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Study concludes that sugar cane-based biorefineries producing ethanol and electricity could power a global auto fleet of hybrids and EVs using only 4% of available cropland

Pacca1
Number of cars (world and US), amount of gasoline consumed, amount of ethanol equivalent required for a neat ethanol fleet, ethanol and electricity to power hybrid fleet, and sugar cane area for hybrid fleet. Credit: ACS, Pacca and Moreira. Click to enlarge.

If sugar cane is used as the feedstock to produce ethanol and electricity for the same final use—fueling vehicles for personal mobility—only 4% of the world’s available cropland area would be sufficient to produce fuels that would power a global car fleet consisting of hybrids and electric vehicles, according to a new study by Sergio Pacca and Jose Moreira at the University of Sao Paolo, Brazil.

In their study, they assess the benefits and drawbacks of the joint production in a sugar cane-based biorefinery—using technology that is currently available and cost-competitive—of 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; their analysis also 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.

Their assessment is 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.)

They also assume that the average yield of a sugar cane plantation is 85 tonnes per hectare (ha) and that 90 L of ethanol are produced per tonne 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 tonne 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.

If all automobiles are replaced by electric vehicles, 697 TWh/year would be required to power the entire fleet in the US and 60 TWh/year would be needed to power the Brazilian fleet. These consumption values are modest when compared to the present electricity use in both countries (3,741 TWh, and 466 TWh, respectively). However, if both ethanol and bioelectricity are used in an optimized proportion, 385 billion liters of ethanol and 262 TWh of electricity would be enough to power the US fleet and, in Brazil, 33 billion liters of ethanol and 23 TWh would be sufficient to operate the fleet for a one-year period.

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.

—Pacca and Moreira

According to their results, based on 2010 values:

  • 2 million ha of land are sufficient to power the Brazilian automobile fleet;

  • 25 million ha are enough to satisfy the needs of the US fleet; and

  • 67 million ha are sufficient to cover the global auto fuel requirements.

  • If minor efficiency gains are considered, 19 million ha will be enough to satisfy the fuel needs of the US fleet in 2030, whereas land required to supply the Brazilian and global fleet remain basically unchanged.

We want to emphasize that we are not proposing that all sugar cane required to fulfill the current mobility scenario be produced in one country. On the contrary, production needs to be spread over several countries that have suitable conditions for cultivation, and in which environmental and social impacts are minimized.

Institution of the proposed schemes requires the development of new policies and regulation on both the supply and demand side. Actions that might be required on the supply side include capacity and institutional building in potential sugar cane producing countries, technology transfer covering biomass and automobile manufacturing, removal of ethanol trade barriers, and the operation of independent power producers. The demand side might require actions that include enhancement of public awareness concerning climate change and the benefits of using sugar cane based energy carriers for transport, and the institution of economic policies that support the acquisition of hybrid vehicles and EVs.

—Pacca and Moreira

Resources

  • Sergio Pacca and Jose R. Moreira (2011) A Biorefinery for Mobility? Environmental Science & Technology DOI: 10.1021/es2004667

Comments

Treehugger

if you need EV to make sugar cane ethanol viable, let's makes EV only and keep the biofuels for the aircrafts. There is not so much lands where you can grow Sugar Cane anyway.

Henry Gibson

Some where ther is an error in this analysis or the way the results are stated. Find the error. There is not much land in the US or the UK that can grow sugar cane. At the rate the land is used for maize ethanol, all of the cropland now used for grains would not produce enough liquid fuels for the US automobiles. ..HG..

Reel$$

Fortunately we will only need liquid fuels for the heaviest lift portions of transportation. Jet fuels, and trucking - even trucking looks like the electric solutions will suffice.

SJC

We could use natural gas or DME made from NG and/or biomass for buses and trucks. I would turn coal plants into IGCC that make electricity and fuels.

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