2.3.1 Transport Biofuels from Terrestrial Plants

Most studies regarding cumulative fossil energy demand have been done for trans­port biofuels from terrestrial plants, and most agree that the seed-to-wheel cumula­tive demand for fossil fuels associated with transport biofuels from terrestrial plants is lower than the well-to-wheel demand of fossil transport fuels. However, Patzek and Pimentel (Pimentel 2003; Patzek 2004; Patzek and Pimentel 2005; Patzek 2006) have presented calculations for cornstarch-derived ethanol, soybean — and sunflower — derived biodiesel and lignocellulosic ethanol that suggest a higher cumulative de­mand for fossil fuels. The difference between these studies of Patzek and Pimentel and other studies is partly caused by difference in allocation, partly by higher es­timates of fossil fuel input in agriculture and industrial processing, and partly by factoring in the energy demand of the infrastructure needed for transport biofuel pro­duction (factories, vehicles, etc.) into the calculations. However, along with assump­tions that are more favourable to transport biofuels, there seems no denying that in western industrialized countries, the cumulative fossil energy demand for transport biofuels made from starch, sugar and edible oils may be quite high when alloca­tion is on the basis of price. For ethanol from US corn or European wheat or rye, it would seem unlikely that, when allocated on this basis, the ‘seed-to-wheel’ cumu­lative fossil energy demand would be much lower than 80% of the corresponding demand for petrol (Hammerschlag 2006; Hill et al. 2006; von Blottnitz and Curran 2007; Reijnders and Huijbregts 2007; Zah et al. 2007). In the case of biodiesel from rapeseed and soybean, qualitatively good estimates usually suggest that, when allo­cated on the basis of price, the cumulative energy demand may well be in the order of 60-80% of the corresponding demand for diesel (Hill et al. 2006; Zah et al. 2007).

Cumulative fossil energy demand for transport biofuels may be considerably lower when biofuels based on high-yielding crops from developing counties, such as oil palm and sugar cane, are considered, especially when lignocellulosic biomass is used for powering processing facilities (von Blottnitz and Curran 2007; Reijnders and Huijbregts 2008a). When the latter applies, for instance, cumulative fossil fuel inputs in ethanol from sugar cane may become energetically less than 10% of the ethanol output (Macedo et al. 2008). Also, much lower cumulative fossil fuel de­mands have been estimated for transport biofuels from lignocellulosic biomass such as wood or switchgrass when processing is also powered by lignocellulosic biomass (von Blottnitz and Curran 2007). When allocation is based on the energy content or weight of outputs, cumulative fossil energy demand allocated to transport biofuels will tend to be lower than in the case of allocation based on price. Note that cumula­

tive mineral oil demand is often lower than cumulative fossil fuel demand, because natural gas and coal can be significant contributors of energy to the transport biofuel life cycle (Hammerschlag 2006; Kim and Dale 2008). For instance, coal is often an important contributor to electricity supply, which is sometimes used by mills pro­ducing ethanol (Kim and Dale 2008). Natural gas is important in production of fixed nitrogen to be used in agriculture (Hammerschlag 2006).