Sergio Pacca and Jose R. Moreira at the University of Sao Paulo in Brazil have their idea of the best numbers for biofuel out and the numbers are very surprising.  Almost no one is expecting the team’s figures and the recoil might get fierce.

It’s a massive reduction in the amount of land needed to produce a world supply of ethanol.  In the study their analysis shows that the harvested energy density of sugar cane is 306 GJ/ha/yr – – – 1.7 times the value usually reported in the literature for biofuels.

Pacca and Moreira assess the benefits and drawbacks of the joint production in a sugar cane-based biorefinery using technology that is currently available and cost-competitive for making ethanol and electricity for fueling privately-owned automobiles. Their findings indicate that the amount of land required to power current automobile needs is less than what is typically stated.

The rough numbers in the study are based on utilizing a sugar cane mill for energy production; a hybrid automobile powered by an internal combustion engine that consumes ethanol with an efficiency of 15 km/liter (35 mpg US, or 6.67 l/100km), which corresponds to the efficiency of a commercially available automobile assuming 19.55 km/liter (46 mpg US, or 5.1 l/100km) using gasoline as the fuel. They assume the fuel performance (measured as km/L) of the ethanol engine is 75% of that of a gasoline-powered engine.

To get to those fuel numbers the team also assumes that the average yield of a sugar cane plantation is 85 tons per hectare (ha – about 2.5 acres) and that 90 L of ethanol are produced per metric ton of sugar cane. In addition, they assume that the bagasse byproduct will be used as feedstock in boilers to produce electricity and heat. In order to achieve a surplus of 125 kWh of electricity per ton of sugar cane, they require that 50% of the sugar cane straw is also harvested and, together with the bagasse byproduct, is used for power production.

The numbers come in a simple sequence.  As seen in the graphic, 886 million cars would need 1299 billion liters of gasoline or 1688 billion liters of ethanol.  Then 1055 billion liters of sugarcane and the 717 terawatt hours a year of power generation could come from 67 million hectares of sugarcane fields.

Pacca and Moreira Steps to Sugarcane Crop Area. Click image for the largest view.

Thus, only 4% of the world’s available cropland area would be sufficient to produce fuels that would power the global car fleet.

How the team gets to complete energy supply is quite simple if presumptive – “These energy consumption figures equate to a US fleet comprised of 143 million hybrid and 86 million electric vehicles. In comparison, the proportional Brazilian fleet would be comprised of 20 million hybrid and 12 million electric vehicles. Alternatively, the fleet in both countries could consist of only hybrid plug-in vehicles that are powered by ethanol and electricity.”

The study results seem plausible and over time may serve to get estimates on a more realistic footing.  Sugarcane is very prolific compared to other crop biofuel sources and can give algae serious competition.

The only catch from the materials reviewed is the system as proposed plans to use half of the leaf part of the plant that is currently left to the soil for burning with the bagasse.  Bagasse and the leaves research for best use is barely underway.  Burning may be a quite primitive choice soon.

Which leads to another presumption that might not hold.  The fleet mix of hybrid and electric vehicles may need some pressure from either the market or a government intrusion.

The study is available at the American Chemical Society journal Environmental Science and Technology titled A Biofrenery For Mobility?

Let’s hope the other blogs, media writers and other science information users give some thought to the proposal from the Brazilians.  Getting a lower cost per distance traveled in personal vehicles is a worthy goal and the new study provides a path that could get us there much quicker and less economically exhausting than many others.


2 Comments so far

  1. Al Fin on October 25, 2011 9:17 AM

    As much as I dislike ethanol as a fuel, these numbers suggest a great deal of potential for cane alcohol.

    Of course sugar can be turned into all sorts of things, depending upon the fermenting micro-organism. The basic infrastructure of sugar production and bagasse utilization could be used to ferment just about anything that microbes could be made to produce.

    Amyris is involved in Brazil with its synthetic biology microbes, aiming to produce a lot of high value chemicals and materials using cane sugars. Solazyme is also getting involved there, trying to ferment algal lipids from sugar,. to turn into advanced hydrotreated biodiesels.

    We should expect some interesting developments from all of this ferment down in Brazil.

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