Study Finds Net Energy of Cellulosic Ethanol from Switchgrass Much Higher Than Expected
07 January 2008
|Comparison of net energy yield (NEY) from switchgrass fields managed as a bioenergy crop; low-input, high-diversity, human-made prairies (LIHD) on small plots; and low-input switchgrass (LI-SW) small plots. Click to enlarge.|
A five-year trial of switchgrass on farmland in the Midwestern United States found that the crop produces 540% more renewable energy as a biomass energy crop for cellulosic ethanol than energy consumed in its production. Previous estimates, based on small scale research plots (<5m2 and estimated inputs) suggested switchgrass would yield a net energy production of about 343%.
Estimated average greenhouse gas (GHG) emissions from cellulosic ethanol derived from switchgrass were 94% lower than estimated GHG from gasoline. Kenneth Vogel at the US Department of Agriculture and the University of Nebraska, Lincoln, and his colleagues report their findings in an open access article in the current issue of the Proceedings of the National Academy of Sciences.
The research team managed switchgrass as a biomass energy crop in field trials of 3–9 ha (1 ha = 10,000m2) on marginal cropland on 10 farms to determine net energy and economic costs based on known farm inputs and harvested yields.
The annual biomass yields of established fields averaged 5.2 -11.1 Mg·ha-1 with a resulting average estimated net energy yield (NEY) of 60 GJ·ha-1·y-1. Switchgrass monocultures managed for high yield produced 93% more biomass yield and an equivalent estimated NEY than previous estimates from human-made prairies that received low agricultural inputs.
One of the prime reasons for the improved yield was the actual lower energy inputs for biomass reported in comparison to the estimates previously reported. This highlights, the team noted in their paper, the “discrepancies that can occur when analyses are based on small-scale research plots and misassumptions.”
Cooperating farmers in the project were paid for their work and land use and documented all production operations and field biomass yields. The study provided five years of production and management information from each farm, which the researchers used to estimate net energy, petroleum inputs to ethanol outputs, and GHG emissions.
For an alternative transportation fuel to be a substitute for conventional gasoline, the alternative fuel should (i) have superior environmental benefits, (ii) be economically competitive, (iii) have meaningful supplies to meet energy demands, and (iv) have a positive NEV. The results of this study demonstrate that switchgrass grown and managed as a biomass energy crop produces >500% more renewable energy than energy consumed in its production and has significant environmental benefits, as estimated by net GHG emissions as well as soil conservation benefits.
It is expected that biomass conversion rates will be improved in the future because of both genetic modifications of biomass feedstocks and improvements in conversion technology, which should result in improvement in net energy for switchgrass.
Only a fraction of the research effort that has produced...significant improvements in corn genetics and management has been available for switchgrass and other potential perennial herbaceous biomass species. This is a baseline study that represents the technology available for switchgrass in 2000 and 2001, when the fields were planted.
...It is expected that further improvements in both genetics (hybrid cultivars, molecular markers) and agronomics (production system management practices and inputs) will be achieved for dedicated energy crops such as switchgrass, which will further improve biomass yields, conversion efficiency, and NEV. As an indicator of the improvement potential, switchgrass biomass yields in recent yield trials in Nebraska, South Dakota, and North Dakota (36–38) were 50% greater than achieved in this study.
Schmer, M. R., Vogel, K. P., Mitchell, R. B. & Perrin, R. K. “Net energy of cellulosic ethanol from switchgrass”Proc. Natl. Acad. Sci. USA 105, 464-469 (2008)
Now, add this to UCLA's new e. coli microbes to make isobutanol. And you have an energy croup that can readily replace gasoline, especially with with further efficiency improvements in drivetrains.
It's nice to see some good news like this.
Posted by: Cervus | 07 January 2008 at 05:20 PM
Energy independence in 10 years!!!! Vote Huckabee!
Posted by: ejj | 07 January 2008 at 05:36 PM
I love this, "switchgrass biomass yields in recent yield trials in Nebraska, South Dakota, and North Dakota (36–38) were 50% greater than achieved in this study" in which they got yields greater than 540% of energy consumed! Did I read that right, that current yields should yield more than 8 times the energy consumed? In the Dakotas, land of no rain and long winters? This is phenomenal!
What is the catch?
My Mother ranches in southern Montana, 7000 acres to run 200 cow/calf pairs. She has almost enough precipitation, most years, (about 11 inches) to irrigate 100 acres of alfalfa and to keep the range in decent enough shape that she doesn't need to buy much feed. Man, if she could cultivate Switchgrass...
Posted by: Ziv | 07 January 2008 at 06:09 PM
The catch: Assumed ethanol production numbers, since nobody knows how to make cellulosic ethanol (just yet). So, while this study helped define certain parameters, the complete result should be ingested with a grain of salt, since the overall result is based on a number of "estimates", aka fudge factors.
