December 12, 2011

Corn Ethanol: How Much Energy Are We Actually Gaining?

Patti Truant

Patti Truant

CLF-Lerner Fellow

Center for a Livable Future

This is the seventh blogpost in “Corn-Fed Cars: On the Road with Ethanol.”

If you’ve been following our On the Road with Ethanol series, you’ve surely picked up by now that there is nothing simple about corn ethanol and its numerous inputs and outputs.  Today, we are tackling the question of energy balance.  That is, when you consider all the aspects of ethanol’s life cycle—from growing the feedstock, producing the fuel, transporting it to the point of sale, to burning the fuel in your vehicle—are we actually gaining energy?  If so, how much?

As you might imagine, there has been much disagreement on this issue and what factors are relevant. While the debate has died down a bit in recent years, it can still be a contentious topic.  Giving a fair hearing to all sides can be difficult, because the methodologies and rationale for including or excluding various factors are not always obvious.

For example, whether or not the energy value of the co-products of ethanol production, namely dried distillers’ grains (DDGs), are factored in may have dramatic impacts on the outcome of a life-cycle assessment (LCA) calculation*.  (DDGs are what remains after the distillation process; they are sold and used in livestock feed.) Also, as we discussed in our last blogpost in this series, the inclusion of indirect land use change (ILUC) as a factor may tip the balance, as it takes into account the impacts of diverting lands, such as cropland or forests, from other uses into ethanol production as well as opening up new lands for food crops to compensate for the shift of other farmlands to corn for ethanol.

While those two factors—DDGs and ILUC—represent the biggest concerns regarding how we assess the energy balance associated with producing corn ethanol fuel, there are many other inputs that really vary with regard to their energy needs throughout the supply chain. Some of these other inputs include the petroleum-based pesticides used to grow the corn, the type of power used at the production facility, and how the feedstocks, and eventually the finished fuel, are transported.

Another way of looking at the question of corn ethanol’s efficiency is to consider greenhouse gas emissions. Last year, the EPA established standards for greenhouse gas emissions reductions of renewable fuels as authorized by the Energy Independence and Security Act (EISA) of 2007, and they did an LCA of corn ethanol, taking into account various types of feedstocks and production techniques . While this LCA was on greenhouse gas emissions and not the energy gains/losses from producing ethanol, the calculation does show that even if you look 30 or 100 years into the future, the benefits of corn ethanol over gasoline depend highly on the production method (some methods actually increase emissions relative to gasoline).  See the EPA’s tables here.

The USDA maintains that while decades ago, corn ethanol was an “energy sink,” it is now a “substantial net energy gain.”  A 2010 report noted gains in efficiency between 2004 and 2008.  The more recent numbers suggest that for every 1 British Thermal Unit (BTU) of energy required to make ethanol, 2.3 BTUs are produced. This is an increase from a 2002 USDA report that found the net gain was a more modest 34 percent.  For more information about what assumptions go into this calculation, take a look at the report by Shapouri et al.  Other types of ethanol production, such as ethanol from sugarcane in Brazil, has been reported as producing about 8 times as much energy than it takes to produce.

Interestingly, the U.S. Department of Energy claims that we are already at a 20 percent GHG reduction using corn ethanol, and while it concedes that a gallon of ethanol provides less energy than a gallon of gasoline, it dismisses the idea that blends up to E10 (the blend currently available at gas stations) reduce fuel economy as a result.  Gallon for gallon, ethanol contains about two-thirds the energy of gasoline.

While our intent here is not to analyze every statistic regarding the energy balance of ethanol, we wanted to convey the importance of taking a critical look at the methods and what factors are considered—or not considered—and who is doing the calculations (industry group, academia or environmental organizations).

In thinking about the costs and benefits of ethanol use, often the factors that are difficult or impossible to quantify—such as soil erosion and water pollution—are not even factored into the equation.  As all of our energy sources become scarcer, it is vital that we improve our methods of producing renewable fuel, but also reduce consumption and improve efficiencies on the demand side.   Also, the reality that ethanol is not destined to singlehandedly provide energy independence or replace foreign oil is one that the corn producers would not want you to face, but is one that is in our best interests to plan for.


*A life-cycle assessment (LCA) calculation puts a numeric value on environmental impacts associated with all the stages of a product’s life, from-cradle-to-grave (i.e., from raw material extraction through materials processing, manufacture, distribution, use, repair and maintenance, and disposal or recycling).

<< Previous blogpost in the series—Indirect Land Use Change and Biofuels: Real or Hypothetical? << 
>>Next blogpost in the seriesThe Cellulose Quandary>>


  1. If you remove the indirect land-use Theroy (it is just a theory), corn ethanol emits 52% less GHG’s than that of conventional gasoline.
    I know your series is on ethanol, but people never consider the amount of energy, water and pollution that is required to drill for oil, refine oil and transport oil/gasoline. Everyone is so critcal of ethanol without looking at how dangerous the alternative truly is on human health.

  2. Pingback: The Cellulose Quandary | Center for a Livable Future

  3. Posted by Patrick Sullivan

    Dear Center for a Livable Future.
    I have both and Agricultural Background, and a Clean Energy Background. So, You are at a disadvantage. The Key Problems here are many:
    I.C.E. Internal Combustion Engine wastes energy approx 40% in the form of Waste Heat
    2. Corn is grown with high imputs that are subsidized via the Dept of Ag/IRS/etc
    3. The Nitrogen Fertilizers are Fossil Based
    4. The Precious Irrigation Water is a what Price Mega Liter? Rare Resource and declining.
    5. Fossil Fueled Equipment/Tractors/Harvesters/Sprays to prepare, sow, and harvest Corn.
    6. Like OPEC, the Corn has an International Value, far to high to use as Stock Feed for Heart Attack Prone Saturated Fat Meat Eaters.
    7. Externalities = Extra Costs from the Healthcare to the Soil Fertility to the wasted fuel because US Cities have suburbs to Racially Divide Neighborhoods.
    8. Perhaps the Solutions is an EV from Tesla, they use renewable or fuelless Solutions like Wind Energy and Solar Energy to recharge Your New EV…

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