Many people see biofuels as a promising replacement for oil in transportation applications. Indeed, being able to replace the oil that contributes to climate change and must often be imported from nasty regimes with carbon-neutral fuels from domestic crops has a great deal of intuitive appeal. For this process to be worthwhile, however, there is a need to consider both life-cycle energy usage and net carbon emissions.
A study conducted in 2004 by Isaias de Carvalho Macedo at the University of Brazil focused on the production of ethanol from Brazilian sugarcane. This is considered by the majority of commentators to be the most energy efficient source of biofuel currently available. This is because most Brazilian sugarcane requires no irrigation and must only be ploughed up and replanted once every five years. The Macedo study found that producing a tonne of sugarcane requires 250,000 kilojoules of energy. This represents the need for tractors, fertilizers, and other elements of modern mechanical farming. The ethanol from one tonne of sugarcane contained 2,000,000 kilojoules of energy. Furthermore, the plants that produce it burn bagasse (the pulp left over when sugarcane has the sugar squeezed out) and can contribute net electricity to the grid. Corn ethanol (the kind being heavily subsidized in the United States) takes about as much energy to grow as is ultimately contained in the fuel.
In terms of net carbon emissions, cane ethanol is also fairly good. Using one tonne of ethanol instead of the amount of gasoline with the same energy content produces 220.5 fewer kilograms of carbon dioxide, when all aspects of production and usage are considered. Burning one litre of gasoline produces about 640 grams of carbon dioxide. Since ethanol has about 25% less energy than gasoline, the relevant comparison is between 1,000 kilograms of ethanol and 750 kilos of gasoline. The gasoline would emit 460 kilos of carbon dioxide, while the ethanol would emit 259.5 kilos.
This is an improvement over the direct use of fossil fuels, but not a massive one. The Macedo study concludes that widespread ethanol use reduces Brazilian emissions by 25.8 million tonnes of carbon dioxide equivalent per year. Their total carbon emissions from fossil fuels are about 92 million tonnes per year – a figure that increases substantially if deforestation is included.
The conclusion to be drawn from all of this is that ethanol – even when produced in the most efficient way – is not a long-term solution. Producing 259.5 kilos of carbon is more sustainable than producing 460, but it isn’t an adequate reduction in a world that has to cut from about 27 gigatonnes of carbon dioxide equivalent to five. Bioethanol may become more viable with the development of cellulosic technology (a subject for another post), but is certainly no panacea at this time.
References:
- Macedo, I. et al. Assessment of Greenhouse Gas Emissions in the Production and Use of Fuel Ethanol in Brazil (prepared for the Government of the State of São Paulo) (March 2004).
- Environmental Protection Agency. Emission Facts: Average Carbon Dioxide Emissions Resulting from Gasoline and Diesel Fuel.
[Update: 8:54am] The above numbers on carbon dioxide emissions produced by gasoline per kilometre are disputed. If someone has an authoritative source on the matter, please pipe up.
See also:
US biofuels: A field in ferment
By: Katharine Sanderson
Nature 444, 673-676 (7 December 2006) | doi:10.1038/444673a; Published online 6 December 2006
Milan,
“Burning one litre of gasoline produces about 640 grams of carbon dioxide.”
You work for EC – where do you get your numbers? Everywhere I check shows that 640 grams per liter is the amount of Carbon in a liter of gasoline. The amount of carbon-dioxide, since it counts the weight of the oxygen, is a lot more. I see a lot of “2.4kg per liter of gasolien” on the internet, but I can’t find a very official looking website. However, I’ve found this one:
http://www.epa.gov/otaq/climate/420f05001.htm
Now, this is american so they use U.S. Gallons which are Imperial Gallons from the 1770’s, which are equivalent to about 3.78 liters.