Posted by: Engineer | 07 January 2008 at 07:16 PM
If Range Fuels can gasify forest waste and make ethanol, maybe someone can do the same with switchgrass.
Posted by: sjc | 07 January 2008 at 07:36 PM
Nice study from an agronomy perspective; they used field trials rather than test plots. Still the conclusions reached seemed fuzzy in terms of estimates for energy return and GHG emissions.
Also, they were quite circumspect about the biomass conversion being a BTL (Biomass To Liquid fuel) process. One might suspect that this is another part of the Syngas campaign that somebody sure wants to get started.
Receive sufficient endorsement based upon acceptance of modelling and optimal testing to get the go ahead. When concern fades and people forget, then open those babies up full bore -- stoked with high profit feedstock, e.g., pulverized coal, waste oil, etc.
Just make sure that the green gas caps given away are NOT made with child slave labor, that the inspectors get the clear message a Strong Country Needs Energy, by gum, and have the spin doctors ready to talk about necessities if there are any scandals about the actual tonnes of carbon equivalents being produced.
Posted by: jcwinnie | 07 January 2008 at 07:41 PM
Hate to rain on your parade, yes thes numbers are very encouraging when compared to the marginal to negative no's previosly for the various feedstocks on low to marginal lands.
Another way of looking at it goes this way. We can grow 1 acre of higher *8 energy input crops per acre of switchgrass harvested. But not an acre of something requiring more than eight times that input If for instance ( Here I havent got any good numbers) ie cotton (water fertilize spray, harvest processing, transport farm labor) or corn fertilizer, sprays machinery.
I could accept, but like clarification that the gasoline equivalent is in fact a finished gasoline product ie in a fully processed or liquid form.
Given the best case scenario as average with environmental advantages.
The problem is that these acre inputs are very low.
Thats great, but most farming inputs are at the other extreme ie very high so the leverage, multiplier what have you is off a low base. Therefore the benefits while apparently very usefull will need to be seen in the context of the volumes that are to be offset.
High input farmlands if food production or prodigious fuel consumption if for that market.
Remember that keeping people on their farms with all mod cons will have a cost too. Not that they wont have costs elsewhere , but remote living can be quite an E consumer to do well also.
Posted by: arnold | 07 January 2008 at 07:42 PM
As far as I know they can make it, it’s just the current procedure doesn’t lend itself well to mass production.
Posted by: Mr. EE | 07 January 2008 at 07:51 PM
The next step is to run a grass farm with onsite surplus fuel production. This is so the tractor runs on alcohol (or whatever), phosphorous and potassium is returned to the soil and no petroleum based herbicides are used. Remember there also has to be enough spare grass and cereal to feed meat animals and make bread. Not just for rural folk but for people with city jobs and their pet dogs. In other words petroleum independent agriculture that produces surplus food and fuel.
Posted by: Aussie | 07 January 2008 at 08:03 PM
The catch, according to an NPR radio broadcast I heard the evening, is that the EROEI in this study is accounted for in cellulose, not ethanol. The energy needed to convert the cellulose to ethanol remains unknown.
As I recall, converting Brazilian sugar cane to ethanol has an EROEI of about eight.
I'm not scoffing at switchgrass, since its EROEI of 5.4 will, even after processing to ethanol, almost certainly beat the EROEI of corn-based ethanol. The corn to ethanol process has an EROEI of about 1.8.
Posted by: John L. | 07 January 2008 at 11:56 PM
@ John L.
Yep. That's the misleading thing on this. How much energy does it take to capture, create and distil the butanol? The UCLA process creates butanol at very low concentration, and slowly...so, the formula isn't high yield just yet.
I don't know if the 50% higher numbers from later farms are directly comparable. Are we talking 50% more tons/acre? Were the inputs 300% higher, thus eroding the EROIE?
All that said, it's a stake in the ground for switchgrass. It's a start. No, I don't want syngas, because it costs too much energy and the more water in the switchgrass, the less EROIE.
Posted by: Healthy Breeze | 08 January 2008 at 01:04 AM
I don't think ADM and the Mega $Billion corn lobby in the Mid-West is going to roll over and die because of this.
Posted by: gary | 08 January 2008 at 06:16 AM
Regardless of these numbers, long term harvesting of cellulose will be tantamount to overgrazing without the benefit of whatever manure that is excreted by the cattle. What nutrients will be returned to the soil to make up for the harvested cellulose?
Posted by: tom | 08 January 2008 at 06:54 AM
Perhaps farmers in the Midwest should start growing switchgrass now to get some experience under their belt. Cellulosic ethanol may not be feasible yet, but biogas is and it can be used to power CNG/ANG vehicles, heat industrial furnaces, produce electricity etc. All of this would help reduce aggregate CO2 emissions and reduce dependency on imported gas. All that's needed is amine-based scrubbing of the CO2 and H2S produced along with the methane. Sufficiently pure methane can be mixed with natural gas in the existing distribution network, once the legal basis for doing so exists (it already does in e.g. Germany and Austria).
