Is ethanol efficient?

“I heard that the energy it takes to grow and produce ethanol (gasoline for tractors, process to make ethanol, etc) makes the whole thing a farce”

“What is the net energy balance for ethanol?”

“I read that the energy return on energy invested is negative for ethanol, is that true?”

We get this question fairly often.

First off, the energy balance question is nonsensical – it always takes more primary energy to produce a unit of usable energy – that’s just a basic law of nature – whether the primary energy is a lump of coal, crude oil, or corn and the usable energy is electricity, gasoline, or ethanol respectively. The right question to ask is always, “do the economics make sense”. Below is Peter Huber’s excellent discussion of this topic.

When looking at ethanol specifically the more relevant question from an oil dependence perspective is “how much petroleum goes into making a gallon of ethanol”.  If one is looking at it from an environmental perspective, the question would be “how much coal, natural gas, and oil goes into making a gallon of ethanol.”  The total energy input is not a concern since a large part of the energy that goes in to making a gallon of ethanol is the solar energy that goes into growing the crops.

Here is a presentation of a comprehensive Argonne National Lab study that shows these numbers for corn ethanol – note especially slide #12.

Most U.S. studies, by the way, completely ignore the sugar cane equation. The numbers for sugar cane are 5 times better than for corn: Brazilian ethanol production uses practically no external energy input beyond that of the crop itself – even the electricity used the dehydrate the ethanol is generated from bagasse (the sugar cane waste.)

The biggest beater on the ethanol energy balance drum is David Pimentel of Cornell, who is addressed in a brief DOE summary of studies on this issue.

Excerpt from “Thermodynamics and Money” by Peter Huber, Forbes 10.31.05:

Energy Return on Energy Invested [Eroei] calculations now litter the energy policy debate. Time and again they’re wheeled out to explain why one form of energy just can’t win–tar sands, shale, corn, wood, wind, you name it. Even quite serious journals–Science, for example–have published pieces along these lines. Energy-based books of account have just got to show a profit. In the real world, however, investors don’t care a fig whether they earn positive Eroei. What they care about is dollar return on dollar invested. And the two aren’t the same–nowhere close–because different forms of energy command wildly different prices. Invest ten units of 10-cent energy to capture one unit of $10 energy and you lose energy but gain dollars, and Wall Street will fund you from here to Alberta.

As it happens, the people extracting oil out of tar sands today use gas from the fields themselves to power their refineries. There’s gas, too, under what has been called Alberta’s “trillion- barrel tar pit,” but it’s cheap because there’s no pipeline to deliver it to where it would be worth more. As an alternative to gas, Total S.A., the French oil giant, is thinking about building a nuclear power plant to supply heat to melt and crack the tar. But nuclear reactors extract only a minuscule fraction of the energy locked up in the nuclei of uranium atoms; all the rest gets discarded as “waste.” On Eroei logic, uranium would never be used to generate either electricity or heat. But per unit of raw stored energy, uranium is a thousand times cheaper than oil.

Greens touting the virtues of biomass as a source of energy rarely note that almost all of it is used by lumber mills burning branches and sawdust on site. No one cares how much energy the sun “invested” to grow all that waste wood. And every electric power plant, whatever it’s fueled with, runs a huge Eroei deficit, transforming five units of cheap, raw heat into two units of electrical energy. But it all works out because the market values the energy in electricity at about 30 times the energy in coal.

The economic value of energy just doesn’t depend very strongly on raw energy content as conventionally measured in British thermal units. Instead it’s determined mainly by the distance between the BTUs and where you need them, and how densely the BTUs are packed into pounds of stuff you’ve got to move, and by the quality of the technology at hand to move, concentrate, refine and burn those BTUs, and by how your neighbors feel about carbon, uranium and windmills. In this entropic universe we occupy, the production of one unit of high-grade energy always requires more than one unit of low-grade energy at the outset. There are no exceptions. Put another way, Eroei–a sophomoric form of thermodynamic accounting–is always negative and always irrelevant. “Matter-energy” constraints count for nothing. The “monetary culture” still rules.

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