Abstract
In past few years, the majority of the worldwide Countries realized that it was urgent to modify the current energy paradigm, mainly based on the utilization of fossil fuels. The present trend in terms of consumption of fossil fuels and emissions of greenhouse gases is posing severe issues in terms of environmental sustainability of this paradigm. Therefore, a significant effort has been performed in order to promote the transition from the present scenario to a novel one, based on the utilization of renewable energy sources. Moreover, the recent events - pandemic and Ukrainian war - are more and more pushing policymakers to promote the transition toward a fully renewable energy system. Thus, a twofold goal can be achieved. First, the continuous increase of the world average temperature can be mitigated. Then, Countries energy security and dependency can be enhanced by exploiting locally available renewable energy sources. The goal of the full decarbonization, expected in European Union by 2050, can be achieved by a double strategy: i) improving the efficiency of the existing energy networks and systems; ii) increasing the share of the energy produced by renewable energy sources. In this framework, a huge contribution is expected by the increase of the installed power capacity of wind turbines and photovoltaic collectors. Both wind and solar sources are worldwide abundantly available, and a large unexploited potential exists in several Countries. Unfortunately, these renewable energy sources are remarkably fluctuating and unpredictable. Therefore, their integration in present and future energy networks is a very challenging task, due to the significant phase shift between energy supply and demand. Suitable energy storage systems should be used to mitigate this phenomenon. Thermal storage systems are commercially mature and available. Conversely, electrical storage systems are available only for limited capacities and they are featured by high capital costs and low power densities. Simultaneously, modern and efficient energy networks are becoming more and more mature. Smart grids are nowadays used in a plurality of applications. As for the heating and cooling, the state of the art is based on the use of 4th and 5th generation district heating and cooling networks. Therefore, the integration of renewables in such modern energy networks requires the integration of novel technologies to achieve an optimal matching between energy demand and supply. In this framework the Power-to-X technology is becoming more and more attracting. According to this novel paradigm, all the excess electricity produced by renewables, which cannot be stored in the available storage systems, is converted in another energy vector or fuel (X). The most common configuration is Power-to-Heat (P2H) technology, where the excess electricity is converted into heat by using heat pumps. This heat can be stored in suitable thermal energy storage systems and used for a plurality of purposes (space heating, domestic hot water, industrial processes, etc) In the Power-to-hydrogen (P2H2) configuration, the excess renewable electricity is supplied to an electrolyzer which splits water into oxygen and hydrogen. Oxygen can be used for industrial or medical purposes, whereas hydrogen can be used for a plurality of scopes (energy conversion, transport, chemical industry, food industry, etc). It is worth noting that hydrogen use does not determine any production of greenhouse gases. In the Power-to-Power (P2P) arrangement, the produced hydrogen is first stored and subsequently supplied to a fuel cell, which can produce electricity and heat. Thus, P2P system can be used as an electrical storage system, showing attractive storage capacities and economic performance. Finally, another possibility consists in the power-to-gas (P2G) arrangement. Here, the excess electricity is used to produce hydrogen by water electrolysis. Hydrogen is stored in suitable tanks. Simultaneously, the exhaust gases of a conventional power plant fueled by fossil fuels pass trough a CO2 separation unit. Thus, the produced hydrogen can be combined with this CO2 in a methanator, for the production of methane. A plurality of technologies are available for the implementation of all the above mentioned P2X arrangements. Similarly, dozens of scientific approaches are used to design and dynamically simulate such systems. The lecture will summarize both technologies and methodologies, also analyzing the integration of P2X technology in modern energy networks. Special attention is paid to the developed control strategies and optimization techniques, implemented to improve both design and operating efficiency of the system.