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.

27 thoughts on “The Lowdown on Miscanthus”

  1. Robert, what do you think about water hyacinth for biofuels? Looks like very high annual dry tonnage yield is possible. It’s a tropical crop, but still very interesting, it can be grown in water rather than on land so doesn’t displace terrestrial food production.

  2. “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.”

    Uhm, thats sounds rather incoherent to me.

    Converting sunlight into biomass is somewhere between 3% to 13% at the bleeding theoretical edge.
    With sugarcane around 6-7%.

    And last I checked, Temperate Mithcanthus gets about half the liquid yield per acre than Tropical SugarCane. (Which is more to do with it getting less insolation, than solar efficiency)

    Sugarcane for instance gets around 0.13% solar efficiency to LIQUID once things are all said and done.

    But I have absolutely no idea what they are talking about with those numbers. Are they saying “biomass”, when they mean “liquid”?


    Is this just a mixup? Whats going on?

  3. How much corn stover would be needed to meet the 20% goal? It’s hard to imagine farmers growing switchgrass or miscanthus,except on land unsuitable for food crops. By-products like stover and wood chips will have an advantage when it comes to cellulol.

  4. What happens to the soil after a few generations of this stuff grows?

    I just don’t know the chemistry of it- I know that generally [sun + CO2 + water = biomass] but how much of that biomass came from the soil?

  5. I go back to saying grow the biofuel, then burn it, and fire steam generation power plants with it. Use your GM Volt, and charge up!
    How much liquid fuel will the US need, if our car fleets are EVs?
    Heoric measures to generate liquid fuel from plants may be misbegotten. The Jatropha holds hope, and evidently China is planting millins and millions of hectares of the stuff.
    But I think battery cars are a better idea.

  6. The catch is that it is still highly energy intensive to turn this biomass into ethanol.

    Really? The report says “minimal agricultural inputs”. Burning the plant leftovers for process heat would eliminate the largest energy input. Transport distance is less than corn and planting/harvesting are minor energy inputs.

    The problems with cellulosic are technical. Energy balance should be fine.

  7. ==What happens to the soil after a few generations of this stuff grows?===

    Well, the growing isn’t really a problem.

    It’s the part where you grow it, and then take it away which messes things up.

    Since a significant portion of the nutrients are embodied in the grass itself.

    If you keep taking those nutrients away, it removes nutrients from the soil.

  8. Why not just burn the biomass (waste, miscanthus, or whatever) to produce electricity? Isn’t that going to be more efficient than anything involving extra processing steps? The biomass can be dried for free by the sun.

  9. I don’t think it would be commercially viable, either. I know a little about this plant, as I have a lot of it growing on my land. Even on poor land with no inputs, it grows luxuriously. Much of it is 2 m high when I mow it in autumn. But a big drawback is its rhizome root system, which after a few years wells up, creating humps. This would make it very difficult to harvest with machinery. Also, the roots are extremely tough. If you decide you want to get rid of the plant, you are in for a lot of work. Here in Japan if a farmer wants to rid a field of miscanthus, he typically hires someone with a hydraulic excavator to do it. So it may grow tall and capture a lot of solar energy, but harvesting it after the root systems have developed would present a huge problem. And getting rid of it is very difficult.

  10. I read the links rice farmer. I don’t think those folks realize how much corn stover is fed to grazing cows. I guess the debate will become fuel or cow food. Do you really think all that residue can be turned to organic matter before the next growing season?

  11. First, though, there is a lot of available waste biomass that could be utilized.

    In these days when too many children think that food comes from the grocery store, it is easy for the rest of us to forget (if we ever knew) how much agricultural effort goes into maintaining the fertility of the soil. Hundreds of generations of farmers have built up hard-won lessons about caring for the long-term health of their soil — many of those lessons using what non-farmers call “waste biomass”.

    If we want large-scale dependable post-fossil power, we need to go nuclear. Anything else is an expensive research project, not ready to stand on its own feet economically.

  12. Burning the plant leftovers for process heat would eliminate the largest energy input. Transport distance is less than corn and planting/harvesting are minor energy inputs.

    This gets back to the question “Is that the best use of your energy?” As one poster notes, it makes far more sense to take raw miscanthus and burn it. When you go the ethanol route, you end up producing a highly dilute solution that takes very large energy inputs to purify. This is why I don’t think wet cellulosic ethanol will every be viable. Cellulose does not yield ethanol without a fight.


  13. ricefarmer raises a very good point that I’ve never seen addressed by cellulosic advocates (like our old friend V Khosla), no matter what energy platform is used to produce liquid fuel or electricity. A farmer that commits acreage to growing switchgrass or miscanthus has to make a long term financial commitment, maybe 10 years or more? As he notes, once you plant it, you are stuck with it for at least a while, since it takes 2-3 years to establish, and is also very expensive to establish. Farmers like flexibility in deciding what crops they might grow from year to year so they can take advantage market conditions. And if it’s as hard to get rid of miscanthus as ricefarmer suggests, I’m not sure they will be very willing to take a chance at growing it.

