Thesis title: Managing Energy Flexibility across the power distribution network
The fundamental role of energy flexibility in the modern electricity distribution networks was deeply highlighted in this thesis, pointing out the widespread interest in the topic of the European community. The distribution network of ASM Terni was the real trial site to validate the flexibility optimization algorithms proposed in this work. ASM headquarter enabled the possibility to test a model and an optimization algorithm of the energy district which combine a Fuel Cell Electric Vehicle fleet, internal generation, hydrogen system and facilities with electrical loads. The multi-parametric analysis is particularly significant for districts similar to the one considered, namely, an energy district supporting a Fuel Cell Electric Vehicle fleet providing service to an average city with a city centre, industrial areas and countryside.
With respect to the electric mobility, the hosting capacity evaluation method proposed in the thesis was identified as a first study to allow the flexibility assessment related to the possibility of re-scheduling the charging sessions. The electric mobility hosting capacity evaluation applied to Terni distribution network highlights that currently the subnetwork supplying the city center has a low hosting capacity. Without considering grid reinforcements or the possibility to inhibit charging stations during operation, the number of charging stations that can be installed in the subnetwork is 126, whereas inhibition of charging stations and grid reinforcements could allow the installation of 314 and 502 charging stations, respectively. The proposed evaluation procedures seem adequate to be exploited by Distribution System Operators, since they only require the model of the distribution network and load profiles recorded at each secondary substation.
Another flexibility source investigated in the thesis consists of the promising hydrogen based technologies. The sizing and location of systems consisting of fuel cells, electrolyser and hydrogen storage was analysed, showing the possibility of consuming 38.7% of the energy surplus locally in the case of an entire medium voltage subnetwork of Terni distribution network; by means of the installation of these systems, the reverse power flows are reduced by 14.8%.
Moving on the National energy value chain, a static and dynamic analysis of 100% renewable power grids was proposed. In particular, a model for the sizing of power production plants and storage systems in a 100% renewable electricity system was investigated, with the aim of minimising the annual aggregate cost of electricity generation. The dynamic analysis focused on simulations in the MatDyn environment for the evaluation of the frequency response of a 100% renewable network. The 112-bus Sardinia islanded power system was analysed in a scenario of a fully renewable independent power system. The lack of synchronous generators in the grid, due to the conventional power plants shutdowns, requires higher performances from renewable power plants in terms of synchronization and inertial response. The DFIGs, together with the available hydropower plant, were selected as the more suitable renewable production systems to guarantee frequency stability by an appropriately enhanced response.