A life cycle analyst for various types of energy, Roel Hammerschlag, is trying to demystify the great ethanol debate and has systematically reviewed various studies of the subject. Toward this end he has published an interesting paper in the scientific journal
Environmental Science and Technology, a publication of the American Chemical Society, one of America's premier scientific institutions.
I'll just reproduce the abstract:
http://pubs.acs.org/cgi-bin/abstract.cgi/esthag/2006/40/i06/abs/es052024h.htmlVarious authors have reported conflicting values for the energy return on investment (rE) of ethanol manufacture. Energy policy analysts predisposed to or against ethanol frequently cite selections from these studies to support their positions. This literature review takes an objective look at the disagreement by normalizing and comparing the data sets from ten such studies. Six of the reviewed studies treat starch ethanol from corn, and four treat cellulosic ethanol. Each normalized data set is also submitted to a uniform calculation of rE defined as the total product energy divided by nonrenewable energy input to its manufacture. Defined this way rE > 1 indicates that the ethanol product has nominally captured at least some renewable energy, and rE > 0.76 indicates that it consumes less nonrenewable energy in its manufacture than gasoline. The reviewed corn ethanol studies imply 0.84 rE 1.65; three of the cellulosic ethanol studies imply 4.40 rE 6.61. The fourth cellulosic ethanol study reports rE = 0.69 and may reasonably be considered an outlier.
This would seem to suggest that it is likely that the energy balance for ethanol is generally positive, that one
can collect renewable energy profitably from ethanol.
On the other side of the coin, ethanol is something of a tempest in a teapot in the sense that it now produces, even with all this noise, much less than 0.5 exajoules of US consumption, while total US energy consumption itself is well over 100 exajoules. Thus, simply because it has a
positive energy balance does not mean that it is suddenly an unlimited resource that can be scaled indefinitely. All that it means is that it is worth producing
however much can be produced once other factors, such as food, soil and water are carefully evaluated..
There is a commentary in the journal that is available for the public to read, and I think it gives a pretty balanced assessment of the game.
http://pubs.acs.org/subscribe/journals/esthag/40/i13/html/070106comment.htmlI quote:
Farmers grow the three Fs—food, feed, and fiber—for the world. Now, for the first time, they are being called upon to produce a fourth F: fuel...
...Biofuels in the U.S. are produced principally from corn kernels, which are fermented and distilled to ethanol and blended with gasoline as a transportation fuel. Soybeans are processed to form biodiesel, which is often blended with petroleum diesel for fuel. Potatoes, sugar beets, and sugarcane could also be used as feedstocks for ethanol, but presently corn has the lion’s share of the market in the U.S. because of its relatively low price ($2 per bushel). Likewise, soybeans have cornered the biodiesel market, even though canola or most other vegetable oils would do...
...Most biofuel plants are located in the agricultural Midwest, where corn is grown efficiently by rain-fed agriculture and where the co-products (wet and dry distillers’ grains) can be used as local animal feed. Waste from the animals, in turn, is applied on farmland to recycle nutrients back to the land. It is a form of industrial ecology where the waste from one industry (animal agriculture) is used as the nutrient input to another (corn agriculture for ethanol), and the co-products from biofuels production are recycled to feed animals.
Big grain-processing companies love the idea of biofuels. Oil companies hate it. Automobile manufacturers are slowly seeing the greening possibilities through the sale of flex-fuel cars. Most everyone else supports a vigorous campaign to produce more biofuels for greater energy security. But biofuels will also help to curb greenhouse gas emissions, create jobs, reduce our balance-of-payments deficit, support crop prices, and strengthen the farm economy. If the U.S. were more energy-independent, it wouldn’t need to deploy troops to the Middle East to protect oil supply lines; this enrages people there, creates terrorists, and costs tens of billions of dollars per year in taxes. With all those benefits to biofuels, what could possibly be the problem?
BIOFUELS ARE NOT SUSTAINABLE. At least not in the way we practice row-crop agriculture today. Far too many nutrients run off the land, thus causing eutrophication and Gulf hypoxia, and far too much soil erodes for biofuels to be considered sustainable in the long run. We need a cropping system that is perennial, in which tillage is minimized (or nonexistent) and soils and nutrients are held in place...
...Are biofuels a panacea for our energy problems? No. Unfortunately, our gluttony for liquid fossil fuels is so gargantuan that we cannot grow our way out of this problem. The U.S. consumes 21 million barrels of petroleum each day (3 gallons for every man, woman, and child). Even if we utilized all 72 million acres of corn planted in the nation for ethanol and biodiesel, it would satisfy only 10% of our current petroleum consumption. And it would leave us with little room for the other three Fs. Clearly, conservation and energy efficiency are still our greatest energy resources if we choose to get serious about the problem. Wind and solar can help, too.
So we desperately need a new energy mix in the U.S. Food, feed, fiber, and (yes) biofuel will be produced on the farm. But it must be done in a sustainable manner, and it must be part of a comprehensive energy and farm plan. We are not running out of oil, rather we are running out of $50-per-barrel oil.
On balance, the more I ponder the question, the more I favor biofuels with the reservation that we must be realistic about
how much they can do and
where they can do it. I think cellulosic ethanol should be a research area that merits more research and pilot scale evaluation. Ethanol is not going to cut it in Yuma, Arizona, though it may be pretty damn good, barring droughts, in Davenport Iowa. I think we should be happy with
whatever they can do, but accept that they, alone, are
not nationally going to allow this indulgent life style to which we have become addicted.
I think we could do without the mysticism on
both sides of the question.
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