Environmental Engineering Reference
In-Depth Information
scarcities, and only demand can accomplish their effective
valuation. Market-driven innovation reduces embodied
energy, and the resulting energy savings may greatly
surpass any gains brought by efforts aimed solely at mini-
mizing energy inputs. The demand for speed and capac-
ity in electronic computing has been accompanied by
dramatic reductions of both embodied and operating
energies; the deployment of highly efficient turbofans
was driven by the need to accommodate more passengers
on longer flights.
Net energy assessments encounter their most frustrat-
ing problems in the choice of boundaries and the treat-
ment of mental labor (see chapter 10). Decisions about
where to stop the analysis have no acceptable universal
solutions. Misleading results are especially likely if the
goal of the exercise is the energy-based valuation of all
cascading consequences. Energy flows may have a fractal
structure, and hence there may be no finite net energy
cost. No less vexing is the necessity of converting to a
common denominator. Excluding sunlight from an all-
encompassing net energy analysis is indefensible; sunlight
should count, but to count it coherently is daunting. In
Odum's accounting, using more emergy does more real
work and leads to a higher standard of life. But does the
fact that items with longer turnover times necessarily
have higher transformities imply that we should value oak
trees up to 10
7
more than bacteria? The biosphere can
prosper without oaks but not without bacteria. Why,
then, should oaks be valued so much more than bacteria?
And how can we express geotectonic processes (whose
priming has nothing to do with solar radiation) in sej?
Similarly, how should we estimate the solar energy
embodied in fossil fuels? Should we include just the solar
radiation that energized the synthesis of original phyto-
mass, or the radiation that energized erosion and sedi-
mentation that buried and transformed the phytomass?
What portions of those flows are attributable to fuel for-
mation, and how can the inputs of tectonic (nonsolar)
energies on fuel formation be included? Incredibly,
Odum favored a single transformity for each of the three
main fossil fuels, a gross distortion of reality because some
of them required 10
3
years to form and others 10
8
years
to form. Single sej values are thus inconsistent with
the technique's key premise of quality varying with
embodied energy. In any case, in real world quality is de-
termined not by the age of the original phytomass but by
the presence of sulfur, ash, and moisture in the fuel (see
sections 8.1 and 8.2), and the market t value is strongly
affected by the mode of extraction and the cost of trans-
port, variables that have nothing to do with ancient solar
flux.
The main criticism of exergy is that it does not capture
such qualitative attributes as energy density, cleanliness,
ease of conversion, and relative environmental impacts.
For materials, exergy does not capture such qualitative
factors as tensile strength, heat and corrosion resistance,
ductility, and conductivity (Cleveland, Kaufmann, and
Stern 2000). In practical terms, actual calculation of
exergies in a national economy would be extremely chal-
lenging. In sum, the intent of energy-based valuations
may be laudable, but their execution must remain un-
satisfactory. Energy-based valuations have brought more
heat than light to our understanding of economic and
social values (Mirowski 1988). They have been subject
to a number of fundamental methodological problems
typical of the social sciences (Reaven 1984).
True understanding calls for a multidimensional
approach. We should definitely pay attention to em-
bodied and net energy, but we must also realize that
even such a fundamental entity as energy (be it under
