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By Robert Rapier on Aug 2, 2008 with no responses

The Lowdown on Miscanthus

Now that Blogger has determined that I am in fact a real person (see this note for an explanation), I am back in business. I notice the Barack Obama is now in favor of my proposal for allowing drilling and using that to fund alternative energy. Just glad I could help. :-) Call me if you need an energy secretary who detests politics and doesn’t respond to direction very well. More on that proposal in a later post, but first there was some topical alternative energy news from a couple of days ago.

A new report from researchers at the University of Illinois suggests that using Miscanthus as a feedstock for cellulosic ethanol production would be far superior to switchgrass:

Miscanthus can meet U.S. biofuels goal using less land than corn or switchgrass

Using corn or switchgrass to produce enough ethanol to offset 20 percent of gasoline use – a current White House goal – would take 25 percent of current U.S. cropland out of food production, the researchers report. Getting the same amount of ethanol from Miscanthus would require only 9.3 percent of current agricultural acreage.

“What we’ve found with Miscanthus is that the amount of biomass generated each year would allow us to produce about 2 1/2 times the amount of ethanol we can produce per acre of corn,” said crop sciences professor Stephen P. Long, who led the study.

In trials across Illinois, switchgrass, a perennial grass which, like Miscanthus, requires fewer chemical and mechanical inputs than corn, produced only about as much ethanol feedstock per acre as corn, Long said.

One finding that I felt was significant:

“One of the criticisms of using any biomass as a biofuel source is it has been claimed that plants are not very efficient – about 0.1 percent efficiency of conversion of sunlight into biomass,” Long said. “What we show here is on average Miscanthus is in fact about 1 percent efficient, so about 1 percent of sunlight ends up as biomass.”

That’s pretty good solar capture for biomass. It is far short of the efficiency of solar cells, but you have a built in storage mechanism – the primary weakness of solar power.

So what’s the catch? Seems like there is always a catch, doesn’t it? The catch is that it is still highly energy intensive to turn this biomass into ethanol. You have energy inputs in growing and harvesting the biomass, getting it to the ethanol plant, converting the cellulose to sugars, fermenting the sugars to ethanol, and then purifying the highly dilute broth to fuel-grade ethanol. That is of course the conventional cellulosic route, and as I have argued before I do not believe this route will ever be commecially viable. The chemistry and physics are strongly aligned against you, which is why we have spent over 40 years failing to crack this nut. That doesn’t mean that companies won’t try to commercialize. They are trying. I just don’t think they will be commercially viable, any more than I think a company is going to cure the common cold in the next 3 years.

Biomass gasification is another story. While the capital costs are still very high, in the long run you may be able to justify growing something like Miscanthus for a gasification plant to produce ethanol, methanol, or diesel. First, though, there is a lot of available waste biomass that could be utilized. Use the waste that is currently rotting or just being burned, and then let’s debate whether or not to dedicate good cropland to growing fuel.