“Gasoline carbon content per gallon: 2,421 grams
Diesel carbon content per gallon: 2,778 grams”
So, 2421 grams over 3.78 is 640. grams. However,
“to calculate the CO2 emissions from a gallon of fuel, the carbon emissions are multiplied by the ratio of the molecular weight of CO2 (m.w. 44) to the molecular weight of carbon (m.w.12): 44/12.
CO2 emissions from a gallon of gasoline = 2,421 grams x 0.99 x (44/12) = 8,788 grams = 8.8 kg/gallon = 19.4 pounds/gallon
CO2 emissions from a gallon of diesel = 2,778 grams x 0.99 x (44/12) = 10,084 grams = 10.1 kg/gallon = 22.2 pounds/gallon”
8788 grams divided by 3.78 is 2325 grams, or 2.3 kg.
So, in other words, we need to be really clear whether our numbers are Carbon, or Carbon-Dioxide numbers.
Gasoline carbon content per gallon: 2,421 grams
One gallon equals: 3.785 L
2,421 / 3.785 = 639.63 g / L
And thus was the figure found…
This site, which looks neither particularly credible nor particularly dubious, says:
“Here’s a comparison: a gasoline-powered car would emit 2.4 kilograms of carbon dioxide per liter of fuel, and a diesel-powered automobile would release 2.6 kilograms per liter.”
I will try to find some authoritative numbers somewhere.
Another site discussing this
I would keep at this, but I really need to get going.
There is also a related Ask Umbra column:
“Long-haul planes emit fewer warming gases than medium and short-haul planes, because landing and takeoff are the big emissions culprits; long-haulers emit about 32 grams of carbon per passenger-kilometer, short-haulers about 100 g/p-km. The Nobellers show the least-emitting car as a small two-passenger spewing about 20 g/p-km, whereas the most emitting would be a light truck with only a driver inside, at about 99 g/p-km…
The average U.S. car emits approximately 9 kilograms of CO2 per gallon”
Her numbers thus also work out to about 2.4 kg per litre of gasoline.
Note: “The gasoline would emit 460 kilos of carbon dioxide, while the ethanol would emit 259.5 kilos.”
These numbers are not independent of the disputed gasoline/carbon dioxide number disputed above. The relative figures for gasoline and sugarcane ethanol are based on this statement:
“The Macedo analysis suggests that a tonne of cane used as ethanol fuel represents net avoided emissions equivalent to 220.5 kilograms of carbon dioxide when compared with petroleum with the same energy content.”
It would have been far more helpful if they had provided both numbers, rather than just the comparison.
From that EPA site (with metric conversions added):
Tristan’s 2.3 kg / L figure is looking like the correct one. If so, 750kg of gasoline produce about 1743kg of carbon dioxide. The comparative figure for sugarcane ethanol would thus be about 1522.5kg.
On the basis of these figures, the benefits of using sugarcane based bioethanol seem even more dubious.
Heaps of biofuel related posts from R-Squared
R-Squared post on the ethanol v. oil energy balance
Imagining the Future of Gasoline
Biodiesel: King of Alternative Fuels
Daschle and Khosla Ethanol Propaganda
More Ethanol Critics Emerge
E85, M85, or Gasoline?
Recent Damning Biofuel Studies
Bio-Butanol
The Problem With Biobutanol
Ethanol/Alternative Fuel FAQ
Guest Post on Cellulosic Ethanol
Biodiesel Misconceptions
IEA Bioenergy has recently publicized a report entitled “Sustainability of Brazilian bio-ethanol”. The report was commissioned by The Netherlands Agency for Sustainable Development and Innovation, and is in my opinion the most important endorsement of Brazilian ethanol to date. The work was conducted by the Copernicus Institute at Utrecht University in the Netherlands and at the University of Campinas in Brazil. The 136-page report is publicly available here (1.2 meg PDF).
Milan,
the confusion seems to be coming because you equivocate “Carbon” with “Carbon dioxide”.
These things are not equal.
