sectoral economic costs and benefits of ghg mitigation - IPCC

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There are significant differences in the processing and energy balance depending of the route.
Figure 7 shows energy balance for RFG, for ethanol from corn, for ethanol from sugarcane and
for ethanol from lignocellulosic materials.
As observed, biomass-ethanol produced from lignocellulosic materials is able to transform 1 unit
of fossil fuel energy into 4.07 units of fuel energy, while 1 unit of fossil fuel produces only 0.79
units of RFG to be used in the car. Figure 8 shows that the production of 1 gal of ethanol (i.e.
76,000 Btu) requires input energy in variable amounts depending of the technology in use.
Present technology in use for production of ethanol from corn (dry or wet mill) uses a little over
than 57,000 Btu as input energy, yielding a net balance of 18,000 - 16,000 Btu. Future
technology for corn processing in ethanol promises some slight improvement. Lignocellulosic
material conversion to ethanol (from wood biomass or Herbaceous biomass) is much more
energy efficient yielding a net energy balance as high as 70,000 - 60,000Btu. This means that
input energy is 1/10 to 1/5 of the final energy available in the fuel. As a natural consequence of
this favorable energy balance, GHG emission of ethanol is lower than that of gasoline, even
when accounting for the complete fuel-cycle process. The situation for wood biomass is so
favorable that total emission may be negative when assuming that the by-product residue will be
used to generate electricity displacing coal, as shown for the high alcohol blends E85 and E95
(USDOE, 1999). Results for sugarcane are also presented. Present energy balance evaluation
concludes that one unit of fossil energy yields 8 units of energy as a renewable fuel. Such result
is remarkable, since presently only sugarcane syrup is being used as a raw material for ethanol
production, which represents 43% of the total energy value on sugarcane delivered to mills. 47%
is lignocellulosic material that is already available at the mill and may be transformed to ethanol
using the lignocellulosic conversion technology, improving even further the present energy
balance. On top of that sugarcane residues which are mostly burned before harvesting are being
collected to conform with environmental regulation and can be another source of lignocellulosic
material to be converted to ethanol. Under this favorable situation GHGs emissions for ethanol
from sugarcane tend to be as low as the ones evaluated for woody biomass in Figure 8.
As a real example, with present technology in Brazil the use of 13 billion l of ethanol from
sugarcane abates 9 MtC/yr (Moreira and Goldemberg, 1999).
Assuming ethanol from sugarcane grown in tropical countries is exported to OECD countries to
be used as fuel, the displacement of 50% gasoline could reduce C emission from cars from the
expected amount of 730 MtC/yr in 2020 to 370 MtC/yr, or well below the 460 MtC emitted in
1995.
What is important to consider is that 360 MtC/yr of abatement may be obtained with a sugarcane
planted area 33 times larger than the one being used in Brazil (2.7 Mha) if conventional practices
are used. Based in the best practices commercial results from Brazil (9,000 l/ha/yr), we need only
47.7 Mha of plantation instead of 89.1 Mha. With lignocellulosic material conversion technology
the planted area may be reduced to 30M ha in the near future.
Considering ethanol production cost around US$ 1.00/gal (present cost in Brazil is US$ 0.82, and
the lowest estimated cost from lignocellulosic material based ethanol is US$ 1.00 (CEC, 1999),
when it will be commercially available in USA total annual production cost of 430 billion l is
US$ 113 billion /yr. Assuming gasoline cost at US$ 0.75/gallon and correcting for the lower
energy content of ethanol, ethanol use would avoid US$ 63 billion in gasoline expenditures. Net
cost for using ethanol is US$ 50 billion/yr. Such figure should be compared with other costs for
different alternatives already discussed for limiting CO 2 emission as such:
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