Environmental Engineering Reference
In-Depth Information
for atmospheric concentration to stabilize at 550ppm, thereby reducing the risk of cata-
strophic climate change.
1.2.7 Possible Solutions and Sustainability
Fundamental choices will have to be made in the years ahead. Societies are presently depen-
dent on high and growing fossil fuel consumption. The possibility of weaning people from
this dependence over a short timescale is completely unrealistic. The general shift in fossil
fuels over the last two decades for both electricity generation and heating has been towards
increased use of gas in place of coal, and to a lesser extent oil. This has helped to limit the
growth in CO
2
emissions as gas combustion releases less CO
2
per unit of energy than coal.
Political events, however, have generated anxiety in the EU and elsewhere in relation to
increased dependence on this particular fuel.
A possible alternative path is to revert to dependence on coal. This resource is abundantly
available in many developed counties including the US, Australia, many EU countries,
Canada, Russia and in developing countries such as China, South Africa and Turkey. Recent
developments in CO
2
capture or 'sequestration' for fossil fuels, discussed later in this chapter,
give some hope that this source may be made more acceptable environmentally.
A number of potentially carbon neutral sources exist: these include nuclear fi ssion (and
possibly fusion in the far future) and all sources that derive directly or indirectly from the
sun, namely biomass, wind, solar (thermal and photovoltaic), hydroelectric and marine. Geo-
thermal and tidal energy are also carbon neutral and often regarded as renewable on the
grounds that the sources are so huge as to be virtually inexhaustible. In Chapter 2, the
characteristics of all these conventional and emerging technologies are discussed in some
detail.
Finally, but no less important, other approaches essential in the move towards sustainability
are a reduction in energy needs and improvements in the effi ciency of energy use. The latter
includes more effi cient electricity generation. Although not the main focus of this topic, these
topics are briefl y discussed in this chapter.
The planet's reserves of fossil fuels and minerals are of course fi nite, and thus the exploita-
tion of coal, oil, gas and uranium are not sustainable in the longer term. Fortunately, renew-
able energy (RE), being derived from naturally occurring energy fl ows, is inexhaustible and
has no long term detrimental effect on the environment. As such it will in time become the
basis of the energy supply system, and probably the sole means by which electricity is
generated.
1.3 Generating Electricity
1.3.1 Conversion from other Energy Forms - the Importance of Effi ciency
Figure 1.8 shows the ways in which various types of energy can be converted into electricity.
At present, the path generating the bulk of electricity worldwide is shown by the bold lines
that lead through combustion from chemical to thermal, from thermal to mechanical and
fi nally to electrical power conversion. The bottleneck of this path is the limited thermody-
namic effi ciency determined by the Carnot cycle. Older thermal generating stations have
