Energy and greenhouse gas balances of cassava-based ethanol

Biofuel production has been promoted to save fossil fuels and reduce greenhouse gas (GHG) emissions. However, there have been concerns about the potential of biofuel to improve energy efficiency and mitigate climate change. This paper investigates energy efficiency and GHG emission saving of cassava-based ethanol as energy for transportation. Energy and GHG balances are calculated for a functional unit of 1 km of road transportation using life-cycle assessment and considering effects of land use change (LUC). Based on a case study in Vietnam, the results show that the energy input for and GHG emissions from ethanol production are 0.93 MJ and 34.95 g carbon dioxide equivalent per megajoule of ethanol respectively. The use of E5 and E10 as a substitute for gasoline results in energy savings, provided that their fuel consumption in terms of liter per kilometer of transportation is not exceeding the consumption of gasoline per kilometer by more than 2.4% and 4.5% respectively. It will reduce GHG emissions, provided that the fuel consumption of E5 and E10 is not exceeding the consumption of gasoline per kilometer by more than 3.8% and 7.8% respectively. The quantitative effects depend on the efficiency in production and on the fuel efficiency of E5 and E10. The variations in results of energy input and GHG emissions in the ethanol production among studies are due to differences in coverage of effects of LUC, CO2 photosynthesis of cassava, yields of cassava, energy efficiency in farming, and by-product analyses.

► Cassava-based ethanol substitution for gasoline in form of E5 could save 1.4 MJ km−1
► Ethanol substitution for gasoline in form of E5 reduces a CO2e emission of 156 g km−1
► We examined changes in fuel efficiency of blends affecting energy and GHG balances.
► LUC and change in soil management lead to a CO2e emission of 942 g L−1 of ethanol.
► LUC effects, energy inputs, yields, and by-products explain results among studies.