    A small commercial scale biorefinery (say 30 million gallons/yr) will need to have guarantees for biomass production from about 75,000 acres (assumes 5 ton/acre and 80 gal EtOH per ton). Most folks are saying it’s best to use ‘ marginal’ lands for SG or Miscan, and it’s likely that will be maybe 100 acre plots of land or smaller, at best. Those acres will need to be planted to switchgrass at least 2 years before the plant comes on line. The production from those acres also can only be sold to the owner of the cellulosic plant – it would cost too much to ship anywhere else. So the farmer has only viable customer for his product. I don’t think farmers will like that either. Absent huge government subsidies for each cellulosic plant, I can’t envision the way these kinds of acreage commitments might actually get made by farmers. I do think this establishment process would be easier for biomass coburn with coal than for liquid biofuels.

  14. Maury — I have also worked on dairy farms, and I know that stover is fed to cows, typically as silage. In the operations where I helped, the cows ate the silage, and their excrement (and straw bedding) were then applied to the fields. So the nutrient value is not removed from the farm.

    Crop residue does not completely turn to humus in time for the next growing cycle, but you don’t want it to. Organic matter in various stages of decay is good for the land. In addition to providing crop nutrients, it maintains populations of microorganisms and worms, and controls erosion. Compare the fields of farmers who keep plenty of organic matter on their land, and of those who don’t. But don’t take my word for it — ask RR. He grew up on a farm.

    BTW, Oxymaven makes an excellent point about farmers’ need for flexibility. In fact, if you take a look at publications concerned with agriculture, you can see that farmers will often watch the market and wait until the last minute to decide what to plant, and how much. So committing land to miscanthus is a major decision that cannot easily be undone.

  15. Am I missing something?

    Why on earth would you go down the cellulose route when dry miscanthus grass would be perfect feed stock for a BTL plant like the Choren one that RR did an article on recently.

    From that article Choren are producing 18 million litres from about 68,000tons/annum biomass.

    Thats about 264 litres diesel per ton of (assumed) dry biomass.

    As per a DEFRA report, in the UK miscanthus can yield anywhere between 14 to 16 tons (oven dry) per hectare/annum.

    So with, say, 1000 hectares you’d be looking at 68 barrels/day gross output. Or 3.9 Million litres/annum
    N.B. 1000 hectares is ‘about’ 2×2 miles area.
    To keep the above mentioned Choren plant in business you’d need an area of 4.2 X 4.2 miles.


  16. Oh, and another thing, when gasification is used to provide synthetic fuels, the mineral matter (phosphorous/potassium) is left as ash in the gasifier, so surely its simply a matter of cleaning it up and returning it to the fields to close the loop.

    As per the above DEFRA link, miscanthus doesn’t respond to nitrogen fertiliser which suggests its not a nitrogen dependant crop.



  17. Robert, you shouldn’t be so humble, I have discussed energy issues with many folks over the past decade, and few folks seem to have the unbias, realistic, and broad-based viewpoint as do you. I’d campaign for you as energy sec. Energy doesn’t have a path, it follows that of least resistance. Some chase it, others ride it. Too bad politics and bipartisanship act as destructive interference.

  18. Why on earth would you go down the cellulose route

    The U of Illinois researchers claim 370 liters/tonne, quite a bit better than the 264 you quoted for Choren.

    My question for Choren is why use gasification to make liquids? Gasification seems best suited to make gases (duh) and electricity.

  19. Biomass gasification has always seemed promising to me, so long as the mass is near the plant. Kraft pulp mills can take in cheap(sub lumber grade) debranched logs, make pulp, and sell energy back to the grid. Half of the tree is used for pulp and the other half gets burned for electricity. I wonder at the feasiblity of a mobile biorefinery/gasifier. Here in Colorado, we have a tinder box of beatle killed conifer trees, a mobile chipper/gasifier could clean up, redistribute nutrients as ashes and follow the beatle kills, freighting only the finished product(electricity, syngas, biocrude, diesel, etc). It may be good work for the already mobile forest fire fighters. Burlington VT has experimented with some kind of biomass energy conversion facility, anybody know how well it works? It would be really cool if logging operations could use their junky reject wood to make diesel on site, or at the mill, for their machines/trucks.

  20. doggydogworld;

    You’ve fallen for that old trap.

    Comparing liquid volumes. Remember the output of cellulose process is ethanol, whereas Choren is Diesel.

    you need over 1.6 litres of ethanol to equal the energy of 1 litre of diesel, and that’s before the increased efficiency of a diesel engine.

    So that 370 litres ethanol becomes equal to less than 230 litres of diesel.

    Plus the biggest issue, is that like current corn ethanol plants there are significant fossil (nat gas/coal) inputs to distil the ethanol, whereas the Choren type process can export electricity as well as diesel and consumes no fossil fuels.

    Unless the cellulose process has very low capital start up costs then it would appear that its dead in the water compared to the Choren type gasification process.

    If I were an investor I know which one I’d be investing in….

    As for why use gas to make liquids, I’d guess because of a higher profit/unit, or perhaps due to a mandate?


  21. Great article. Here’s an update. Several firms have begun to commercialize giant miscanthus in the US. This after all the news out of Illinois about it. This should allow easier, more cost-effective, and quality controlled growing. The notable one I’ve run across is SunBelt Biofuels Freedom Giant Miscanthus. They’ve branded a high-yielding cultivar from Mississippi State University. 25 tons per acre is the claimed yield, but all yield numbers I've seen for miscanthus blow corn and even switchgrass out of the water.

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