The Azimuth Project



Biofuel refers to any sort of fuel that is derived from biomass, meaning material from living, or recently living organisms. Biofuels include solid biomass, liquid fuels and various biogases.

The above chart, taken from this report:

  • REN21, Renewables 2010 Global Status Report, page 24.

shows the worldwide growth in ethanol and biodiesel production. Quoting the report:

Biofuels for transport include ethanol, made primarily from corn and sugar cane, and biodiesel, produced from vegetable oils. Corn accounts for more than half of global ethanol production, and sugar cane for more than one-third. Almost all global production to date has been first-generation biofuels. Biogas is also being used in very limited quantities for transportation in Sweden and elsewhere to fuel trains, buses, and other vehicles.

Biofuels make small but growing contributions to fuel usage in some countries and a very large contribution in Brazil, where ethanol from sugar cane replaces 50 percent of gasoline for transport. The United States is the world’s largest producer of biofuels, followed by Brazil and the European Union. Despite continued increases in production, growth rates for both ethanol and biodiesel have slowed considerably in 2009.

Types of biofuel

There are various kinds of biofuel, each with different qualitative and quantitative features, e.g., operating temperatures, toxicity, pollution from use, etc. For example, they generally have different “minimum teperature for use in an engine” which may need to be borne in mind based upon expected temperatures in the deployment zone. (This and other issues are not necessarily a fatal objection, but need to be planned for.)

The following section is probably an incomplete list (primarily taken from Wikipedia). Expansions are welcome!

There are at least three different axes for classifying biofuels:

1. The basic chemical compound extracted from biological sources

  • Ethanol:

  • Methanol:

  • Butanol:

  • Mixed alcohols:

  • Biogas: apparently essentially methane.

  • Syngas:

  • Solid burnables: e.g., wood, charcoal, etc.

2. The biological material from which the compound is extracted

  • Algae:

  • Sugar cane:

  • Corn:

  • Cellulose/general biomass:

  • Biodigested/landfill decaying municipal organic waste:

  • Biodigested animal waste:

  • Used cooking oil/grease:

  • Carbon compound waste gases from industrial processes:

3. The actual fuel which incorporates the bio-compound

  • Use as a pure fuel:

  • Mixing with petrol/gasoline: sometimes called gasohol, typically denoted by E85, E90, etc, where the number indicates the proportion which is conventional petrol.

  • Mixing with diesel: generally called biodiesel, dominant transportation biofuel in Europe.


Brazil is considered to have the world’s first sustainable biofuels economy and the biofuel industry leader, a policy model for other countries; and its sugarcane ethanol “the most successful alternative fuel to date.” However, some authors consider that the successful Brazilian ethanol model is sustainable only in Brazil due to its advanced agri-industrial technology and its enormous amount of arable land available; while for other authors it is a solution only for some countries in the tropical zone of Latin America, the Caribbean, and Africa.

European Union

In 2006, the EU’s policy target was that biofuels should achieve a market share of 5.75% in the EU by 2010. This blog entry:

responds to some of the points in the consultation documents. The main thrust of the blog entry’s argument was that, based on Eurostat’s own data, Europe doesn’t have nearly enough land to even reach the 6% target. It seems that meeting the EU’s target requires imports — but that moves the environmental impact to Brazil and Indonesia where increased biofuel production may replace tropical rainforest with ethanol or palm oil monocrops.

In 2008, strong doubts that the EU’s biofuels targets were realistic or sustainable began to be voiced by EU and EEA scientific advisory bodies.


David MacKay argues in Without the hot air (p. 43) that biofuels could only generate 0.5W/m2 in Britain, and he concludes:

Even leaving aside biofuels’ main defects—that their production competes with food, and that the additional inputs required for farming and processing often cancel out most of the delivered energy—biofuels made from plants, in a European country like Britain, can deliver so little power, I think they are scarcely worth talking about.

Agrawal and Singh

Since biofuels can be thought of as a mechanism for converting solar energy to usable fuel, their efficiency should be compared with solar power. The following paper makes some quantitative comparisons:

  • Rakesh Agrawal and Navneet R. Singh, Solar energy to biofuels, Annual Review of Chemical and Biomolecular Engineering 1 (July 2010), 343–364.

Overall, biofuels come out looking rather inefficient. However, it should be remembered that biofuels have the additional benefit of coming in liquid form, rather than the form of electricity. For certain applications, notably transportation, this can be advantageous.

Here are some notes on the above paper:

  • A crop growing at the rate of 1 kilogram per square meter per year in the United States, with an energy content of 17 megajoules per kilogram, captures only 0.56W/m2 (0.28%) of the average incident solar energy of 200 W/m2.

