Environmental Engineering Reference
In-Depth Information
10.1 Energy Cost of Energy: Net Gains
Given the variety of fuels and their diverse extraction,
processing, and transportation modes as well as the range
of options for hydro, nuclear, wind, or solar powered
electricity generation, it is impossible to offer any gener-
ally valid energy costs of individual energies. Moreover,
EROI completely ignores the differences in the quality
of delivered energy (flexibility, convenience, portability,
cleanliness at the point of use) or considers them only in
terms of retail prices. And the quotient does not inform
about the pace of exhausting finite resources in contrast
to harnessing renewable flows. As a result, net energy
analysis is an ill-defined endeavor whose outcomes are
far from clear-cut and whose relative popularity during
the late 1970s and the early 1980s (Hannon 1981; Hall,
Cleveland, and Kaufmann 1986) rapidly ebbed after the
mid-1980s. This is not to say that the approach is not
heuristically valuable and that it should not be used as a
part of broader, more revealing appraisals of the compar-
ative merits of various energy resources and uses.
In a detailed account of capital equipment needed for
an underground mine with annual capacity of 1.4 Mt and
longwall extraction, and assuming liberally 100 GJ of
embodied energy per tonne of machinery, Duda and
Hemingway (1976) implied an investment of about 260
TJ/Mt of mine capacity and an electricity requirement of
about 45 TJ/Mt. Even if the total capital investment
were doubled, the energy cost during 30 years of opera-
tion would be about 1.9 PJ compared to at least 660 PJ
of coal (assuming 22 GJ/t), implying a net energy ratio
of 0.997 and EROI of 333. Sidney, Hemingway, and
Berkshire (1976) reported about 2250 t of equipment
needed per 1 Mt of annual capacity in a 4.4 Mt/a surface
mine, and annual operating needs per 1 Mt of 51 TJ of
electricity and 9 TJ of fuel. After doubling the capital
cost over 30 years, these rates translate to lifetime energy
costs of 2.3 PJ compared to 600 PJ of extracted fuel,
even for a lower-quality coal at 20 GJ/t, and imply
EROI of 250.
Similarly, other U.S. and British analyses (Chapman,
Leach, and Slesser 1974; Hayes 1976; Boustead and
Hancock 1979) showed coal-mining expenditures rang-
ing from less than 100 kJ/kg in surface mining of thick
high-quality seams to about 4 MJ/kg for underground
extraction of thin seams, values translating to delivered
net energy as high as 0.9975 (EROI 400), typically
about 0.97 (EROI 33), and no lower than about 0.83
(EROI
<
6). Cleveland (2005) put the typical EROI of
U.S. coal extraction at 100 in 1950 and at 80 in 2000.
Data on sectoral energy use prorate to about 140 kJ/kg
of coal, implying a net energy ratio of at least 0.993
(for coal with just 21 MJ/kg) and EROI of no less than
140. Secondary coal-based fuels will obviously cost more,
with delivered energy fractions ranging between 0.70
and 0.88 (EROI 3.3-8.3) for coke and between
0.65 and 0.81 (EROI 2.2-5.3) for manufactured gas.
Energy invested during the 1930s and 1940s in the
discovery of the largest Middle Eastern oil fields was ex-
traordinarily low, on the order of 1 MJ/t, or 0.0025% of
hydrocarbons in place, and the subsequent production
cost from these huge reservoirs (@0.5-5 GJ/t) yielded
wellhead EROI as high as 10
3
-10
4
. Chapman and
Hemming's (1976) calculations for two North Sea oil
fields, Auk and Forties, showed net energy requirements,
respectively, of about 840 MJ/t and 230 MJ/t, 2-3 OM
above the lowest Middle Eastern needs. However, even
in these demanding cases, the overall energy costs of oil
production were repaid in oil in less than three months.
Similarly, my calculations show that the record-breaking
Ursa platform, built in more-than-1100-m-deep waters
