Dottorato in ENERGIA E AMBIENTE

Titolo della tesi: 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 are one of the most vulnerable areas for the impacts of climate change. Islands have energy systems usually based on expensive fossil fuels imports and this represents a big opportunity at both environmental and economic level. Moreover, islands can be seen as frontrunners in the energy transition. Indeed, the European Union identified islands as perfect sites to implement innovative solutions to boost the energy transition towards a sustainable, independent, secure and low carbon energy system. Nevertheless, such transition is not a trivial task. Indeed, the integration of Variable Renewable Energy Sources (vRES) into the electricity grid are 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. 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 functioning as well as its operation costs. 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 carried on: • review of the existing bottom-up energy system models applied at island level highlighting the main challenges of the research field. 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 might be crucial for islands. The aim of the paper is to answer the following research questions: i) which energy system models are mostly used at island level? ii) Are national scale models also used for island applications? If yes, which type of additional constraints or adaptations are implemented? iii) A classification of these constraints will be provided in the paper. iv) Which are the main challenges of energy system models applied at insular level? • review of solutions 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 solutions that deals with such solutions in the insular contexts. Several solutions have been presented concluding that battery energy systems and pumped hydro energy storage are the most used technologies in islands. 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. Nevertheless, some of the current gaps in literature have been pinpointed and future research challenge and opportunities have been suggested. Then, after having identified the current gaps in the literature specific analysis developed by the candidate have been developed, namely: • application of the 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) and to improve the overall energy efficiency (i.e. solar collectors and heat pumps). 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. Results show that Favignana should indeed bet on photovoltaic and if vehicle-to-grid strategies are largely adopted the need for electricity storages is strongly reduced. • In this research, 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. Particularly, the EPLANoptMAC software will be used. It is based on the widely used EnergyPLAN software and the already tested EPLANopt model. Indeed, EPLANoptMAC represents an addition of EPLANopt that has been improved to produce model-based MAC curves. The objective function will be the carbon avoidance cost so as to consider both economic and environmental aspects in a single indicator. The technologies that will be taken into consideration are Photovoltaic, 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. This is considered a novelty since very few researches dealing with energy modelling and/or planning at island level optimise maritime transport while some more analyse it by means of simulation. • 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 the maritime transport sector 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).