Flexibility of Electric Power Systems by Network Planning and Service Provision: Challenges for Energy Transition

In recent years, the electric power system is meeting a radical evolution due to the increasing penetration of Renewable Energy Sources (RESs). These have a relevant impact on most of the applications concerning the electrical network, such as the electricity markets, regulation services provision and the grid management and protection. However, the deep RESs deployment is the answer that countries all over the world are pursuing to fight climate change according to the Sustainable Development Goals (SDGs) adopted by the United Nations (UN). This evolution requires a great development of the network, that has to host a large quantity of new RESs, and the establishment of new strategies to deal with new challenges. More and more reserves for regulation services are pursued by units that couldn’t provide dispatching services until now, namely small-sized plants and RESs, but also load and storage systems. The demand has become increasingly more active since it has made possible a contribution to instability issues by varying their power profile for a certain amount of time without compromising the final user’s comfort, which means being flexible. As a result, a huge amount of new generation units and load units have started to provide dispatching services by participating to the electricity markets. This condition has led to the need of the improvement of the communication systems among all the actors in the process of power transmission alongside grid balancing, including the Transmission System Operator (TSO), the Distribution System Operators (DSOs), generation, load units and other data aggregators. The observability of the system is essential to forecast load and generation profiles in order to provide a suitable balancing service and to guarantee the reliability, safety and power quality of the electrical network through state estimation methods which are going to be widely used in modern systems. Observability is also important in making decisions for the planning of the network development by giving access to information about the grid operating conditions. Therefore it suggests how to focus the efforts to improve the electric power system performance according to the objectives established to reduce the impact of fossil fuels in the climate change. In sight of this, it can be concluded that the key to deal with climate change is a suitable coordination of such factors: the development of the network, the arrangement of flexibility resources and the communication systems improvement. During the Doctorate (Ph.D.), the author has worked on several research projects related to the topic of the evolution of the electric system. The project are listed in the Appendices. This thesis gathers the work done by underlining the importance of the three factors mentioned before in the context of the power system evolution. The developed applications will be presented as particular approaches that can be applied to a general power system and take place in one or more aspects of the ecological transition. In Chapter 1, the UN strategies to deal with climate change are introduced as well as the main consequences they led to and the new needs of the electric system are described. An introduction to regulation services and their purpose is given. In Chapter 2 the Italian context, as part of the European and Global plan to reduce emissions, is described. The main tools used by the Italian TSO to plan the network development are introduced and the study case of the network of Sicily is explained in the contest of the project ”Assessments of Battery Energy Storage Systems Potential in Improving the Working Condition of the Grid of Sicily”. As a continuation of this work, the method developed in the project ”Optimal Storage Allocation for Transmission Network Development Planning” is applied to the Sicilian network model and its possible contribution to network infrastructure planning is described. In Chapter 3 the impact that the installation of several RESs have on the grid stability is described. The consequent evolution process of the electricity market in order to cope with the increased need of regulation services is explained. In such context, pilot projects have been established by the TSO to encourage research of flexibility resources with reference to the projects concerning regulation service provision from loads and RESs. In Chapter 4, in project ”Flexibility Evaluation of an Aggregate of Thermal Load Units”, a definition of flexibility resources is given and a flexibility analysis of aggregates of thermal loads intended for domestic hot water heating, such as domestic electric water heaters or heat pumps, has been carried out during the research activity. A Monte Carlo approach is adopted for the methodology applied to the study case of Italy and Sicily. Chapter 5 describes and presents the results of the project ”Model Predictive Control for frequency regulation services provision” where the fast frequency reserve service is explored according to the related pilot project by using Model Predictive Control (MPC) based techniques applied on systems with RESs and Battery Energy Storage Systems (BESSs). Such service is meant to replace the beneficial effect of inertia from the traditional generating units which is progressively decreasing because of the implementation of RESs units in the power system. The decrease of inertia leads to more significant frequency variations after fault events that must be solved within extremely high speed actions, even faster than primary frequency regulation service. To complete the thesis, the Conclusions are presented together with some last comments. Finally, the publications produced during the Ph.D. and the projects to which contribution was given, collaborations and attended courses are listed, while references cited in this thesis end the dissertation.