The role of sector coupling in planning the transition of a smart energy island

European Union has definitely identified the priorities towards sustainable and low-carbon energy systems recognizing a key role to islands that have been described as ideal sites to develop and test innovative strategies and solutions that will then boost the transition on the mainland. Islands energy systems are usually based on expensive and inefficient fossil fuels plants and this represents an opportunity at both environmental and economic level. Nevertheless, such transition is not a trivial task. Indeed, the integration of Variable Renewable Energy Sources (vRES) into the electricity grid is already causing technical problems to island grids thus making the grid flexibility a key topic. In the past, since power plants were completely manageable while the load was unpredictable, the grid flexibility was supplied by traditional power plants; but now, due to vRES, the variability and unpredictability has moved to the generation side and the opposite shift has happened to flexibility agents thus drawing attention to concepts such as Demand Response and Sector Coupling. In this framework of an increasingly complex energy systems, energy planning is an indispensable tool to optimally design the future energy system selecting proper renewable energy sources as well as the optimal flexibility strategies such as electric energy storage or sector coupling solutions. Energy system modelling represents one of the most used method for energy planning; indeed, energy models enable to simulate the real energy system from a technical and economic point of view. Thus, the present thesis analysed the full spectrum of energy planning in energy islands. In this context, the first step of the thesis consisted in a detailed review of the current literature, namely the following reviews were developed: • review of the existing bottom-up energy system models applied at island level highlighting the main challenges due to the insular context. Indeed, for the intrinsic characteristics of island energy systems there is the need for particular constraints and assumptions within the modelling. Maritime transport, desalination loads, congestion management (towards the mainland when connected) and security of supply are just some of the aspects that are often neglected in energy system modelling at national level and that are crucial for islands; • review of strategies and technologies that improve the ability of the grid to cope with vRES unpredictability such as energy storage technologies and all the solutions offered by sector coupling strategies. Particularly, this research focus on strategies that deal with the insular context. As regard sector coupling and Demand Side Management solutions, all the analysed solutions showed relevant results in terms of i) reduction of excess electricity production and ii) increased grid ability of hosting vRES. Then, after having identified the current gaps in the literature, specific analysis developed by the candidate on the case study of the Favignana Island are presented and discussed, namely: • application of a multi-objective optimization method for the investigation of the optimal configurations of the island energy system in 2050. In order to appropriately analyse the case study of a non-interconnected island, an additional constraint is analysed to preliminary consider the system stability. The model is used to evaluate different energy mix, based on high penetration of renewables, considering several solutions for handling the excess electricity production, namely electricity energy storage, power to heat and power to transport solutions while also improving the overall energy efficiency (i.e. solar collectors, heat pumps and electric vehicles). Results show that sector coupling solutions would lead to much greater impact in terms of carbon avoidance and economic savings managing the non-dispatchable renewable generation and maintaining the critical excess electricity production within feasible values; • a Marginal Abatement Cost (MAC) curve method is applied to optimally select the energy mix of the energy system of the island of Favignana, Italy. The considered objective function is the carbon avoidance cost so as to consider both economic and environmental aspects in a single indicator. The technologies that are considered are Photovoltaic (PV), energy storage and demand response strategies including the maritime transport and heating sectors. The decarbonisation of the maritime transport sector is of utmost importance since it contributes to almost 50% of the energy consumption and greenhouse gas emissions of the whole island and is rarely considered within an optimization. Thus, this section aims at understanding if the decarbonisation of the maritime sector should be prioritized or not; • a research investigating on the issue of water scarcity and water supply in small islands by means of a long-term energy planning model based on linear programming optimization using OSeMOSYS was developed. In this chapter, also the importance of indirect emissions of the maritime transport of goods and services (i.e. delivery of water and fossil fuels) on the whole island will be analysed in parallel with the optimization of the water supply and the optimal sizing of the RES generators (i.e. PV). Hence, the thesis proves the potential of sector coupling and DR in insular energy systems both with a literature analysis, and by demonstrating it via case study analysis by means of different models and software. It identified the current gap in literature and filled part of it with ad-hoc researches.