Clean, renewable fuel from crops?

Is it possible to grow crops on a farm, and process them into a clean source of energy?

The principle sounds simple enough.

  1. grow sugar cane or beet.
  2. extract sugar
  3. brew into alcohol
  4. distil
  5. profit.

Ethanol burns cleanly, into CO[sub]2[/sub] and H[sub]2[/sub]O. It can be used, for instance, to power vehicles. And it’s carbon neutral, because the plants absorb the same amount of CO[sub]2[/sub] while growing.

Sounds good, in theory. But I always heard that the process takes more fuel than it produces. Until today, that is, when I was informedthat it actually produces 8-10 times more than it uses. Can this be true?

Whats the Dope here? Is ethanol the fuel of the future? is this a practical and clean energy source?

If so, why haven’t ethanol cars replaced petrol ones yet?

Reposting from another thread:

Large NG feature, this has both some articles and interactive graphs and displays. You’ll note that Brazil (nearly 7 years ago), was producing 3.96 billion gallons of ethanol from sugarcane, at a cost of $0.87/gallon. The energy input/output graph for Sugarcane will show that for every one unit of input sugarcane produces 8 equivalent units of output. Basically meaning for every say, BTU of energy consumed to grow, harvest, and process the sugarcane you get 8 BTU back out.

Article in the New York times noting sugarcane varies from 8.3 units of energy for every unit of input to 10+.

This PDF from the World Bank repeats the energy ratio figures on pages 28-29.

After that, you can go to this fairly good wiki article on Brazil’s ethanol industry which contains some 150+ citations to support what is said in the article itself.

I have no idea if it is the fuel of the future, but even corn ethanol (one of the worst ratios) has a positive energy balance, meaning more energy is harvested than is put in as an input. Further, a point of order is that the input energy doesn’t have to be in the form of fossil fuels. It most likely is in this day and age, but it doesn’t have to be. (This addresses an erroneous claim you made in the other thread that without fossil fuel petroleum we’d have no way to even harvest the plant matter.)

It’s not just ethanol for one. Some plants are turned into biodiesel, and biodiesel is coming on strong. Further, I don’t know if you’re genuinely ignorant of this, but in America there is now ethanol in the pumps along with gasoline, often up to 10% of the gas being pumped. I don’t know if you’ve never seen cars with the “Flex” logo on them, but these are Flex fuel vehicles and have become a lot more common in recent years. A normal gasoline car can easily run on a mixture of 90% gasoline and 10% ethanol (yours might even do this if you’re American and drive a gasoline powered car); a Flex fuel vehicle can run on any mixture of the two fuels in various proportions up to 85% ethanol (which is what comes from an E85 pump.)

They’re also trying to make biodiesel from algae - it doesn’t compete with food like corn, and doesn’t need to be grown on farmland.

I made no such claim. Nor would I say that. It is obvious that you could have harvesters that run on ethanol.

Yes, I did know that, in fact. But that does not, in itself, prove that it’s energy positive.

That’s probably the best thing on the horizon right now. It’s still not cost competitive to process it but bio-engineering may give us a diesel and gasoline fuel that needs less processing (and thus cheaper to produce).

It would be nice if this was fast-tracked on a Manhattan Project level because it affects so many different aspects of our life.

In any case, you’ve made a claim based on “something you’ve heard” that you can’t get a net energy positive production of ethanol from biomass. I’ve demonstrated several strong citations that sugarcane ethanol is an 8-10 energy ratio process.

I’ve cited publications from large respected NGOs like the World Bank and respected sources like National Geographic. Unless you have some basis to disprove the net positive energy ratio of ethanol produce from sugarcane, I consider your question asked and answered.

FWIW your first post in this thread makes it seem like maybe part of the reason you are incredulous is because it should be so easy to profit from this method, and the fact this isn’t “that” widespread is perhaps proof that the process doesn’t actually “work” and isn’t a net positive ratio.

