A model for energy systems optimization based on energy hubs theory

The present energetic and environmental situation requires a deep thinking about the strategies and the technologies used to face the energy needs, particularly in countries like Italy, which depends on the foreign supplies (more than 85% of the energy demand) and mainly exploits non-renewable resources (more than 90% of the total consumption). In these last years, it has become clear that in order to optimize the use of resources and fulfil users requirement, the analysis not only of single plants, but also of the integrated systems among producers and users must be performed, considering transmission and emissions restrictions, accumulators presence, conversion between different forms of energy. This is very important in the present energetic scenario, particularly for small co-generative distributed plants, which are often fed by not predictable renewable fonts and/or whose production is strictly connected to the users load. This paper presents a model based on the theory of energy hubs for the simulation of systems of conversion plants, infrastructures and users, connected among them and with the environment by vectors networks (electric energy, hot and cold fluids, fuels). The model permits to exploit the synergy among different energy vectors, considering their characteristics, as energy density, cost, simplicity of accumulation or transmission, availability, emissions. So, for each system it permits to study different solutions combining in different ways the fuels, the energy flows among plants, the load of each plant, the energy outputs. In this way, for each set of external variables (requirement of users, tariffs of purchase and sale of energy vectors, renewable source availability, ..) the user can choose the best solution in terms of energy consumption, overall cost and/or environmental impact. An example of application of the model to the tri-generative system of a big hospital will be presented.