of the input
energy that is already in a form in which it is ready for
consumption in society--gasoline, ethanol, diesel fuel, coal
ready to burn, etc, but not crude oil,
sunlight, wind energy, etc.
Also note that an EOREI = 1 is the break-even EROEI. Unless
a primary energy technology has an EROEI greater than 1, it
is obviously useless. A fuels technology might be useful in
special circumstances at an EROEI less than one, but it
would take more energy from some other source to produce the
fuel than the fuel delivered in use.
Let's take the EROEI of the energy derived from the
oil industry in the US as a comparison. Robert Kaufman,
http://www.bu.edu/cees/people/faculty/kaufmann/index.html
calculates it as about 10 for extraction in the US in 2000.
Because the US is a very mature oil province, this is
probably low for the world as a whole. The value 10
is read from image 33 in his talk at Lawrence Livermore Labs,
"Oil and the American Way of Life: Don't Ask Don't Tell",
http://vmsstreamer1.fnal.gov/VMS_Site_03/Lectures/Colloquium/050601Kaufmann/index.htm
(An outstanding talk, by the way.)
So, lets compare two transportation fuel producing
technologies, ethanol with an EROEI=2, and diesel, gasoline,
JP4, etc. with an EREOI=10. The relevant question is how
much energy does society have to produce in total to get the
same amount of energy for transportation use from each technology?
Petroleum's EROEI = 10 means that for each ten energy-units
of oil-derived fuels you produce you get to keep 9 energy
units for uses other than fuel production, since you have to
put aside 1 energy-unit to produce the next ten units.
Ethanol's EROEI = 2 means that for every 2 energy units of
ethanol you produce, you get to keep only 1 energy-unit for
uses other than fuel production since you have to put 1
energy-unit aside to produce the next 2 energy-units.
Therefore, to produce 9 energy-units of ethanol fuel for uses
other than fuel production you have to produce 9 additional
energy units for use in fuel production, for a total of 18
energy units of total energy production for fuels.
To restate in a general form that does not imply the
invested energy is necessarily from the energy technology
it's invested in: For 9 fuel energy units for uses other
than fuel production you have to produce a total of 10
energy units if the 9 fuel energy units are from oil, and 18
energy units if the 9 fuel energy units are from ethanol.
In other words ethanol fuels require a 1.8 times the total
energy production for a given fuel-energy for uses other
than fuel production compared to petroleum fuels.
Therefore, to replace a given amount, FE, of oil derived fuel energy
by ethanol fuel energy, thus keeping the available fuel energy
constant would require *increasing* total energy production
devoted to fuels by ((18/9) - (10/9)) x FE = 0.89 x FE.
Consider a policy of keeping the energy available from oil +
ethanol fuels for uses other than fuel production constant
by replacing the fuels derived from oil as oil production
declines at 2% per year after the peak of oil production.
This constant fuel energy replacement policy would require
the total energy for fuels produced by society to rise by
0.89 x 2%= 1.78% per year--a doubling time of 39 years.
This additional energy would have to come from renewables,
coal, nuclear, perhaps even still more ethanol. It is a
gigantic amount. World oil production will decline at a
fairly constant rate of 0.5 billion barrels per year for
40 years (ASPO). This is approximately 100 gigawatts per
year per year. If we assume that 2/3 of this is used as
fuel, we would require an increase of total energy
production of 0.89 * 2/3 * 100 = 59 gigawatts per year per
year just to keep the worlds fuel energy from oil + ethanol
flat. This is the energy production of, for example, 59 big
nukes or big coal generating plants. That's equal to the
additional
energy produced by 59 *new* big nukes or new coal plants each
year--just to keep the fuel energy from oil + ethanol constant.
To *increase* the transportation fuel energy from oil +
ethanol by E% per year by ethanol production would require
an *additional* 2 x E% increase in the total-energy
production devoted to fuels. So the total increase per year
in total energy production for fuels would be 1.78% per year
to offset the 2% decline of oil production plus another 2 x
E % per year for the E% increase.
In other words, after the oil peak, a 1% per year increase in oil
+
ethanol transportation energy would require 3.78% increase
per year in total energy production for fuels--a doubling
time of 18 years--a 2% per year increase in oil + ethanol
transportation fuel energy would require a 5.78 % increase
per year in total energy production for fuels--a doubling time of 12
years.
Good-bye business-as-usual. Or good-bye biosphere. Or both.
David Delaney
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