Power-to-X strategies for energy system decarbonisation: a multi-scale analysis

Moving towards 100% renewable energy systems is crucial to mitigate the dramatic effects of human-induced climate change. In the next years, the large-scale RES integration is the main challenge for energy planners, because of their variability and unpredictability. Therefore system flexibility must shift from the generation phase, which has characterised fossil-based energy systems, to the conversion and storage phases and to the demand-side. In the energy planning at different scales, Power-to-X strategies and sector coupling concept emerge in literature as the key systems to integrate high RES shares and decarbonise energy sectors. The concept of Smart Energy Systems therefore has established itself as the indispensable approach for the design of future energy systems. In this framework, the aim of the thesis is to analyse technical and economic implications of sector coupling strategies to decarbonise energy systems at different scales. The main purpose is to identify criticalities and peculiarities of Power-to-X systems in the different phases of the energy transition. In detail, two scales of analysis are considered in order to assess the potential application in renewable energy communities and national energy planning studies. The analysis concerning renewable energy communities is aimed at maximising self-consumption and minimising annual costs. The strengths and weaknesses of three main strategies (Power-to-Gas, Power-to-Heat and Power-to-Vehicle) have been investigated. The role of cross-sector integration in national energy planning has been analysed from different perspectives. The Smart Energy System approach has been applied to the Italian energy system planning in order to achieve the decarbonisation targets of 2030 and 2050, by means of both static and long-term energy modelling tools. In detail, perspectives of the hydrogen role in future energy systems and the technical-economic implications of the targets set by the Italian and European hydrogen strategies have been analysed. Finally, the issue of contextualising distributed energy systems in a national energy system undergoing a radical transition towards complete decarbonisation has been analysed. In both distributed energy systems and national energy planning, electrifying thermal demand and light transport is a critical component that provides substantial flexibility to the overall energy system. This study highlights that implementing Power-to-Heat and Power-to-Vehicle strategies is more cost-effective and beneficial for enhancing energy selfconsumption than stationary electric ba􀄴eries. In the short to medium term, integrating RES generation with the heating sector and light-duty transport can help achieve the 2030 decarbonization targets. To minimise the decarbonisation costs, such strategies are also more important than the additional installation of renewable capacity. Hydrogen is expected to play a pivotal role in future energy systems; however, its use in transportation and industry is not yet cost-effective for achieving 2030 decarbonization targets. Nevertheless, it is crucial to invest in electrolyser capacities to move along the learning curve and advance the development of these cu􀄴ing-edge technologies. In decarbonised energy systems, roughly one-third of electricity generation will be allocated to hydrogen production, serving as both a flexibility system and a decarbonisation vector for hard-to-abate sectors. The analysis of these sectors is crucial for planning 100% renewable energy systems. Indeed, the strategies to decarbonise heavy-duty transport and industry heating demand affect the whole energy system configuration. Synergies between biomass and electro-fuels by means of hydrogenation processes tun out to be a promising solution in both energy and economic terms. In future decarbonized energy systems, Power-to-X technologies will be indispensable for balancing intermittent renewable energy generation, allowing for systems with a very high share of variable renewable energy sources (VRES), up to 95%. As well as energy systems are moving towards integration between sectors, energy planning cannot evaluate one sector at a time, but all strategies must be investigated by analysing synergies and impacts on the whole system. Therefore, the combined simulation of different measures is crucial for a comprehensive assessment. The combined simulation of different measures within the national energy system is crucial for the appropriate assessment of their impact, especially when the analysis includes both renewable power plant installations and sector coupling measures. The thesis proposes several methodological approaches for assessing the impact of interdependent measures and identifying the appropriate level of implementation for each strategy. An implementation matrix is suggested for the energy transition process. Furthermore, both the development of combined indicators and the application of multiobjective optimisations turn out to be viable solutions to be integrated in the energy planning process. The last issue analysed in this paper is the contextualisation of grid-connected distributed energy systems in the energy transition, suggesting a method to calculate primary energy and emission factors based on the renewable share in electricity and gas grids. Analysing the building energy performance in its current state without contextualising it and predicting the evolution of exogenous parameters, may even lead to an incorrect choice of plant configuration. Such issue should lead to modify national regulations, which, by not taking into account the energy system evolution, risk penalising heat pump systems and delaying the transition towards full electrification of building stock.