Criteria for the decomposition of energy systems in local/global optimizations

The decomposition of an energy system into subsystems of reduced complexity, to be optimized separately, but in a way compatible with the optimum of the global system, has been recognized as a viable solution to the problem of the design optimization of highly integrated, complex energy systems. Iterative Local/Global Optimization (ILGO) and its dynamic extension (DILGO) permit the decomposition of the global problem into smaller subproblems to be optimized separately, guaranteeing in the process that the subproblem optima eventually converge after a small number of iterations to or near to the optimum of the original global problem. The aim of this paper is to analyze the criteria for energy system decomposition, in particular with regard to the formulation of the separate subproblems and to the imposition of the constraints that affect the coupling of two or more subsystems. Three general decomposition criteria are identified and discussed with simple examples to let the mathematical formulation be analyzed critically.