Emissions Scenarios - IPCC

Scenario Driving Forces 137
3.4.3.3. Conclusion
Comparatively few scenarios in the literature explicitly consider
the inteiplay between resource availability and technological
change, and hence the possibilities of wide-ranging alternative
futures of fossil and renewable resource use. For fossil fuels,
altemative resource development scenarios are described in
Ausubel et al. (1988), Edmonds and Barns (1992),
IIASA-WEC (1995), Nakicenovic et al. (1998a), and
SchoUenberger (1998). For renewable energy resources,
scenarios of enhanced resource development are described in
Goldemberg et al. (1988), Johansson et al. (1993), Lazaras et
al. (1993). Watson etal. (1996), and Nakicenovic etal. (1998a).
A critical issue in the context of this report is how to capture
altemative future 1п1еф1ау8 between energy technology and
resource development, in contrast to the more traditional
approach of assuming fixed resource quantities across all
scenarios. This is important because the literature reviewed
above indicates that resource availability can vary widely. For
instance, generally oil and gas are considered the most
constrained fossil fuel resources. Yet, a representative range
from the literature gives cumulative production levels between
1990 and 2100 of between 21 and 65 ZJ, with typical
intermediate scenarios of 30-35 ZJ (Nakicenovic et al., 1998a;
SchoUenberger, 1998). The extreme values of cumulative
resource use are evidently inversely related between different
energy sources across the range of altemative scenarios. For
instance, in scenarios with high availability of oil and gas,
typically the use of coal or renewable resources is more limited,
whereas in scenarios of rapid development of renewable
alternatives, the use of fossil resources is more limited. In other
words, future resource availability of fossil fuels as well as
renewables is constructed in scenarios based on current
understanding and the available literature. Resource availability
results from altemative policies and strategies in exploration,
R&D, investments, and the resultant resource development
efforts. The long lead-times and enormous investments involved
result in such strategies yielding a cumulative effect, refeiTcd to
in the technological literature as "lock-in" (see Section 3.4.4).
Development of alternatives can be furthered, but it can also be
blocked when policies and investments favor existing resources
and technologies. The most important long-term issue is how the
transition away from easily accessible conventional oil (and to a
lesser extent conventional gas) reserves will unfold. Will it lead
to a massive development of coal in the absence of alternatives
or, conversely, to a massive development of unconventional oil
and gas? Alternatively, could the development of post-fossil
alternatives make the recourse to coal and unconventional oil
and gas (such as methane clathrates) obsolete?
3.4.4. Energy Supply Technologies
3.4.4.1. Introduction
The recent literature on long-term energy and emission
scenarios increasingly emphasizes that both resource
availability and technology are inteiTelated and inherently
dynamic (see, e.g., IIASA-WEC, 1995; Watson et al. 1996;
Nakicenovic et al., 1998a). The state of the art of theories and
models of technological change is reviewed in Section 3.4.5.
The literature suggests that models of endogenous
technological change are still in their infancy, and that no
methodologies are established that reduce the substantial
uncertainties with respect to direction and rates of change of
future technology developments. Differences in opinions as to
the likelihood and dynamics of change in future technologies
will therefore persist. Such future uncertainries are best
captured by adopting a scenario approach. The following
discussion on changes in energy supply and end-use
technologies therefore reviews the literature with emphasis on
empirically observed historical and conjectured future
changes. The principal message is that while the future is
uncertain, the certainty is that future technologies will be
different from those used today. Hence the most unlikely
scenario of future development is that of stagnation, or absence
of change.
3.4.4.2. Fossil and Fissile Energy Supply Technologies
Fossil-fueled power stations traditionally have been designed
around steam turbines to convert heat into electricity.
Conversion efficiencies of new power stations can exceed 40%
(on a lower heating value basis - when the latent heat of steam
from water in the fuel or the steam arising from the hydrogen
content of the fuel has been excluded). New designs, such as
supercritical designs that involve new materials to allow higher
steam temperatures and pressures, enable efficiencies of close
to 50%. In the long ran, further improvements might be
expected. However, the past decade or so has seen the dramatic
breakthrough of combined cycle gas turbines (CCGTs). The
technology involves expanding very hot combustion gases
through a gas turbine with the waste heat in the exhaust gases
used to generate steam for a steam turbine. The gas turbine can
withstand much higher inlet temperatures than a steam turbine,
which produces considerable increases in overall efficiency.
The latest designs currently under construction can achieve
efficiencies of over 60%, a figure that has been rising by over
1% per year for a decade. The low capital costs and high
availability of CCGTs also make them highly desirable to
power station operators. Gregory and Rogner (1998) estimate
that maximum efficiencies of 71 to 73% are achievable within
a reasonable period (on a lower heating basis; around 65 to
68% on a higher heating basis).
CCGTs can also be used with more difficult fuels, such as coal
and biomass, by adding a gasifier to the front end to form an
integrated gasification combined cycle (IGCC) power station.
The gases need to be hot cleaned prior to combustion to avoid
energy losses and this is one of the key areas of development.
The added benefit is that coal flue gas desulfurization (FGD)
becomes unnecessary as sulfur is removed before the
combustion stage. In addition to FGD and IGCC, fluidized bed
combustion (FBC) technology facilitates sulfur abatement
(adding limestone during combustion to retain sulfur) and