For some applications, biomass as it is produced in solar energy conversion may be used as such. This applies, for instance, to the generation of electricity, which in turn may be used for electrical traction. However, diesel or Otto motors or fuel cells need the use of specific biochemicals (transport biofuels) such as specific alcohols and acylesters, as discussed in Chap. 1. This has an impact on the efficiency of solar conversion. Only a part of the biomass originating in solar energy conversion can be turned into such chemicals. It may be that part of the biomass that cannot be con-

verted into the biochemicals needed is used to power the production from biomass of specific biochemicals. It may also be that a part of the original biomass emerges from processing as waste. Furthermore, in many processes generating biochemicals from biomass, there is an input of fossil fuels that is to be taken into account when determining overall conversion efficiencies. Figure 2.1 gives estimated efficiencies for some conversions of biomass into transport biofuels.

Table 2.2 shows solar conversion efficiencies for a number of biofuels from ter­restrial plants. In this case, the allocation has been done on the basis of energy content of marketable products.

The efficiencies in the last column of Table 2.2 are typically lower than the effi­ciencies shown in Table 2.1. Most of them are below 0.2%. For ethanol from Euro­pean wheat starch, the efficiency is 0.024-0.03%, and for biodiesel from European rapeseed, it is approximately 0.034%. Apart from Jatropha, which has quite an un­certain conversion efficiency, the best efficiency in Table 2.2 is for ethanol from switchgrass, with ethanol from sugar cane coming second. However, it was assumed in this table that in the case of sugar cane, only sugar is to be converted into ethanol. If also a substantial part of the lignocellulosic aboveground biomass of sugar cane is converted into ethanol, sugar cane may as efficient as or better than switchgrass.