Energy analysis of sweet sorghum ethanol using a bottom-up energy return ratio matrix approach




Veracruz, John A.

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Between 2012 and 2013 the world increased biofuel consumption by 6.1% and if forecasts hold, according to the International Energy Agency, by 2050 27% of the world’s transport energy will come from biofuels. Rather than succumb to a shortage of corn, alternative feedstocks must gain the same traction corn has gained within the ethanol production industry. When considering an alternative feedstock what must also be considered it is that energy output from ethanol production exceeds the energy needed to produce one liter of alcohol. With origins traced back to Africa, sweet sorghum, or Sorghum bicolor(L) Moench, has gained traction as a viable ethanol feedstock due to the plant’s ability to reach a harvest maturity in as little as four months. With similarities to that of sugarcane, sweet sorghum’s stalk contains a relatively balanced amount of both insoluble and soluble carbohydrates. Although sweet sorghum will flourish with the appropriate amount of water, its drought resistance provides versatility other ethanol feedstocks do not possess. However, lower inputs, drought resistance, and the ability to grow on fallow land are all meaningless if growers miss a relatively short harvesting window, or even worse, allow fermentable sugars to decay by not expediting fermentation. If sweet sorghum ethanol is to displace any amount of corn and prove its feedstock viability, its energy balance must show more energy is output than is input. By using a bottom-up matrix based approach using energy return ratios (ERRs), a product’s system may be evaluated to determine its usefulness to society. The Brandt et al. framework requires the creation of two matrices; a technology matrix, A, and an intervention matrix, B. Devising information from these matrices requires the use of three main vectors which serve as the foundation for calculating the desired ERR. Using this method in conjunction with four ERRs allows the study of energy processes used to create inputs for sweet sorghum pathways and possibly allude to how this energy is used to eliminate waste or improve efficiency through cleaner energy sources.


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