From Thermodynamics to Economics and Ecology - Thanatia: The Destiny of the Earth's Mineral Resources - page 74

formalis” (i.e. the underlying idea of any production process) perhaps represents
society's enjoyment of life and ultimately its survival (Georgescu-Roegen, 1971).
Thus, the rearranged exergy balance now becomes:
Ex. Resources(F) - Ex. Products(P) = Ex. Wastes(R) + Irreversibilities(I) > 0
And the process e ciency is defined as:
E ciency = Ex. Product / Ex. Resources
Its inverse value is the unit exergy consumption:
Unit Ex. Consumption = Ex. Resources / Ex. Product
In a similar way, the e ciency for a waste reduction process is defined as:
Eff. = Ex. reduction of Wastes/ Ex. additional Resources to dispose of wastes
An ideal thermodynamic process would be that of zero irreversibilities, or in
other words, the unit exergy consumption of the product would be equal to one.
However, as experience demonstrates irreversibilities are never zero and the true
amount of exergy required in real processes per unit of exergy of the product is
what matters. This is described in the next section.
3.3.2 The exergy cost
3.3.2.1 Conceptual meaning
Only in a thermo-utopian world, could a person be forgiven in thinking that all
processes are reversible, i.e., they should go infinitesimally slow enough to reach
equilibrium and not subject to either friction or dissipative effects. In such case,
no additional exergy is destroyed and the manufacturing cost simply reflects its
minimum thermodynamic cost (exergy).
Friction and dissipation are required for life. By focusing on everyday processes,
one becomes steadily aware of the need for light with which to see or friction in
order to move. The conversion of electricity into an illuminating flux and in turn
into heat is a completely irreversible process. The same with friction, without which
most humans could not competently walk upright. The Earth's habitable condition
requires the constant and sacrificial destruction of solar exergy radiation. Life is
after all, a continuous irreversible process with death being the absence of that same
irreversibility.
Biological processes are closer to reversibility than manmade systems. The at-
mospheric fixation of CO 2 through the chlorophyll function of plants, for instance,
takes place at ambient temperature using only sunlight (this energy is of course at
very low density per surface unit). Yet in contrast, for Man to reduce CO 2 into pure
carbon or undertake hydrocarbon synthesis, a very complex and energy intensive
technology is required. Another key example of manmade versus natural e ciency
is the ingenious fixation of atmospheric nitrogen by leguminous plants. When Man