172
Pathways
to
Sustainability:
The issue of energy quality is important because it introduces
a notion of efficiency
Assessing
Our
Progress
than it was before)” (Brooks 1981,269). The idea of calculating Second Law
that is not captured in the First Law efficiency described previously. It recognizes that techni-
efficiency was first proposed in 1974 by the American Physical Society and the
cal and economic efficiencies can be gained by matching end uses with an appropriate quality of energy. This aspect of efficiency has come to be known as “Second Law” efficiency because of its link to the Second Law of Thermodynamics. Formally stated, this law is:
International Federation of Institutes of Advanced Study. They defined Second Law efficiency as the ratio of the least available work (energy) that could have done the job to the actual available work (energy) that was used to do the job (Torrie 1977,6-12). In principle, monitoring Second Law
A natural process that starts in one equilibrium
state and ends in another will
go in the direction (or disorder) to increase.
that causes the entropy
of the system plus environment (Modified from Halliday
and Resuick 1966, 638-642)
In rough terms and applied to energy production, it can be more simply expressed as “the quality of energy is always diminished (that is, becomes less valuable to us afterwards
efficiency is as important to assessing progress toward sustainability as monitoring First Law efficiency. In reality, energy accounting systems are entirely geared to energy quantity and not quality. This is a serious limitation given that the largest gains in efficiency that remain are likely to be realized through (I) matching energy end uses to energy forms of appropriate quality; and (2) finding ways of doing things