Geology Reference
In-Depth Information
2.6.3.1 Embodied energy
Embodied energy is the energy needed to manufacture a product or provide a ser-
vice along an entire product life-cycle. It was first proposed by Hannon (1973) and
has since been widely used by ecological economists. Originally, the concept was
obtained as an outcome of the Input-Output theory (Leontief, 1951), in which every
member of an ecosystem depends on each other and is described in terms of the di-
rect and indirect energy needed to maintain the whole. Currently, embodied energy
is an accounting methodology fully incorporated into the majority of commercial
Life Cycle Assessments (LCA) software
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. The weakness of the methodology is the
lack of accounting rules for allocating energy inputs among co-products, by-products
and wastes, resulting in a wide range of subjective embodied energy values for any
given material. There is also no international consensus because it lacks thermody-
namic fundamentals. However, for many aggregated systems, the embodied energy
analysis provides valuable results.
2.6.3.2 Emergy
H.T. Odum was a recognised biologist that centred his work on environmental
accounting and ecosystems behaviour. He proposed Emergy as a concept to express
the amount of direct and indirect solar energy needed to produce any product
or service. Emergy analysis has been applied to evaluate systems as complex as
ecosystem services and questions relating to policy, agriculture, urban planning and
urban development (Odum, 1976, 1983, 1995b).
The unit of measure is the solar emergy joule (sej) or “emjoules”. To derive the
solar emergy of a resource or commodity, it is necessary to trace back through all
the resources, including energy, that were used to produce it and express them in
the equivalent amount of solar energy that went into their production (Brown and
Herendeen, 1996). The solar emergy per unit product or output flow is called “solar
transformity”, with units of seJ=J. Solar transformities have to be obtained for
each commodity individually. Subsequently, they cannot be considered universal,
as the processes involved in the formation of the commodities differ, depending on
the period of time and place considered.
One of its fundamental concepts is the maximum empower principle. It is stated
as “systems that will prevail in competition with others, develop the most useful
work with inflowing emergy sources by reinforcing productive processes and over-
coming limitations through system organisation”.
Ultimately, its proponents claim that emergy is in fact exergy (see Sec. 3.2.3
for more details) and emergy analysis can therefore be used to account for a given
product in one type of energy quality or another, thus permitting a move away from
“emjoules”. But there are significant dissimilarities: a) the balance of emergy for
a given system is not the irreversibility produced and b) the way the methodology
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See for instance the pioneering work of Boustead and Hancock (1979).
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