Environmental Engineering Reference
In-Depth Information
Table 1.3 Estimations of
energy return on investment
(EROI) ratios for different
energy processes
Fuel supply technology
EROI
Oil and gas (wellhead) 1940s
[100
Oil and gas (wellhead) 1970s
8
Coal (mine mouth) (1950s)
80
Coal (mine mouth) (1970s)
30
Ethanol (sugarcane)
0.8-1.7
Coal to electricity
9.0
Hydropower to electricity
11.2
Nuclear to electricity (light water reactors)
4.0
Solar Photovoltaic to electricity
1.7-10
Adapted from reference [
39
]
can be introduced by extra-market interventions, such as governmental incentives in
favor of a particular technology [
38
]. For this reason, in spite of uncertainties about
the LCA evaluations, the EROI method appears more reliable than money-based
assessments, and data ranges present in literature are sufficient for an useful
comparison between different energy supply processes. Some estimates based on
reference [
39
] are reported in Table
1.3
, where any value of EROI\1 implies a net
loss of energy, that is more energy has been consumed with respect to that produced
during the life cycle of the plant, while the higher EROI is, the more convenient the
production process results in energetic terms. It can be noticed that EROI for oil and
gas was very high ([100) before 1970, after then it rapidly decreased due to the
exhausting of the largest and cheapest wells. EROI of coal for electricity production
is still quite high (about 9), but this technology produces the highest CO
2
emissions
at parity of electric energy produced. Among carbon-free resources the EROI of
nuclear power to electricity is lower than fossil resources and comparable to that of
solar photovoltaics (about 1.7-10).
The EROI approach suggests that, in spite of the limitations of new renewable
energy resources above considered, the significant potentialities not yet entirely
exploited offered by these alternative technologies should convince scientists and
politicians to make any possible effort aimed at their widespread diffusion, in
order to limit the future necessity to resort to fossil or nuclear sources. In parti-
cular, electricity produced by renewable resources can be used for decentralized
production of hydrogen, with a strong interaction between these two clean energy
carriers, which could be extended to the transportation sector.
1.2 Internal Combustion Engines and Their Impact
on Air Quality
Motor vehicles are a key factor affecting both economy and lifestyle of popula-
tions in rich countries, and are gaining the same role in emerging nations. Thus, the
growth in human mobility demand is expected to continue, intensifying the neg-
ative impact of transportation means on environment.