Also, “The average U.S. car emits approximately 9 kilograms of CO2 per gallon”
wtf, if someone can find me a car that produces one molecular weight more C02 per gallon of fuel they’ll have made an error of experimentation. Actually, that might not be true depending on the relation of the energy released by the fuel divided by the speed of light squared.
the confusion seems to be coming because you equivocate “Carbon” with “Carbon dioxide”.
These things are not equal.
Very true.
Indeed, there are four distinct quantities to consider:
Part three is even more complex because CO2 equivalence is not a straightforward conversion. It includes both the global warming potential of each gas in the mix and the duration of that gas in the atmosphere. You can have two mixtures with the same carbon dioxide equivalent, one of which will have no effect in ten years and the other of which may persist for hundreds.
wtf, if someone can find me a car that produces one molecular weight more C02 per gallon of fuel they’ll have made an error of experimentation.
What do you mean here? The figure of 9kg of CO2 per gallon of fuel is consistent with your own calculation of about 2.3kg per litre.
Ethanol is a prime example of a product with what Lee Schipper, an energy and transportation expert at the World Resources Institute, calls “closet carbon.” That is, carbon dioxide embedded in the production of what is supposedly a renewable product.
Over 100 miles, then, the Toyota Corolla will consume 3.23 gallons of gas, which in turn produces 63.11 pounds of carbon dioxide. (According to the Energy Information Administration, a gallon of gas produces 19.564 pounds of carbon dioxide—yes, seriously.)
A recent analysis by Automotive Testing and Development Services found that for every 100 miles of travel, a Tesla Roadster needs to be recharged with 31 kilowatt hours of electricity. (Only about 70 percent of that charge goes toward creating motion; the rest is lost due to inefficiencies in the charging process.) Generating a kilowatt hour of electricity produces an average of 1.55 pounds of carbon dioxide, which means the Tesla vehicle emits 48.05 pounds of CO2 per 100 miles
From Slate
One tonne of C02 is released by the burning of:
432L of gasoline
366L of diesel
391L of kerosine
54 m^3 of natural gas
0.27 m^3 of anthracite coal
The case of Brazilian sugarcane ethanol deserves special mention. It is often quoted as having an EROEI of 8 to 1. I have even repeated that myself. But this is misleading. This measurement is really a cousin of EROEI. What is done to get the 8 to 1 sugarcane EROEI is that they only count the fossil fuel inputs as energy. Boilers are powered by burning bagasse, but this energy input is not counted. For a true EROEI calculation, all energy inputs should be counted. So what we may see is that the EROEI for sugarcane is 2 to 1 (hypothetically) but since most inputs are not fossil-fuel based the EROEI based only on fossil-fuel inputs is 8 to 1.
What is overlooked by touting the EROEI of 8 to 1 and skipping over the true EROEI is an evaluation of whether those other energy inputs could be better utilized. For instance, that bagasse that doesn’t get counted could be used to make electricity instead. Probably in the case of sugarcane, firing boilers is the best utilization. But the lesson from this digression is to be careful when people are touting very high EROEIs. They probably aren’t really talking about EROEI.
Ethanol in India: Another Brazil
“The highlight of my trip was definitely the tour of the Sanjivani sugar cane plant near Shirdi. This could be a model to the rest of the world (with some exceptions) regarding how ethanol should be produced, as they have the entire life cycle covered.
They take in the sugarcane from local farmers, and they produce sugar. Molasses is a by-product of sugar production, and they ferment that to make ethanol. Bagasse is also a by-product, and this is used to fire the boilers to provide power for the plant. The sludge waste that they produce is composted and mixed with the bagasse ash and given back to the farmers to put on their fields. As far as I can determine, this is an entirely sustainable process. But the bagasse is the key to the entire operation.
