A report issued by Shapouri for the USDA in 1995 concluded that the net energy balance for turning fossil fuels to ethanol was positive, 1.25 to 1.0. Publication of this number would have amounted to a kind of watershed moment in the production of ethanol, establishing it as a 'renewable' fuel source. Since that date, the ethanol-from-corn business has been growing steadily, with over 12 billion liters of ethanol produced in 2004. Most of this is used as an additive to gasoline to boost its octane and help it burn cleaner.
Since 1995 a number of other workers have taken on the work of estimating the net fuel output of the corn-to-ethanol system. The author with the most press is Patzek who wrote Thermodynamics of the Corn to Ethanol Fuel Cycle. (Google it for the web version) In this 120 page report Patzek argues that the amount of energy that goes into the production of corn and the refining of corn into ethanol is greater than what Shapouri estimated. And if he is correct, the production of ethanol from corn may represent a net loss of energy: ethanol derived from corn could actually speed the depletion of oil and natural gas. In the mean time, ethanol has become a big business, and the financial stakes of being right or wrong about these issues gets bigger every year.
The devil, of course is in the details. There are lots of niggling ways in which energy crops up in the cost of a bushel of corn. And it is easy to forget all of them. Similarly, it is easy for a person unfamiliar with the process of turning corn into ethanol to look at corn going in one end, ethanol coming out the other, and imagine that it all happens like magic. But there are a lot of things along the way that eat up energy.
In a strictly mathematical sense, it is vital to know whether the energy yield is greater or smaller than 1.0. If it is smaller, you use more energy than you produce. But in a practical sense, if the number is not greater than 2 or 5, it's probably not a great primary source of energy. Coal, once, was 300. Low quality coal, according to Jared Diamond in Collapse, is around 20 or 30. So while people are quibbling whether corn-to-ethanol is .8 or 1.25, it is essential to realize that so long as the number is less than some pretty big number, 2 or 5 or 10, corn will not be an economically viable primary energy source.
This, however, may not necessarily be the the only determining factor in whether it becomes successful as a commercial product. For instance, if the energy inputs required to create it are cheap but not portable, but ethanol's portability has certain advantages, ethanol might still represent a good fuel for some purposes, such as operating automobiles or farm machinery. Patzek goes to great lengths to provide details about all the places energy is used in the process of growing corn and of making ethanol. But at the end of the day, there are several areas that gobble up most of the energy: Fertilization of the fields, tilling and harvesting of the corn, and distillation of the ethanol.
If we use Patzek's numbers. A hectare of cornfield will produce roughly 30 GJ of energy in the form of ethanol. Of that, roughly 11 GJ would be used in distillation, and 3 GJ would be used as electricity. That leaves 15.6 GJ. But if one totals up the energy that goes to fertilize the field, till it, and harvest it, one finds that this uses about 15.5 GJ (see Table 2) At this point, we have used up more than 95% of the energy provided to us by the corn, and then some. He also charges for other fuel that is used in the normal operation of a farm. Patzek goes on to charge for depreciation of farm capital. He argues convincingly that it takes energy to create and maintain farm equipment and buildings. This, it seems, eats up about twenty percent of the available energy production, and sets the net for the whole activity firmly in the negative zone. At this point the ethanol product contains roughly eighty percent of all the energy required to produce it. He also charges for 'soil mining.' That's an issue that's worth raising. It's hard to argue for or against his argument here. We will address this issue later in a different way.
Patzek has come under heavy fire from pretty much everyone who has the smallest interest in ethanol production, whether financial, political, or intellectual. But he has done us a great favor, because now when we make arguments for or against ethanol, we can make them with an informed opinion. Instead of simply trashing his work, we might ask the question "How could we sidestep the problems he points out?" There are two huge areas that deserve treatment.
The biggest single energy expenditure comes in the distillation process. If it could use waste heat from some primary energy generation process such as a coal-fired or nuclear electric utility plant, then much of the 11 GJ distillation debit would disappear. That would shift the economic equation significantly. In connection with a solid nuclear energy program, for instance, corn ethanol might be a good deal.
The second biggest single loss comes from nitrogenation of the soil. This, it turns out, is an extremely energy intensive activity. Patzek allocates almost 8 GJ to this activity. Nor can this be very unreasonable. Some plants release up to 20-30% of the sugars they manufacture into the soil to support beneficial flora, of which much is to fix nitrogen. In current commercial agriculture, nitrogen arrives at the cornfield as ammonia or as a derivative of ammonia. Ammonia is made from natural gas. Michael Pollan in a Carnivore's Dilemma suggests that 15 percent of Americans' food calories are traceable directly to ammonia derived from natural gas. This number roughly parallels Patzek's. So important is nitrogenation to the success of corn as a crop, that Aztecs held annual mass human sacrifices and used the carnage to fertilize the fields. In our case we send youths to fight in oil-rich areas to secure the resources to cultivate corn. And if we manage our civilization as did the Aztecs we might reasonably expect the same end.
