Environmental Engineering Reference
In-Depth Information
widely re-proposed and discussed in recent years [
11
-
14
], and applied to world oil
production for incoming years. The results, in spite the above pointed out diffi-
culties of this type of prediction, converge towards the conclusion that oil
worldwide production peak should be reached around 2020 [
15
-
17
]. Without
considering here neither the apocalyptic scenarios of oil peak theory upholders,
nor the skepticism of its deniers, it is possible to observe that there is a virtual
agreement among geologists that world production of conventional oil will peak at
some point in a not too distant future. On the other hand, considering the other
fossil sources, natural gas (only marginally used in the transportation sector) will
see its production peak some years later than oil, while for coal (mainly used
worldwide for electric energy generation) this will occur some decades later.
Natural gas is directly usable as fuel for road vehicles (see
Sect. 1.2
), while coal
should be before converted to syngas (CO ? H
2
) and subsequently to liquid
hydrocarbons by the Fischer-Tropsch process [
18
]; however, these solutions can
give benefits in terms of mitigation of the current dependence of transportation
sector on petroleum, but do not represent a solution for the problem of CO
2
emissions (see
Sect. 1.3
). On the other hand, the use of biofuels for vehicles could
help to reduce the global CO
2
emissions, but issues regarding efficiency of the
production process limit them at a niche sector (see
Sects. 1.2
and
1.3
). These
considerations, together with the well-ascertained fact that energy and mobility
demand will only grow over time, and the diffused awareness about climate
change problem, appear as sufficient motivations to stimulate policy makers and
governments to plan effective implementation of alternative non-fossil energy
resources. The link between the development of different energy resources and the
decoupling of transports from petroleum consists in the possibility to exploit in
this field energy carriers alternatives to conventional fossil fuels, i.e. electricity and
hydrogen. This can be realized by a widespread diffusion of electric vehicles,
which could adopt two different solutions regarding the supply of energy to
the electric drive (see
Chap. 5
): electric energy storage systems (battery electric
vehicles, BEV) or electric energy generation systems, such as hydrogen
fuel cells, in hybrid configuration with batteries (hydrogen fuel cell electric
vehicles, HFCEV).
The interest of using hydrogen as fuel in the transportation sector is based not
only on its very high specific energy (see
Sect. 1.2
), but above all on its unique
characteristic of not emitting any carbonaceous emission during its utilization for
energy production, being water its only oxidation product. However, like elec-
tricity, it is not an energy source, but rather an energy carrier. In fact, although
hydrogen is the most abundant chemical element in the universe (about 80%, the
remainder being mostly helium) and the third most diffused element on earth after
oxygen and silicon, it is not significantly present on our planet in the free state
directly usable for energy production (diatomic gaseous molecule), but only in its
compounds. Therefore, hydrogen has to be generated from primary sources (water
and fossil hydrocarbons can be considered the most commune hydrogen sources),
and this conversion can be performed by several processes (see
Sect. 2.1
).
However, it appears obvious that if the fundamental advantage of hydrogen
