Environmental Engineering Reference
In-Depth Information
willing to incur considerable losses in order to produce
energy whose qualities surpass those of the primary fuels
used in its generation.
Minimum returns of fission-based generation can be
estimated by assuming that the highly energy-intensive
production of enriched uranium fuel in gaseous diffusion
plants claims 4%-5% of the station's gross annual output
during 25 years of operation, and that construction costs
may be equivalent to 6% of produced electricity (Chap-
man, Leach, and Slesser 1974). With 9%-10% taken by
the plant's consumption and by distribution losses, nu-
clear stations would have EROI as low as 5 (excluding
the energy content of the charged fuel). Meier and Kul-
cinski (2002) use an average of about 15. EROI for
CANDU reactors using natural uranium (no need for
energy-intensive enrichment) was put at 16; several other
published estimates of the energy payback ratio for
nuclear generation range between 20 and 60 and go
(unrealistically) as high as 100 (Gagnon, B´langer, and
Uchiyama 2002; WNA 2006a). But because there is no
way to include the ultimate energy cost of decommis-
sioning and long-term disposal (10
4
years) of radioactive
wastes, any arguments about the net energy of fission
generation rest on grossly incomplete assumptions.
A different accounting challenge is presented by hy-
droelectric generation, where the only simple cases are
presented by projects dedicated solely to electricity gen-
eration. In all other cases, calculations of energy costs
are complicated by the multipurpose function of dams
and reservoirs. Is it appropriate to charge the construc-
tion cost (including often high costs of population
relocation) only against electricity generation when a res-
ervoir is also used for flood control, irrigation, drinking
water, or recreation? Further complications arise from
different longevities of hydro projects (heavy silting may
fill some reservoirs in less than 50 years, while reservoirs
in wooded areas last for centuries), the necessity for ex-
pensive (often DC) high-voltage transmission links to
distant load centers, and the fact that there is no accepted
procedure to account for the renewability of hydrogener-
ation. Published ratios range widely for stations with res-
ervoirs (EROI 50-260) and for run-of-river projects
(EROI
<
50-
>
260); those for specific Hydro-Qu
´
bec
projects assessed over a period of 100 years are, respec-
tively, 205 and 267 (Gagnon, B
´
langer, and Uchiyama
2002).
Among the techniques of renewable electricity genera-
tion, the published EROI estimates (3-80) of wind
turbines have ranged too much to offer any representa-
tive values. Combustion of sawmill wastes is definitely
quite rewarding (EROI
>
25). The lowest values are,
expectedly, associated with electricity generated by burn-
ing wood from intensively cultivated tree plantations
(EROI
<
5 not counting conversion losses, and @1.5
when including the energy content of wood) and from
biomass conversions to liquid fuel. There have been
many studies of the energy costs of corn-based ethanol
fermentation with results ranging from net energy loss
(Pimentel 1991, 2003; Keeney and DeLuca 1992) to
substantial energy gains. Results of the final out-
come depend on the inclusion of energy credits for
by-products. Shapouri, Duffield, and Wang (2004)
calculated a barely positive EROI of 1.06, but energy
credits for by-products (including distillers grain and
corn gluten meal) raise it to 1.67. A similar analysis by
Kim and Dale (2002) found a final EROI of 1.56.
In contrast, Pimentel's studies (accounting also for en-
ergy cost of field machinery and irrigation and assuming
lower by-product credits) kept confirming energy loss
for the entire enterprise. The latest one (Pimentel 2003)
