In a world of increased awareness of the finite nature of fossil fuel resources, and of the consequences of global warming, we need an absolute benchmark to assess performance in energy utilization.

The first law of thermodynamics allows us to conduct energy balances, but by itself, it is insufficient - and even misleading in attempts to assess energy efficiency.

The second law of thermodynamics has been recognized for over 170 years since Carnot's insights regarding the limitations in converting heat into work in so-called power cycles or heat engines.

Despite this elapsed time, and perhaps because of the way thermodynamics is often taught, the appreciation of the importance of the Second Law and its practical use is not yet very widespread - even amongst practising professional engineers.

Exergy is one of several alternative terms used to denote absolute value of energy or the maximum theoretical energy (as shaft work) that can be extracted from a process stream - within a given environment.