Synthesis and Optimal Operation of Smart Microgrids Serving a Cluster of Buildings in a Campus with Centralized and Distributed Hybrid Renewable Energy Systems

Design and optimal operation of energy systems serving clusters of buildings interconnected by energy microgrids is a great scientific opportunity for the engineering community, with many interdisciplinary aspects involved. High energy efficiency can be reached by appropriate and cost-effective integration of locally-available renewable energy sources, centralized polygeneration systems and distributed control of back-up generators and storages. The lack of established design criteria for these hybrid systems and of comprehensive simulation tools are slowing down the spreading of such concept for sustainable urban development. In the paper, the optimization problem is tackled in terms of simulation-based design of the energy system for a typical year of operation. The methodology has been applied to a Campus in Trieste, Italy. We modelled every subsystem involved in energy balances: electrical and thermal energy generators, electrical microgrid, micro-district heating network, wind turbine, photovoltaic and solar thermal panels, thermal storages, heat pumps and chillers, boilers, building envelope thermal response and building heating, cooling, domestic hot water and electrical uses. The level of modelling is sufficiently detailed to consider the main physical and technical aspects involved, but, at the same time, is sufficiently simplified to preserve computational efficiency for the optimization routine. The subsystems are properly coupled, to form a single set of equations, allowing to perform an annual simulation of the whole energy system. The size of the combined heat and power plant has been optimized. We have also found the optimal modulation profile of energy generators (centralized cogeneration unit and distributed heat pumps and boilers) by means of a greedy algorithm. The solution with minimal annual costs is discussed, as well as the capability of heat pumps of conveniently and dynamically shifting thermal loads into electrical loads. This optimal configuration is compared to a less flexible design alternative, not employing distributed heat pumps and having 20% higher annual costs.