Jan 152008
Blogging on Peer-Reviewed ResearchWith the Iowa caucuses over, the corn ethanol mania that seized the campaigns of candidates from both major parties appears to have passed. This can only be a good thing, because producing ethanol from corn starch is an ecological and agricultural dead end. But the siren song of biofuels continues to beckon, with cellulosic ethanol from switchgrass now being the alcohol du jour. Cellulosic ethanol has tremendous advantages, not least that if cellulosic facilities are the basis of our alcohol infrastructure then practically any vegetation can be used to supply them. Switchgrass, because it is high in cellulose, simple to cultivate, and can be grown on reserve plots, is a tremendously attractive plant to serve as the backbone for such a system. However, research on the full-scale feasibility and energy output from switchgrass cultivation has been lacking. Last week, that deficiency was addressed when PNAS released a study from the U.S. Department of Agriculture and University of Nebraska claiming that the energy output from switchgrass ethanol was more than 500% of the energy put into making it. The article is open access, so you can go on over to PNAS and read it yourself if you like. The findings of this article are encouraging and promising, but it is the start, not the end, of the necessary research.

Assuming that the production and distribution of a biofuel are feasible—this is not a minor assumption—the ultimate decision of whether we should wholeheartedly pursue biofuel production and if so what approach to use should be decided by the answers to the following questions, based on our strategic and environmental needs:
  1. Does the biofuel produce substantially more energy than is needed to generate it?
  2. Can the biofuel significantly reduce or eliminate our dependence on petroleum?
  3. Do production and use of the biofuel add less greenhouse gases to the environment than they remove?
  4. Does the biofuel produce fewer non-greenhouse pollutants than petroleum products?
  5. Can the biofuel be produced without significant disruptions to agriculture or the food supply?
  6. Are the other negative environmental effects of biofuel monoculture manageable?

Obviously, we want every answer to be “yes”, and a little quick thinking will show that switchgrass scores higher than corn ethanol on questions 5 & 6, with a tie on question 4, and less clarity on questions 1-3. Question 2 doesn’t really get a good answer in this paper (so far the answer is “no”), but questions 1 & 3 are treated, albeit incompletely.

The authors of this study answer question 1 with a resounding yes, claiming that the switchgrass fields produced an astonishing 540% more energy than was used in seeding and maintaining them. Given that it is still not clear whether corn ethanol is capable of breaking even on this kind of energy balance, that seems like an end to the question. It’s important to realize, however, that no energy was actually produced in this study, because no large scale cellulosic ethanol plants actually exist. This would appear to be a significant advantage for corn—although its production is less energy efficient, such production is at least not fictional. The energy numbers and ethanol yields in this study emerge from a computer model based on pilot studies; the efficiency of cellulosic ethanol plants on a large scale, though promising, has yet to be demonstrated. As such, this number should be taken with a grain of salt.

The energy numbers for this comparison also do not appear to include the diesel used in agriculture or any estimates of energy costs involved in transporting the substantial quantities of biomass to ethanol plants. The latter is either totally outrageous or completely fair; one of the uncertainties in treating this question is the infrastructure that would be developed. If most ethanol production ends up in large centralized plants the transport costs will be high and the energy efficiency per year will be less. On the other hand, if ethanol production is distributed to many small local plants the energy costs of transport will be diminished while the costs of start-up in terms of materials, money, and energy will be high. This question is significant and one that needs an answer quickly; fortunately, given ballpark figures for energy consumption and output it should be relatively easy to model computationally. That said, I doubt any two models will agree.

So, this study has many nice things to say about the energy yield of switchgrass ethanol, but no experimental proof. But what about question 3? Here again the authors have nice things to say. Most of the plots were carbon-neutral, with slight deviations up or down in different years. Of course, this is again the result of a model; the final answer will depend to a large degree on how effectively carbon can be sequestered in the soil and how much energy the burning of the lignaceous or woody portion of the biomass can contribute to the production process and energy grid.

However, our joy at finding a carbon-neutral fuel should be tempered by remembering that the problem with greenhouse gases is that they are too concentrated in our atmosphere. This is important, so I will repeat it in larger text with a color accent:

The problem with greenhouse gases is that they are too concentrated in our atmosphere.

That is to say, the problem is not that we are adding more greenhouse gases, the problem is that the atmosphere has too much greenhouse gas already. While adding more certainly makes that problem worse, adding nothing does not make it better. Those poor plants and animals got buried underground and hid their carbon away from the world for millions of years; until we put it back where we got it, our climate will be altered. Thus, what we require is permanent sequestration, something that cannot be achieved to any meaningful degree by biofuels.

I’m being mean to switchgrass, of course. Every biofuel fails this test, but so far switchgrass comes closest to success, and the most optimistic estimates certainly seem to indicate that a substantial quantity of carbon would be sequestered in the soil. As the transit system switched over to renewable fuels that advantage would be increased. Biofuels can stop or slow global warming, but they cannot turn back the carbon clock.

So, is this study worthless? Not by a long shot. However, the real contribution of this study is not in its publicized conclusions: they are largely based on modeling and possibly overstated. No, the great contribution here is the substantially more detailed assessment of the required inputs for producing switchgrass biomass on a large scale. The ratio of inputs to outputs was far smaller than expected; from this work it appears that switchgrass cultivation will be more energy-efficient than previously suspected. However, even in this regard the study is limited: the geographic area studied was small and not particularly diverse in climate. It remains to be seen whether switchgrass cultivation will be as effective in warmer or drier climates.

Nonetheless, this study, and others like it, are precisely what we need: detailed research dedicated to finding the best answer. Yet this sort of critical assessment will be all too infrequent in the coming year, as bloviating presidential candidates lurch from hot topic to hot topic, and our useless, brainless Congress lards the budget with pork based on speculation rather than research to find facts.

M. R. Schmer, K. P. Vogel, R. B. Mitchell, and R. K. Perrin, “Net energy of cellulosic ethanol from switchgrass.” Proceedings of the National Academy of Sciences 15 January 2008 pp. 464-469 DOI: 10.1073/pnas.0704767105

 Posted by at 3:00 AM

  4 Responses to “Ethanol from switchgrass: the answer?”

  1. You are completely forgetting that Global Warming is caused by terrorists that are funded by big oil in a giant Zionist Ponzi scheme created by the monk Rasputin to over throw the Tsar! Plus, using anything but diesel or gasoline in your car makes the baby Jesus cry.

  2. You may have missed (as I did) the butanol-making bacteria paper that came out over xmas:


    PS1: Bring it on Rasputin, Vlad Putin will eat you for breakfast..

    PS2: Did anyone take care of my plates??

  3. Unfortunately the bacteria need refined sugars as starting materials at this point. Use of custom organisms to achieve fuel production is of course the best possible outcome because it minimizes energy inputs and theoretically could allow almost any kind of material to be used as a fuel source. However, we're a long way away from that at present.

    JV took care of your plates.

  4. Also, one of my company's customers is working on this gem of an idea http://www.upi.com/NewsTrack/Business/2008/01/15/algae_has_potential_as_a_source_of_oil/4311/
    Finally, oil I can grow myself in the roommate's nasty shower.

    PS: I looked into Puti-poot's eyes and saw he had a good soul. There's no way he can compare with Rasputin. Plus, did you see how evil he was in the Disney movie? How many movies has Disney made about Putin?

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