The target of the paper is to bring an argument on behalf of the use of exergy in the analysis of the operating and optimization of complex energetic systems. For a system with more than one product, the proper cost assessment for each one of them requires, besides the global economic balance, some supplementary assumptions. The exergetic equivalence succeeds in giving the true value of utilization for different types of energy products; the cost assessment based on exergetic analysis is close to reality. For a single product system the optimization procedure based on the first law of thermodynamics only, implies complicated calculus. The use of the marginal cost concept in the optimization analysis based on Lagrange’s multipliers gives the direction to follow for the optimum solution field search.

Keywords: Exergetic analysis, Thermoeconomics, Optimization, Marginal cost