Increased efficiency of conversion
While efficient combined cycle gas turbine currently represent state-of-the art of power generation with
natural gas, there still are a range of technologies used for existing and new plants using coal, which
exhibit diverse energy efficiency – and CO2 emissions – performances.
Electricity generation accounted for 39 per cent of global carbon emissions in 2000. Baseline scenarios
anticipate emissions of 3.5 GtC and 4 GtC for 2010 and 2020, respectively. The IPCC sets the potential for
reductions at 350-700 MtC by 2020. Focusing on OECD Member countries, IEA’s “Alternative Policy
Case” predicts possible CO2 emission reductions below reference scenarios of 4 per cent in 2010, 15 per
cent in 2020, and 25 per cent in 2030 in these countries.
Prospects might be brighter in developing countries, where large investments in the power sector will be
needed. Over the next twenty years,
China and India alone are expected to build up to 500 and 200 GW
respectively of new power generation capacity, of which at least 350 and 125 GW will be new coal plants.
These new plants will partially replace older ones, thus increasing the average energy efficiency of the
sector. However, if new capacities were of an advanced super-critical design rather than the classical subcritical design, their efficiency would be increased by a further seven percentage points and their CO2
emissions reduced by about 15 per cent compared to current projections. Here, the critical issue may not be
costs, but technology transfer, as even with low coal prices, subsequent fuel savings would pay for the
incremental cost of investing in the most efficient technology.
Further CO2 reductions and energy efficiency increases will be possible using more advanced concepts
such as “ultra-ultra” super-critical plants, fluidised bed combustion processes. Integrated gasification
combined cycle power generation may offer longer term prospects, although existing pilot plants have thus
far failed to demonstrate high energy efficiencies.
Another important way to raise the efficiency of energy use is simply to use the heat that cannot be
converted into electricity in “combined heat and power” (CHP) systems
. Electrification has in general
6
Gas hydrates may contain three orders of magnitude more methane than exists in today’s
atmosphere. Because hydrate breakdown, causing release to the atmosphere, can be related to global
temperature increases, gas hydrates may play an even more important role in global climate change.
COM/ENV/EPOC/IEA/SLT(2003)4
38
many advantages, including for raising efficiency in end-use processes. However, burning fossil fuels to
create heat, converting that heat into electricity, and then using this electricity to produce heat for end-users
is not a very efficient way of doing things. Thus, only combined heat and power raises efficiency higher
than approximately 50% (in single cycle machines) or 60% (in combined cycles). It has been estimated that
CHP might reduce CO2 emissions by 20 to 40% - depending on the assumptions made on the reference
case. Stationary fuel cells could also provide distributed combined heat-and-power.
More than 80% of current CHP capacity is used in large industrial applications, mostly in four sectors:
paper, chemicals, petroleum refining, and food processing. Further CHP expansion in industry and
commercial and residential sectors would be facilitated by more distributed energy systems, where power
generation is closer to end-users. While recent IEA analyses finds that distributed generation is not yet
ready to replace existing systems, there are changes to regulations and market rules which could promote a
larger role (IEA, 2002e).