I quizzed them quite a lot about the bagasse boilers, and what I was told is that because the process produces very finely ground bagasse (I walked out of the plant covered with bagasse dust), and because the ash content in bagasse is very low – it is an ideal feed for the boilers. Very few sources of biomass fall into the category that 1). It is removed from the field as a part of the cultivation; 2). The resulting process pulverizes the biomass (not only does this make it easy to burn, but it dries easily as it passes through flue gas on the way into the boiler); and 3). The ash content is very low, minimizing maintenance of the boilers. This makes sugarcane ethanol a truly unique production method, and not something that is easily transferred to corn or cellulosic ethanol.”
Don’t Rush to Praise Sugar-Cane Biofuels
Published: May 3, 2008
Annual ethanol usage in Brazil: 0.34 barrels* per personperson
Annual oil usage in Brazil: 4.3 barrels per personAnnual person
Oil supplies more than 90% of Brazil’s energy needs
—
Annual oil usage in US: 24.9 bbl/person
Annual oil production in US: 6.1 bbl/person
Annual oil usage in Brazil: 4.3 bbl/person
Annual oil production in Brazil: 3.2 bbl/person
Consumption and production are:
* Grossly unbalanced in the US
* Fairly balanced in Brazil
So, how can the US be like Brazil?
* By cutting oil consumption by 75%
* Or by quadrupling oil production
Sunday, April 26, 2009
More Brazilian Ethanol Whoppers
There are two take home messages from those essays. First, ethanol provides a small fraction of Brazil’s transportation fuel, not 40% as is often reported. Second, the gap between supply and demand is gaping in the U.S., but very small in Brazil. Hence, ethanol is able to play a larger role in Brazil simply because Brazilians don’t use nearly as much energy as does the average American.
Bioethanol from sugar cane
Where sugar cane can be produced (e.g., Brazil) production is 80 tons per hectare per year, which yields about 17 600 l of ethanol. Bioethanol has an energy density of 6 kWh per litre, so this process has a power per unit area of 1.2 W/m2.
Bioethanol from corn in the USA
The power per unit area of bioethanol from corn is astonishingly low. Just for fun, let’s report the numbers first in archaic units. 1 acre produces 122 bushels of corn per year, which makes 122 × 2.6 US gallons of ethanol, which at 84 000 BTU per gallon means a power per unit area of just 0.02 W/m^2 – and we haven’t taken into account any of the energy losses in processing!
Sugarcane Ethanol
Sugarcane ethanol, especially from tropical regions like Brazil, has some unique attributes that have enabled it to compete on a head to head basis with gasoline pricing. Specifically, during the production of sugar, the bagasse (sugarcane residue) is pulverized and washed many times. Many soluble inorganic constituents that may normally pose an ash problem for a boiler are washed out in the process. What remains after processing is a pretty clean biomass feed for the boilers. The normally vexing logistical issues aren’t there because the biomass is already at the plant as a result of the sugarcane processing. So they essentially have free boiler fuel, which minimizes the fossil fuel inputs into the process. The enables ethanol production that is relatively cheap, and that is largely decoupled from the impact of volatile fossil fuel prices.
There are several reasons we don’t do sugarcane ethanol in the United States. Last year I made a visit to the largest sugar producer in Louisiana, and they explained to me that the economics of their by-product molasses generally favor putting it into animal feed. If they had a year-round growing season as they do in the tropics, it is more likely that the animal feed market would start to become saturated, and conversion into ethanol might be more attractive. Further, a bagasse boiler is a major capital expense, so there needs to be a high level of confidence that in the future ethanol will be a more economical outlet than animal feed. For Brazil, this is certainly the case.
The ultimate downside of sugarcane ethanol will come about if the U.S. and Europe begin to rely heavily on tropical countries for their fuel needs – thus encouraging a massive scale-up. First, ethanol imports don’t do much for domestic energy security. More importantly, it may encourage irresponsible usage of the land in an effort to feed our insatiable appetite for fuel. I think the ideal situation is to produce the sugarcane ethanol and use it locally, rather than try to scale it up and supply the world. In this way, sugarcane ethanol could be a long-term contender for providing fuel for the tropics, but not a long-term contender for major fossil fuel displacement outside of the tropics.