Instead all that this is proof of is two things:

  1. We have an entrenched crude oil–>refinery–>distribution network based on gasoline that has lots of economies of scale and such that make it expensive to start up new fuel sources, which retards new fuels to a degree.

  2. Crude oil, for all the hoopla about it being really expensive is really, really fucking cheap, that doesn’t mean sugarcane ethanol isn’t net energy positive, it just means that sometimes it really can be more economically sensible to drill for crude oil and refine it into gasoline than it is to run a big sugarcane farm and harvest the sugarcane then render it into ethanol.

I don’t know, all I’ve heard is from the project proposals, which are always overly optimistic. Look at carbon nanotubes. Are there any products that make good use of them yet?

We ought to find a way to produce biodiesel from the damn Eurasian Milfoil! Or Kudsu.

Some would disagree.

Pimental is a life long skeptic and opponent of corn ethanol. I actually agree with Pimental’s opposition to corn ethanol and corn ethanol subsidies, as a biofuel source corn is one of the worst plants out there. It is soundly trounced by sugarcane, switchgrass, and I think even soybean is better.

Over the past thirty years most people have said Pimental is a crackpot clinging to 30+ year old data to denounce corn ethanol. I don’t go that far, but I do agree with what MIT researchers say:

However, I tend to think the studies that put corn in the range of 1.2-1.4 energy ratio is probably more valid. But yeah, corn has the lowest ratio, so variations in how you calculate input/output can erase its positive energy ration–however the majority of reports published in the past 10-15 years seem to side with corn ethanol being a positive energy ratio.

Pimental basically asserts everything remotely connected to corn production be counted as part of its output, including the energy used at factories that produce farm equipment. That might be the right way to do it, but when people compare it to the crude oil–>refinery process are we factoring in every single possible input in that process? Including the shipyards that build all the tankers and the fuel used by all the tankers, all the factories that create the tools used to build the refineries, pipelines etc etc etc.

We’re getting into stuff I don’t even know about tangentially (I know we have some energy industry people on the boards who would probably know more), but I have to wonder, even if we count things the way Pimental does is that really a problem? I could imagine a scenario in which even if something has a negative energy ratio it could make sense to use it at least for some time. In the original GQ thread that created this discussion, I would say if you had a situation in which you didn’t have crude oil anymore, but you still needed a type of liquid hydrocarbon fuel for special applications (plastics etc) it might still make sense to make it at a “loss”–because the input energy doesn’t have to be ethanol, it could be natural gas, geothermal, electric from a nuclear plant etc.

Or rather, imagine we have a chemical plant to produces a specialty chemical used in medicine that’s very important, the production of the medicine is a net energy loser, but it might still be worth running the chemical plant. So in a hypothetical in which we had no more crude oil, it might still make sense to synthesize oil for any of those special applications where you can’t replace oil as an input.

The principle is sound. The problem is the low yield would not produce enough fuel to replace our use of oil, and the cost would be very high. Even if we reduce oil usage through other alternatives, as long as we have oil, the difference in cost compared to oil will increase unfavorably . This happens because the lower demand for oil will lower it’s price, which is artificially inflated, and can get very much lower as demand decreases.

The approach to reducing oil consumption based simply on the economics would be to maximize the usage of the most cost effective alternate energy source. Whatever alternate technology is least affected by lowered oil demand will have the best chance of surviving competition and utilizing the economy of scale. However, simple profit and loss are not the factors influencing the drive for alternate energy sources. All energy production is subsidized in some way or another, and there are many secondary costs to each. Politics will end up playing a large role in determining the economics of any alternate energy source.

My understanding is that Pimentel has also assumed that any products other than ethanol don’t count. The process today produces a vast amount of byproduct (distiller’s grain) which is used as animal feed. Pimentel assumes that if we scale up, there won’t be any demand for the byproduct, and it’ll be wasted. Even if true, I believe this answers a different question: would ethanol be net energy positive if we replaced all gasoline with ethanol vs. is ethanol production today net energy positive? I think almost all analysis answers the latter question as ‘yes’, though quite close, as Martin Hyde points out.