Transport biofuels - a life-cycle assessment approach

Life-cycle studies of the currently dominant transport biofuels (bioethanol made from starch or sugar and biodiesel made from vegetable oil) show that solar energy conversion efficiency is relatively poor if compared with solar cells and that such biofuels tend to do worse than conventional fossil transport fuels as to the emission of eutrophying and acidifying substances. Lifecycle studies of biofuels show diverging results regarding cumulative fossil-fuel demand and the emission of greenhouse gases. If properly done and when allocation is on the basis of prices, cumulative fossil-fuel demand is relatively high for ethanol currently produced from European grain or US maize and relatively low for palm oil or ethanol from sugarcane. The ‘seed-to-wheel’ emissions of greenhouse-gases associated with current transport biofuels are often higher than the corresponding life-cycle emissions of conventional fossil fuels. Transport biofuels vary much in their life-cycle emissions of substances that are ecotoxic or contribute to oxidizing smog.