Friday, May 18, 2007

An Assessment of Biofuels.

Biofuels are enthusiastically being sought as an alternative to petroleum-based fuels, in consequence both of a desire to break the dependence of the West on imported crude oil from politically unpredictable regions of the world, and also to counter the simple fact that the world is entering the "Oil Dearth" era, as I have dubbed the time at hand post Peak Oil. In principle too is the added benefit that as a crop grows, it absorbs and fixes CO2 from the atmosphere, and so in an ideal world, the biofuel would be carbon neutral, having obtained all its carbon from this source, merely recycling it in the sense that an equivalent amount of CO2 as is produced when the fuel is burned is absorbed into the next year's crop.

The world, as we are well aware, is not ideal, and there are carbon costs incurred throughout the entire process, from the initial planting of the seeds, addition of synthetic oil and gas-based fertilizers, the final cutting of the crop, the processing of it, the production of the fuel by transesterification (biodiesel) or fermentation (bioethanol), and the final extraction or distillation of the fuel itself ready to be put into "petrol tanks". It is indeed a hotly debated topic just how energy intensive biofuel production is, and much angst pertains over the EROEI for ethanol production for which figures in the range 0.7 to 1.3 have been deduced. Thus for each barrel of oil worth of energy expended in producing bioethanol, 0.7 or 1.3 barrels of ethanol are obtained as a return on the investment: anything below an EROEI of 1 is a loss and above it a profit can be declared.

I have also shown in various postings that it would be impossible to grow enough fuel crops to quench our current thirst for liquid petroleum fuels using biofuels instead, even if we were to stop growing food altogether. There does come the inevitable conflict between growing crops to feed people and animals or cars and planes, as the amount of arable land is relatively quite limited to do so. Nevertheless, the adaptation of the biofuels strategy to break-down and ferment cellulose/cellulosic materials into ethanol or the production of biodiesel by high-yielding algae does offer sufficient promise that I remain hopeful about still being able to produce significant amounts of fuel in the future, albeit through technologies that are as yet unproven on the large scale. Coal-liquefaction is a tried and tested method for making hydrocarbon fuel on a large scale, but we would need to build around 30 combined cycle plants in the UK to produce the equivalent of one third of currently used petroleum fuel, while producing most of the UK's electricity simultaneously.

Since we will begin to run short of gasoline type fuels within a decade, as the sweet (low sulphur) light crude oil will have mostly been exhausted by then, this is the timescale that any alternative technologies need to be installed against, meaning that we need to get cracking. My own view is that either in terms of physical shortages of fuel or their cost, we will never again see the equal of the present energy jamboree, meaning a substantial fall in transportation and a fragmentation of industrialised societies into small communities which I have termed "pods", containing say 10,000 - 20,000 people. If we run out of energy, then forget about nanotechnology and focus on breeding horses and planting fields instead.

Notwithstanding these reservations, let's look at some potential sources of biofuel. Brazil uses sugarcane as the feedstock for an industry that produces 4 billion US gallons per year of ethanol, which covers 40% of the country's fuel requirements. In contrast, the US produces a comparable 3.4 billion gallons of ethanol from corn, but which amounts to somewhat less than 2% of the fuel used altogether by the huge fleet of cars needed to get around in this far more dispersed nation. Europe ranks third in ethanol production, but achieves it using mainly sugar beets, wheat and barley as the "sugar crop". It is interesting that if Brazil meets its plans to expand the arable area used to grow sugar cane from 5.3 million hectares to 8 million hectares, it would become self-sufficient in automotive fuel within only a few years while maintaining its production of sugar and exports of sugar and ethanol. Presently about half the Brazilian sugar cane is used to make fuel and the other half for sugar.

There are two essential criteria for elucidating the relative merits of growing particular crops for biofuel production, namely the fuel yield per hectare/acre and the energy yield of the biofuels. [I would issue a caveat here, e.g. while ethanol has only 70% of the energy that gasoline does, on the basis of the relative heat of combustion of the two fuels, it can be burned more efficiently in specially adapted engines, and so the output power of the fuels is comparable]. For ethanol, the best yields per hectare are 1785 gallons from sugar beets in France and 1655 gallons per hectare from sugar cane in Brazil. In the US, corn yields close to 885 gallons/hectare or about half that from beet and cane crops.

The king of biodiesel is palm oil which may be produced in a yield of 1270 gallons per hectare. Coconut oil comes next at 575 gallons/hectare, and rapeseed at 255 gallons/hectare. However, as I mentioned earlier, as supplies of conventional crude oil fall short, there will be an economic competition between crops for fuel or crops for food, and there is only so much land upon which all of them can be grown. In the line of fire then comes forest land, which increasingly is being cleared to grow palm plantations in Indonesia and Malaysia, and in Brazil to grow more sugar cane to match that expansion to 8 million hectares of land for the purpose, that I referred to. For sure, there will be environmental costs to be paid, even if a compromise can be struck between food production and biofuel production. But until the cellulosic and algae technologies are brought on-line (if they ever are), we will be embroiled in the greatest battle ever - over resources and prices, with casualties on all sides; perhaps this is the real WWIII.

Related Reading.
"People and Fuel Compete for Land,"
The article is based on Lester R. Brown's new book "Plan B 2.0: Rescuing a Planet Under Stress and a Civilization in Trouble," Chapter 2, "Beyond the Oil Peak", published by W.W.Norton, New York, 2006.

1 comment:

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