As pointed out in Chap. 2, current transport biofuels often have a cumulative seed — to-wheel fossil energy demand that tends to be smaller than the fossil fuels that they replace. The difference with fossil transport fuels is variable. The difference is probably about zero for CH4 from manure in NW Europe; is as yet unlikely to be positive for current algal biofuels; is smaller than 40% for ethanol from European wheat, biodiesel from European rapeseed or ethanol from US corn and is relatively large for palm oil biodiesel and ethanol from sugar cane, especially when processing is powered by agricultural residues. When the latter applies, the difference may, for example, become greater than 90% for ethanol from sugar cane (Macedo et al. 2008). The overall solar energy conversion efficiency of biofuels suitable for use in internal combustion engines is probably around 0.2% or lower, and expected yield increases per hectare are in the order of roughly 1% per year (cf. Chap. 2). This means that to displace substantial amounts of fossil fuels, land requirements for such transport biofuels are large, as also noted by Dukes (2003).

The contribution that biofuels can make to the national energy security of a coun­try depends on the magnitude of fuel demand and the land area available for sup­plying biofuel feedstocks. For a country such as Brazil, ethanol from sugar cane can make a significant contribution to national energy security. In the USA, the con­tribution of biofuels to national energy security is likely to be much smaller. The reasons for this are that, if compared with Brazil, per capita demand for transport fuels is larger, per capita land availability is lower and feedstocks such as corn and canola are less efficient converters of solar energy into biofuel than sugar cane. Eaves and Eaves (2007) have a point when they argue that devoting 100% of US corn to ethanol, while correcting for fossil fuel inputs, would displace 3.5% of gasoline consumption, ‘only slightly more than the displacement that would fol­low from properly inflated tires’. In fact, they may even have been too optimistic, because the actual US policy has been using a federal excise tax, making mixtures of conventional gasoline and ethanol cheaper than conventional gasoline, which has an upward effect on overall transport fuel use (Vedenov and Wetzstein 2008). Di­verting all 2007 US soybean cultivation to biodiesel production would cover ap­proximately 2% of US diesel demand, when corrected for fossil fuel inputs and assuming no effect on fuel prices (Bagajewicz et al. 2007; Reijnders and Huijbregts 2008b).

Larger displacements of fossil fuels while using the same area of land can be achieved when biomass is burned in power stations and used for electric traction, as the seed-to-wheel overall solar conversion efficiency thereof is higher than in the case of transport biofuels such as biodiesel and bioethanol, as indicated in Chap. 2. However, as explained in Sect. 1.6, such a strategy is dependent on a major change in social acceptance of plug-in vehicles. The potential for energy security through national transport biofuel supply is low for industrialized countries with high pop­ulation densities, such as Japan and the Low Countries in Europe. For instance, in the Netherlands, a 20% target for the share of transport biofuels in current transport fuel consumption would require an area of arable land that is roughly four to five times the size of current agricultural land in that country when ethanol from starch and sugar and biodiesel from vegetable oil are used and when a correction is made for the cumulative fossil fuel inputs in the biofuel lifecycles.

Not only the land area available, but also other factors may limit the extent to which countries may rely on domestically produced biofuel feedstocks for energy security. Climatic change may well have a negative impact on agricultural yields in the developing world (Jepma 2008). As pointed out in Chap. 3, water requirements for producing substantial amounts of biofuel feedstocks are large, and currently, structural water shortages affect about 300-400 million people mainly in Africa and Asia in a band from China to North Africa. Large additional water requirements fol­low from expected population growth and changes in dietary habits, especially the increased consumption of animal produce (Falkenmark and Lannerstad 2005; Liu and Savenije 2008). Assuming business as usual, which does not include a substan­tial production of modern biomass-for-energy, it has been suggested that shortages of freshwater may well become a fact of life for up to 2.5-6.5 billion people by 2050 (World Water Council 2000; Wallace 2002). For instance, water requirements for food consumption are expected to increase greatly in rapidly industrializing coun­tries such as China and India (Falkenmark and Lannerstad 2005; Liu and Savenije 2008). The latter countries are expected to rely increasingly on food export because of limited water availability (Falkenmark and Lannerstad 2005; Liu and Savenije 2008), and this makes it unlikely that they are suitable for large-scale biofuel pro­duction.

Still, in case of major net importers of mineral oil, it may be argued that the availability of biofuels on the world market decreases their reliance on the limited number of countries that are suppliers of mineral oil, and that this diversification may contribute to increased overall energy security. Moreover, one would expect that a substantial production of transport biofuel may have a downward effect on mineral oil prices (Eickhout et al. 2008).

On the other hand, there is the matter of the long-term strategy regarding energy security in transport. Transport biofuels are interesting because they may be used as ‘drop ins’ without a major change in transport technology. But from a long-term perspective, one may argue that major advances should come out of the twin de­velopment of higher energy efficiency in transport (Eaves and Eaves 2007; Royal Society 2008) and supply technologies that are much more efficient than photosyn­thetic organisms in converting solar radiation into usable energy. Using solar cells or concentrated solar power (CSP) to produce H2 for fuel cells or electricity for bat­teries is an interesting example of the latter (Armor 2005; Ros et al. 2009). Though physical conversion technologies such as solar cells presently have higher costs (ex­cluding external costs) than biofuels, it has been argued that in the long run, it may be better to focus on such physical conversion technologies than taking the ‘detour’ of biofuels (cf. Lee and Lee 2008).

The alternative of the twin development of higher energy efficiency and more efficient solar energy conversion technologies will also come up in the context of the next three sections (6.4-6.6) which deal with problems linked to the large areas needed for the production of large amounts of biofuels.