An optimized approach to design Thermal Energy Storage Tank for electricity purposes

In recent years, electricity grids have experienced rapid penetration of power generation units based on variable and unpredictable renewable energy sources such as wind and solar. These sources are crucial for the transition to a more sustainable way of generating energy and therefore in achieving both the reduction of harmful emissions and the climate targets. However, high renewable penetration leads to some negative problems associated with the intermittent and fluctuating behaviour of such sources, such as a decrease in the quality of the energy transmitted through the electrical grid and an increase in the mismatch between power production and demand. To mitigate and/or compensate for such issues, it is extremely important to identify technologies capable of both storing and delivering the surplus of renewable electricity when the production from, for example, solar and wind, is null or insufficient to cover the demand of users. In this context, over the years, numerous energy storage technologies have been studied and developed. But many of them are characterised by significant geographical and morphological constraints, such as compressed air energy storage and pumped hydro energy storage, or suffer from low energy efficiency, such as flow batteries. Among emerging energy storage technologies, Carnot batteries (CBs) offer interesting performance without stringent geographic limitations, making them an attractive solution. Among CBs, integrated thermal energy storage systems (IT-ESS) seem to be a feasible and interesting solution because of their ease of installation and compatibility with existing power plants. Despite their potential, the most important component of this technology is the sensible heat thermal energy storage unit, designed as a packed bed. However, the literature lacks precise methods for designing this storage tank, a gap that motivated the authors to develop an innovative approach to determine the optimal size of the storage device. To this end, and with the aim of properly studying a complex system with the possibility of exchanging power with both users and the electrical grid and to account for the variability of renewable sources, the sizing procedure has been investigated through an optimisation algorithm developed in the Matlab environment. At the same time, the optimal storage device volume and the proper IT-ESS management strategy have been identified. The investigation performed considers real scenarios, analysing real users and describing in an accurate way the intermittent behaviour of renewable sources.