The sludge left over after anaerobic digestion into raw biogas contains all the trace elements contained in the feedstock and can be recycled directly as fertilizer. Plants obtain carbon and hydrogen from the atmosphere and water, respectively, so biogas production is sustainable. At $100/barrel of oil and correspondingly high prices for natural gas, it should also be quite profitable by now.
If and when cellulosic alcohol production becomes technically and economically feasible at industrial scales, farmers will have a choice of customers for their switchgrass crop. No subsidies needed.
Posted by: Rafael Seidl | 08 January 2008 at 07:20 AM
Gary, good question! It doesn't seem like a sustainable method unless some inter-cropping was done with say beans that are not harvested/allowed to rot and fix nutes.
JCwinnie, I don't understand a thing you said. try your post again with some better editing. I am curious what you had to say but the way it is written is not legible.
This is good news for sure. It is a tomorrow technology that will get us to the next decade solar technologies that we will surely be forced to rely on for many of the issues brought up in the comments here.
Posted by: energetich20 | 08 January 2008 at 07:24 AM
Someone finally asks the key question...
Posted by: Stan Peterson | 08 January 2008 at 10:38 AM
I was involved in the first anaerobic digestion or reduction process in Vancouver Canada and we could not interst anyone in the technology back in 1978. I have since retired to New Zealand where we intend to use the same basic chemistry to make from algae of which there is no shortage, or either, water, algae and solar power. What we do need are American investors to help run the financial side of the operation. Anyone interested please contact Barry Larkman, VP Development
Aleph Biofuels Ltd at
Posted by: Barry Larkman | 08 January 2008 at 06:48 PM
What they seem to be saying is that you get a lot of cellulose with switchgrasss. Now if you can figure a way to convert it. 300 gallons per acre seems like a conservative number. If you can get 10 tons per acre and 100 gallons per ton, that would be 1000 gallons per acre. BTL gasification has shown that this could be done.
Posted by: sjc | 09 January 2008 at 08:30 AM
"My Mother ranches in southern Montana, 7000 acres to run 200 cow/calf pairs. She has almost enough precipitation, most years, (about 11 inches) to irrigate 100 acres of alfalfa and to keep the range in decent enough shape that she doesn't need to buy much feed. Man, if she could cultivate Switchgrass.."
Most of the rest of you are thinking from the perspective of urban dwellers. The quote above is a most important one, because the study says that the vast acreages in Montana to New Mexico where water is a precious resource and farming is marginal suddenly becomes most practical to raise switchgrass. No irrigation, very low tillage, and end to wind erosion, (google "CRP program") and no annual replanting, with putting the waste back into mulch/fertilizer, make this a most attractive use for all that land.
Currently, grain sorghum is being converted to ethanol in Portales, NM on a scale of several million gallons per year, and that is minor relative to the switchgrass production being discussed here.
Posted by: Bob Russell | 09 January 2008 at 09:52 AM
The beauty of Range Fuel's process is that it would work on almost anything that has carbon in it. If you read up, you'll discover that a few years back they were marketing the process as a CTL technology.
Of course, in the end it will depend on cost. But I'd keep an eye on them...
With a BTL technology you could always return the solid waste (ash/char) from the process to the land, as it would contain most of the nutrients.
Posted by: Engineer | 10 January 2008 at 02:15 PM
The one thing I remember when reading about gasification is that the process needs to be setup for a consistent feedstock. If you have tons of a very similar species of switchgrass, that might be a consistent enough feedstock for the process.
Posted by: sjc | 10 January 2008 at 05:13 PM
define 'forest waste'
Posted by: Bond | 13 January 2008 at 12:05 PM
I am not inclined to define anything because you tell me to. You can look up the terms for yourself as they apply in this context. It seems like you can spell them correctly.
Posted by: sjc | 13 January 2008 at 08:21 PM
As an Australian farmer interested in the potential of this, I assume at first sight that cellulosic ethanol production from feedstock of wheat straw, switchgrass, waste wood, cane bagasse etc would eventually involve local and/or a large number of small-scale on-farm plants to minimise transport costs of heavy raw material. The model here that comes to mind is the wine industry as it operates in Australia at present.
I would be most interested in comments from those more expert in this field than me, which looks like just about everyone participating here.
Posted by: Dixon | 19 January 2008 at 03:10 PM
You are right that the processing plants would have to be close to the biomass to reduce transportation costs. Companies are working on gasification plants that can be located in rural agricultural areas.
I envision a gasifier every 10 miles in rural corn fields in the U.S. turning all the corn stalks and cobs into fuel that gets transported to markets. That way, the corn grain can be used to food and feed leaving the stalks and cobs for fuel.
Posted by: sjc | 23 January 2008 at 09:09 AM