## 5 Conclusions  
In this work, to provide a comprehensive review on the state of art of thermochemical storage systems and their applications in power-to-heat technologies, theoretical, experimental and numerical studies and their recent advancements and potential perspectives were discussed. This paper reviews the current literature that refers to the development and exploitation of thermochemical storage systems connected to power-to-heat technologies to power grid support. The operation principles both of thermochemical and of power-to-heat are presented, thermochemical materials and processes are compared. Power-to-heat conversion is likely the most mature and favorable technology enabling power flexibility. It is particularly suitable in energy systems with high shares of renewable generation. In order to increase the flexibility of the energy system, power-to-heat technologies coupled to thermal storage devices are among the most promising alternatives. Thermal storage is able to provide several benefits such as load management, power quality and continuous power supply. When there is an excess of generation, electricity is converted into heat and stored for subsequent use on demand. In this way, additional power in the situations of increased load is provided, thus contributing to peak shaving, load shifting and energy conservation. The conversion of power into heat is generally performed by electrical resistances or via heat pumps. Despite converting electric power into heat is not convenient from a thermodynamic perspective, power-to-heat applications are gaining an increasing attention due to the low prices of renewable electricity and the increasing surplus of produced electricity that cannot be used. Several advantages, e.g., high efficiency for balancing excess renewable generation and high potential on reduction of CO\({}_{2}\) emissions and fossil fuels, could be the key elements for a larger development in the future trends of these technologies. There are several examples of sensible and latent thermal storage in power-to-heat applications, while only a limited number of applications of thermochemical storage in the power-to-heat field are available. High energy storage density, no heat loss during the storage, no self-discharge and long charge/discharge, broad availability and suitable temperature ranges are some important advantages of thermochemical storage systems. However, the high complexity and costs of these technologies limit the real applications, while only few prototype-scale systems have been studied. To improve their implementation, comprehensive analyses and investigations are further required. In contrast, thermochemical storage is widely used into heat-to-power sector. Heat-to-power and power-to-heat sectors are among the most relevant options available to balance fluctuating renewable energy sources and hence power grid. This particular interaction between electricity and heat sectors will play an important role towards the cost effective transition to a low carbon energy system with a high penetration of renewable generation. **Author Contributions:** All authors conceived the research idea and the framework of this review. All authors have read and approved the final manuscript. **Funding:** This research received no external funding. **Conflicts of Interest:** All authors declare no conflicts of interest.