Optimal operation planning of Distributed Energy Systems through multi-objective approach: a new sustainability-oriented pathway

The energy system is an essential part of nowadays society. The concept of “energy system” commonly refers to the energy-supply chain as the whole system consisting of the energy conversion devices as well as storage units from the energy resources to the final user demands. In the 1900’s, energy has been commonly provided by large generation power plants operating in a central location and transmitted to consumers via transmission and distribution networks. In a typical centralized energy system, a large number of end-users is located within a large area. A Distributed Energy System (DES) can be regarded as the opposite of a centralized energy system, where the term “distributed” illustrates how single energy conversion devices and storage units are integrated into the whole energy system. Therefore, a DES refers to an energy system, where energy is made available close to energy consumers, typically relying on a number of small-scale technologies. In recent years, developing DESs has attracted much interest, since these systems have been recognized as a sustainability-oriented alternative to conventional centralized energy systems. In general, sustainability means an equitable distribution of the limited resources and opportunities in the context of the economy, the society, and the environment, aiming at the well-being of everyone, now and in future, thereby guaranteeing that needs of future generations may be completely satisfied as happens today. One of the main benefits of DESs is the possibility to integrate different energy resources, including renewable ones, as well as to recover waste heat from power generation plants for thermal purposes. This benefit allows to enhance sustainability of the energy supply through a more efficient use of the energy resources as well as a reduced environmental impact, as compared with conventional energy supply systems. Through an appropriate planning, DESs may exhibit even better performances than a single polygeneration system, such as Combined Cooling Heating and Power systems or conventional energy supply systems. The optimal planning of DESs is not a trivial task, as integration of different types of energy resources and energy conversion devices as well as storage units may increase the complexity of the system. Moreover, generally different stakeholders participate in DESs development and management. Hence, objectives can be defined from different perspectives, such as the developers and operators of DESs, or the civil society, ideally represented by the regulator. Some of the DESs planning objectives are naturally conflicting. Consequently, there is not a single planning solution, which can satisfy all the stakeholders. For instance, society interest in sustainable energy supply systems, and with low environmental impacts, might conflict with the economic interest of the developers and operators of DESs. A multi-objective approach helps to identify compromise solutions, which benefit all the stakeholders. This thesis presents an original tool based on a mathematical programming approach, to attain the optimal operation planning of DESs through multi-objective criteria, by considering both short- and long-run priorities. Multi-objective optimization problems are formulated to find the optimized operation strategies of DESs in order to take into account short-run priorities characterized by the crucial economic factor, as well as long-run priorities in terms of sustainability. This latter is attained through exergy concepts as well as environmental impacts assessments