Optimization of an industrial area Energy Supply Systems with distrubuted cogeneration and solar district heating

The paper presents the optimization of an energy supply system for an Italian industrial area. The system is mainly composed of a district heating network (DHN), of a thermal solar plant with seasonal heat storage, of a set of combined heat and power units (CHP) and of additional thermal energy supply machines. The thermal vector can be produced by solar thermal modules, by biogas/biomass cogeneration systems, by fossil-fuel cogenerators or by conventional boilers. The optimization algorithm, based on a Mixed Integer Linear Programming (MILP) model, has to determine the optimal structure of the energy system and the size of the components (solar plant area, heat storage volume, machines sizes, etc.). The model allows to calculate the economical and environmental benefits of the solar thermal plant compared to the cogenerative production, as well as the share of the thermal demand covered by renewable energies. The aim of the paper is to identify the economical conditions that make the usage of the renewable energy sources effective and how these conditions affect the optimal energy system configuration and the optimal input energy mix required to satisfy the users energy demands. The average cost of the heat produced for the users have been evaluated for different optimal configurations, and it emerges that the solution including some cogenerators located in strategic production units, the district heating network, the seasonal heat storage and the solar plant of appropriate size allow achieving the lowest cost of the heat. Thus, the integrated solution turns out to be the best both from the economical and environmental point of view.