Sometimes little facts (that aren’t facts at all) get embedded in the common consciousness as undisputed truths. Some of these are obvious – that water spins in opposite directions in a toilet bowl depending on whether you are north or south of the equator, that glass is a liquid that flows, that airplanes fly because the top surface of a wing is longer than the bottom, making the fluid over the top move faster than over the bottom of the wing. It is fun to debunk these and other “facts” and to think about how they came into existence.
In discussion of climate change and energy, there are also some common “facts” that need revisiting. One is related to ethanol as the use of transportation fuels. It is commonly (and mistakenly believed) that production of corn ethanol is an energy-losing process. That is, you get less energy out of ethanol than was put into growing, harvest, and refining the fuel.
A few years ago, a student and I did a careful study of this “fact”. We reviewed all the available literature at the time and concluded that corn ethanol is, in fact, an energy gaining process. Of course, there is more to the potential of corn ethanol than just energy. So, what did we find?
We looked at various metrics to judge whether it is wise to pursue corn-ethanol replacements for transportation fuel in the U.S. Metrics included energy yield, cropland requirements, water use, impact on food prices, and the potential for pollution reduction. In the end, it was clear that while you gain energy by growing corn for ethanol, there were some other serious problems to choosing this pathway.
First, use of corn for fuel results in an increase in food prices. This increase affects not only people in the country that grows the corn, but also international food markets. We also found that based on data available in 2009, full replacement of the U.S. transportation fuels would require 600% or more of the U.S. corn crop. Obviously, this is an unreachable reality. Finally, if your goal is to reduce carbon dioxide emissions, corn ethanol has limited (but real) impact.
On the other hand, there are better options available than corn. For instance, cellulosic ethanol from plants such as switchgrass, poplars, and other sources, allows one to grow ethanol on marginal croplands so that competition with food crops is reduced. It also allows the growth of ethanol crops with far less water, fertilizer, and energy. Perhaps most importantly, use of perennial crops leads to significant greenhouse gas reductions compared to petroleum or corn ethanol.
There is the complication that refining fuel from non-corn sources is more challenging, but that complication is also a strength. As the technologies continue to improve, non-food based ethanol should improve in efficiency. Currently, perennial-crop ethanol has an energy ratio of about 5.5:1 which means you get 5.5 units of energy out of a process for each unit of energy invested. Also, perennials have a six-fold advantage over corn for reducing carbon dioxide (per acre).
So, should I as a scientist advocate a pathway? I think I will. Corn-based ethanol, while limited in its long term potential as a replacement for petroleum could serve as a bridge fuel. It provides a mechanism for refiners to improve their techniques so that if/when other crops are used, the technologies and infrastructure are in place to transition from corn to cellulosic stocks.
Even with cellulosic ethanol, we will likely never replace all of the petroleum used for transportation fuels, but it can play a role in reducing petroleum usage and improving the climate. This wedge solution, along with other wedges, can chip away at our global emissions while providing farmers with a new revenue stream. At the same time, it would reduce the use of fertilizer and water, improving the local environment.
So, should we discard corn-ethanol outright? No. But we should view it as a testing ground for the real solution of cellulosic ethanol. It is a solution that creates winners everywhere.
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