It is possible to fertilize the soil in other ways. One way involves crop rotation. People did this before nitrogen fertilizers became available after WWII. Corn yields then were 20 percent of what they are today. Arguably, much of the difference in corn yield has to do with genetic improvements to the corn. Let us imagine that we could develop crop rotation methods that sustain the fertility of the soil at the level it is now using fertilizers derived from petroleum.
Rotation of crops can help nitrogenate the soil. Certain bean crops fix nitrogen. One of them is soybeans, which is another important crop in commercial agriculture. Other nitrogen-fixing crops include lentils and alfalfa. The problem, of course, is that a field committed to growing lentils cannot grow corn. And that begins to be a problem once we commit vast portions of America's farmlands to the task of fueling our cars. A field that is now planted three years in four with corn, might be planted one year in two or one year in three. Either corn production falls by a huge margin, or many more acres are planted with corn. And there is not that much good, arable land left unused in the US. Under current practice we woud face a trade-off: if we want more sustainable corn agriculture, we might have to settle for less corn, perhaps 50% less. That does not leave a heck of a lot of corn to make into ethanol, not so long as we use corn to feed both cows and people.
There is a second area to explore, the corn that is used to make ethanol and the corn that is used to make corn starch and sweeteners generates corn gluten as a byproduct. It is a rich source of nitrogen, and it could partially make up for the loss of petroleum-generated nitrogen. Patzek does not take credit for this. Whatever portion of corn is used in such products, we might expect, would deliver back to the soil mostof the nitrogen it once took. Corn gluten is now sold as lawn fertilizer, but it may be usable in cornfields as well. And it might put a material dent in the net energy load that arises from nitrogen. The same can be argued for several of the other fertilizer elements, phosphorous and potassium. Furthermore, corn gluten retards weed germination, so it might be used as an herbicide as well.
Also significant are the fuels that are used to till and harvest the fields. In fact, if one were to believe Patzek's fuel numbers, if corn yields were less than 50% of what they are now, even free distillation would not make ethanol attractive; all the energy would be used in cultivation. We find these numbers a little difficult to believe. But we do know that energy in cultivation is significant; Jared Diamond in Collapse mentions that when farm animals were replaced with tractors, it meant an immediate 20% increase in food output. So the idea that 20% of a farm's output is consumed by cultivation certainly seems like an upper limit, but it is not out of the question. This turns out to be just one more way in which we are "eating oil."
We do not know whether Patzek's numbers are right or not. We do know that they are reasonable. And we do know that they are not far afield from numbers produced by quite a number of other workers and in quite a lot of different ways. To those who are making a business of it today, ethanol from corn may seem like a good deal, but all of the authors of the several papers suggest that it is so only by virtue of various agricultural subsidies that artificially depress the cost of corn. When we look at the big picture, ethanol derived from corn might be a very attractive gasoline additive, but as a primary source of energy - given the current state of the refining technology, it is a really bad deal. Using the current state of the technology, if today we had to make ethanol from corn and we had to make corn from ethanol, we would be screwed.
Patzek, curiously, fails to present Tables that show his summary data for energy inputs and outputs. We have taken his data, culled out some of the less important entries, and arranged it to make a little more sense. Because of our treatment, our bottom line numbers will differ from his, but our conclusion is materially the same. Ethanol from corn, given current cultivation and distillation practices is not renewable. It is not sustainable. It is not a good idea as a primary fuel source.
Table 1
| Energy | Application Rate | Energy Rate | Comment - How to make it smaller | ||
| MJ/kg (gal) | kg(gal)/ha | MJ/ha | |||
| Nitrogen | 54.0 |
148 |
7992 |
Crop Rotation, Corn Gluten recycling | |
| Calcium | 1.75 |
333 |
583 |
||
| Phosphorous | 6.8 |
62.5 |
425 |
||
| Potassium | 1.75 |
333 |
583 |
||
| Herbicides | 261 |
2.54 |
662 |
||
| Insecticides | 268 |
1.08 |
289 |
IPM | |
| Gasoline | (46) |
(29) |
1334 |
||
| Diesel | (46) |
(80) |
3680 |
Skeptical it is quite this large | |
| Total | 15548 |
Table 2 Accounting for Energy Flows
| Bushels/ha | gal ExOH/Bushel | l ExOH/ha | Energy Rate MJ/l | OutputMJ/ha | ||
| Corn & Ethanol Yield | 120 |
2.4 |
1036 |
29.7 |
30792 |
|
| Refining Debit | 14.6 |
|||||
| Net Energy From Corn | 15.1 |
15655 |
||||
| Farming Debit | 15548 |
|||||
| Net | 107 |
|||||
Copyright: Stephen R. Brubaker, 2006. All Rights Reserved