For this assessment we used official data and technical coefficients provided by a very detailed and informative study published by the Sugar Cane Agro-industry Union (UNICA) in Brazil (De Carvalho Macedo, 2005). These data have been checked against the assessment of ethanol production from sugar cane in Brazil provided by Patzek and Pimentel (2005) and Pimentel etal (2007), which were reporting a much worse performance.
Therefore, we used two different assessments of the energy inputs used in the production of ethanol from sugar cane. These discrepancies in the assessments of technical coefficients (different output/input ratios) are relevant for the calculation of the gross/net ratio of ethanol production.
The discrepancies between these two assessments have been investigated by Boddey et al (2008), who report that Pimentel and Patzek assume:
• a larger input for the agricultural production, especially for nitrogen fertilizer (probably because they are sceptical about the possibility of preserving the long-term health of soil producing sugar cane with low inputs of fertilizers) and irrigation; and
• a much larger input for high-tech, heavily mechanized industrial production.
Boddey et al (2008) make the following case:
• Brazilian cane varieties use much less fertilizer than the varieties cultivated in other areas of the world because of the peculiar association found in local varieties with N2-fixing bacteria.
• High-tech production typical of the US has very little to do with the labor intensive production (implying a large recycling of biomass for fertilization) in Brazil.
• The abundant supply of rain implies that in Brazil there is almost no requirement of energy for irrigation.
• The use of bagasse (a by-product of the process) makes it possible to cover not only the requirement of heat, but also the generation of electricity consumed in the production of ethanol.
• Some of the energy conversion factors used by Pimentel et al for phase II are much higher than those used by De Carvalho Macedo.
Because of this combination of fortunate conditions found in Brazil, we can fully appreciate the poor quality of biomass as primary energy source for making liquid fuels, when compared with the quality of fossil energy. In fact, a low use of energy carriers in the production of ethanol does not translate only into a high output/input, but also into a low power level per worker operating in the process of ethanol production (a low EMR).
The opposite is true for corn-ethanol production in the US. Due to the low density of the primary energy input, it uses a lot of technical capital per worker determining a high EMR but this translates into a low output/input energy ratio.
In conclusion, the net supply of ethanol from sugar cane determined by a combination of the intensity per hour of labour and the density per hectare of colonized land remains very low, either when considering an overall output/input of energy carriers of 1.5/1 (according to the high-input assessment) or an output/input of energy carriers of 7/1 (according to the low-input assessment).