(The global average is 156 W/m2. Presumably 200 W/m2 is a US average?)

  • The fast growing crop of Miscanthus (a kind of tall grass) is expected to have a growth rate of 3.7 kg per square meter per year.
  • Even the highly efficient sugarcane crop stores only 1% of the annual incident light as biomass.

  • Zhu et al. have estimated that the maximum conversion efficiency of solar energy to biomass under today’s atmospheric CO2 concentration of 383 ppm and at 30°C is 4.6% for C3 photosynthesis and 6% for C4 photosynthesis. But the highest efficiencies observed across a full growing season for C3 and C4 crops are 2.4% and 3.7%, respectively.

Claims are, however, being made that bamboo will yield 150 tons/hectare/year, 15 kg/m2, e.g. by Bamboo Sur.

Note here that C3 photosynthesis is used by plants that get moderate sunlight and temperatures. C3 plants predate C4 plants, going back to the Mesozoic or earlier. They still make up 95% of plants we see. C4 photosynthesis developed when grasses migrated from the shady forest undercanopy to more open environments in the Oligocene (early Cenozoic). C4 plants do better in conditions of drought, high temperatures, or nitrogen shortage.

  • Algae are considered efficient collectors of solar energy. Under ideal growing conditions, yields in the range of 3–7 kilograms per square meter per year have been reported. A joint venture between ExxonMobil and Synthetic Genomics Inc. aims at getting 1.8 kilograms of fuel (oil) per square meter per year from algae. This is still just 0.9% of the incident solar energy. According to recent projections, it may be possible to grow algae at a rate of 12 kilograms per square meter per year with 30% oil content by mass. Assuming that the oil portion of the algae has the high energy density of 33 megajoule per kilogram, the resulting annual solar energy conversion efficiency of 4.2% is more than twice what’s been demonstrated so far.

  • By contrast, solar power can be turned into heat energy at efficiencies of up to 70%!

  • Or, electricity can be generated from solar power either by a solar-thermal process or a photovoltaic module with efficiencies in the range of 10 to 42%. This is much higher, but we also need to take production costs into account.

  • Commercial photovoltaic modules with efficiencies approaching 20% are already available, and lab-scale multijunction tandem cells have shown efficiencies slightly greater than 40%.

  • H2 can be produced from water by an electrolyzer with electricity to H2 efficiency in the neighborhood of 50%.

(But now we’re talking about converting electricity we’ve already made to hydrogen, so we need to multiply this 50% by the efficiency of the method we used to turn solar power into electricity.)

  • A cute little summary chart.

  • “Because… crop–based liquid fuels, when compared with [using solar power to make] electricity or H2, have so much lower solar-to-fuel efficiencies, we encounter a liquid fuel conundrum”. Namely, the high energy density, 32–36 megajoule/liter, of liquid fuels is tremendously attractive, but making these fuels out of crops is not a very efficient way of harvesting solar power.

(But again, one needs to do some sort of economic analysis to compare the full cost of planting, harvesting, and processing some sort of crop to the cost of alternative methods of harvesting energy! The efficiency percentages don’t tell the whole story.)


S. M. Jordaan and M. C. Moore Ethical risks of environmental policies: the case of ethanol in North America SPP Energy and Environment 3:9 (2010)

S. M. Jordaan Ethical risks of attenuating climate change through new energy systems: the case of a biofuel system ESEP (2007) 23-29

In addition to arguing that the greenhouse gas benefits of biofuel are overstated by many policymakers, the authors argue that there are four questions that need to be considered before encouraging and supporting the production of more biofuel. These questions are: What is the effect of biofuel production on food costs, especially for poor populations? Should more land be used for biofuel when the return of energy per acre is low? Are there better uses for that land? In addition to worrying about the impact of global warming, should we not consider the impact on land of massively expanding biofuel production? What are the other economic impacts of large scale production of biofuel?


For a quick start, try:

Here is an interesting article:

This study estimates the land available for biofuel crops:

The critical concept of the Illinois study was that only marginal land would be considered for biofuel crops. Marginal land refers to land with low inherent productivity, that has been abandoned or degraded, or is of low quality for agricultural uses.

Planting the second generation of biofuel feedstocks on abandoned and degraded cropland and LIHD perennials on grassland with marginal productivity may fulfill 26−55% of the current world liquid fuel consumption, without affecting the use of land with regular productivity for conventional crops and without affecting the current pasture land.

Is it (agriculturally & logistically) possible to use these marginal lands for agriculture? Is it ecologically sound?