Environmental Engineering Reference
In-Depth Information
in rolled steel, aluminum engine block, or a plastic
bumper, the analysis has to move to the next level,
embracing the inputs needed to produces those compo-
nents. Further extension includes the energies needed to
produce and distribute fuels and electricity used at differ-
ent stages of the process, and it could also approximate
the energy costs of equipment used in manufacturing or
assembly as well as in the production of key components.
Boundary dilemmas that go beyond energy analysis are
well illustrated by trying to decide between a cotton and
a polyester shirt. Process energy analysis shows cotton
costing three times as much energy as polyester (Van
Winkle et al. 1978). But this advantage is lost in the
wearing; the LCA (including washing, drying, and iron-
ing) puts the cost of the polyester shirt about 35% lower.
But cotton cultivation also yields cottonseed oil, and
credits for its energy make a cotton shirt only marginally
more costly than the polyester one. The small remaining
difference may easily be outweighed by the superior
wearing qualities of cotton and by its renewability. Yet
we may turn once again and note that erosion in a Texas
cotton field removes annually about three times as much
topsoil as is compatible with sustainable farming; that in
Egypt cotton displaces food crops and leaves the country
dependent on food imports; that the irrigation of the
cotton crop in arid areas contributes heavily to severe
soil salinization; and that residues from high doses of her-
bicides pollute the local environment.
Detailed production sequences and itemized inputs
are available for many products, but other cases call for
ingenuity and perseverance. Most analyses encounter
missing information and require many unavoidable
approximations, especially regarding the average lifetime
of machines. Discrepancies
identical products are due to different analytical bounda-
ries, to studies of different techniques producing the
same commodity, to comparisons of identical processes
in plants of different ages and maintenance practices,
and to the inclusion of marketable by-products. Net en-
ergy analysis, the study of energy required to produce
energy, has its own challenges. Herendeen (1998)
thought that it is conceptually fatal, particularly when
several types of energy have to be considered. Its out-
come is usually expressed as the quotient of marketed en-
ergy (output) and the energy needed for its production
(extraction, processing, or transportation input), and the
measure has become known as energy return on invest-
ment (Hall, Cleveland, and Kaufmann 1986).
EROI (more correctly it should be EROIE, energy re-
turn on invested energy), or simply net energy of primary
energy supplies, must be substantially greater than 1, but
in some cases it has been unclear whether the net rate is
above, near, or below the breakeven point. Perhaps the
best-known case of this uncertainty is the net energy re-
turn of fuel alcohol (ethanol), fermented from corn (see
section 10.1). Studies of embodied energy identified en-
ergy losses and opportunities for improved conversion
efficiencies and reduced energy inputs, and demonstrated
energy's critical role in modern economies, which is
often obscured by distorted pricing. But why stop with
energy? Why not find the embodied content of other
critical materials needed to produce goods and services,
above all, water and land? More important, studies of
embodied energy have not (contrary to some overenthu-
siastic opinions) displaced standard economic analyses
because neither individuals nor corporations base their
decisions on the minimization or optimization of energy
costs.
in values
for apparently
