Tidal Current Energy

Biomass
167
in the computation of bioenergy and biofuel production costs. Large-scale international
transportation from bioenergy-producing regions to bioenergy-using
regions will need to be conducted via a broad variety of chains comprising different
biomass pretreatment and conversion operations, and different transportation
avenues for refined biomass [24].
To put biofuels and bioenergy into perspective, with respect to conventional
fossil fuels, Table 9.5 provides the energy densities for some fossil fuels compared
with a typical biomass source, namely wood. As can be seen, in terms of transport
and storage, biomass is at a considerable disadvantage compared with fossil fuels
[26,35]. A comparison of the energy yield on a cost basis with conventional fuel
costs is presented in Table 9.6. The large cost ranges are due to the variation in the
performances of bioenergy systems. For the purpose of this comparison, fossilfuel
processes are assumed to be constant. It can be seen that, in the long term, the
most economic bioenergy system is likely to be the one based on the production of
electricity from wood. This surpasses electricity production from traditional fossil
fuels. On the other hand, on an economic basis alone, bioenergy replacements for
petrol or diesel do not presently appear to compete with fossil-derived fuels [26].
The use of biomass for the production of bioenergy leads to large carbon dioxide
reductions per unit of energy produced, as compared with fossil fuels. Biomass can
Table 9.5. Biomass and fossil-fuel energy densities.
Energy source Energy density/(GJ�t �1 )
Liquefied natural gas 56
Mineral oil 42
Coal 28
Biomass (wood – 50% moisture) 8
(Source: Ref. [26])
Table 9.6. Cost ratios of bioenergy systems compared with conventional fuel costs.
Bioenergy system Biofuel
production cost
(1991 crop prices)
Ethanol production from
wheat (replacing petrol)
Ethanol production from
beet (replacing petrol)
RME production (replacing
diesel)
Methanol production from
wood (replacing petrol)
Electricity production from
wood (replacing grid
electricity)
(Source: Ref. [35])
Estimated future
biofuel production
(based on world
market/lowest price)
Current
context /
(GJ�ha�1�a�1 Future
technology/
) (GJ�ha�1�a�1 )
4.7–5.9 2.9–3.5 2 36
5.0–5.7 4.2–4.5 30 139
5.5–7.8 2.8–3.3 17 41
n/a 1.9–2.2 110 165
1.3–1.9 0.8–1.1 110 165