Brazil eyes Amazon sugar cane ban
The Brazilian government has unveiled plans to ban sugar cane plantations in environmentally sensitive areas.
The proposal, which must be passed by Congress, comes amid concerns that Brazil’s developing biofuels industry is increasing Amazon deforestation.
Environment Minister Carlos Minc said the measures would mean ethanol made from sugar cane would be “100% green”.
The government agenda is becoming more environmentally friendly ahead of the 2010 presidential poll, analysts say.
The plans unveiled by Mr Minc would limit sugar cane plantations to 7.5% of Brazilian territory or 64m hectares, and prevent the clearing of new land for the crop.
“Brazil’s sugar companies are lucky to have a natural hedge, in that when the sugar price is low many can produce ethanol instead. This can be consumed by motorists in the domestic market or exported for use in alcoholic drinks or other industries.
The market for ethanol has been growing at 17% a year, much faster than that for sugar, points out Luiz Pereira de Araújo of ETH Bioenergia, another fast-growing sugar firm. Such growth is likely to persist, thanks to increased sales of flex-fuel cars, which can run on petrol or ethanol. What is more, the Brazilian sugar-cane growers’ association is optimistic that Europe and America will eventually reduce tariffs on Brazilian ethanol. If that happens, Brazil’s growers, crushers and distillers will be even happier than they are already.”
Energy in Brazil
Ethanol’s mid-life crisis
The sugar industry produces food, fuel and environmental benefits. How fast it grows may depend on an argument about how it should be regulated
Sep 2nd 2010 | Piracicaba, SÃO PAULO STATE
IT IS what passes for a winter’s day in upstate São Paulo. The sun is blazing from a blue sky feathered lightly with cirrus cloud. In a large, sloping field overlooking the city of Piracicaba, a mechanical harvester chomps through a stand of three-metre-high sugar cane, fat and juicy from months of sunshine. The harvester slices the cane into 20cm chunks and regurgitates them into a 30-tonne trailer moving alongside that will lug them a few kilometres to the Costa Pinto mill (pictured). There the cane is weighed, washed, tipped onto a conveyor belt, crushed and then, depending on market conditions, crystallised into sugar or distilled into ethanol. The woody residue—the bagaço—is burned in two high-pressure boilers that, according to the flickering needle in the control room, are supplying around 50 megawatts (MW) of electricity to the local grid—enough to power half of Piracicaba.
Sugar has been grown in Brazil for 500 years, and the country is by far the world’s biggest exporter of it. But sugar now also forms the nucleus of a new agro-industrial and renewable-energy complex. Biofuels, mainly derived from sugar, are Brazil’s most important source of energy after oil. For a unit of energy, the production and use of sugar-based ethanol generates only two-fifths of the carbon emissions of petrol, and half those of corn-based ethanol, according to the United States Environmental Protection Agency. And bioplastics made from sugar cane are poised to move from the laboratory to the corner store, with the launch of soft-drink bottles.
Yet the industry is struggling to turn all these economic and environmental benefits into reliable revenues. For that it largely blames the government and is duly arguing for a more favourable regulatory regime. But it should watch out. The government, in turn, accuses the industry of wanting to have the best of both the agricultural and energy worlds. It could yet make the industry’s life harder.
Since Brazil relaxed price and production controls on sugar cane two decades ago, its crop has increased by two and a half times. Nearly all the growth has come from large, mechanised farms in the south-central region—hundreds of miles away from the Amazon rainforest. Ethanol output has more than doubled since 2002, thanks to the development of flex-fuel engines for cars, capable of running on either petrol or ethanol indistinguishably. More than half the cars in Brazil now have flex-fuel engines, and that figure should rise to 90% by 2017, according to Marcos Jank of UNICA, the sugar-industry association in São Paulo. In addition, Brazil’s government requires petrol to be sold in a blend of three or four parts to one of ethanol.