## 1 Introduction  
Decarbonization of the power sector, increase of energy efficiency and energy security are the major focus of several policies to achieve ambitious climate targets in the next years [1, 2]. In the evolution of the energy systems, renewable energy sources (RES) play a major role towards the achievement of environmental sustainability [3, 4, 5]. Due to their stochastic nature, however, renewable energies are not programmable so their energy generation is usually not adjusted in order to match electricity demands [6, 7]. To guarantee the stability of the power grids, the instant balance of temporal and spatial mismatch between generation and loads can be achieved introducing flexible elements in the power networks [8, 9, 10, 11, 12, 13]. Flexibility is defined as the capability to balance rapid changes in power generation according to [PERSON] et al. [14] or variation and uncertainty in net load according to [PERSON] et al. [15]. Several definitions of flexibility can be found in the literature [15, 16, 17, 18]. Power-to-heat (PtH), based on the conversion of electricity into heat and its reverse process Heat-to-Power (HtP), are well recognized processes among the most mature demand-side management (DSM) options [19, 20, 21]. These techniques are particularly promising to provide renewable energy integration, power grid flexibility [12; 13; 22; 23] and power sector decarbonization contributing to a better utilization of existing assets supporting the RES penetration into the electricity supply mix [24; 25; 26; 27; 28; 29]. Thermal energy storage systems (TESs) can be effective in improving the mismatch between energy generation and use in terms of time, temperature, power or site leading to an increase of the overall efficiency and reliability [30; 31; 32; 33; 34]. Reduced investment and running costs, lower pollution and less greenhouse gases (GHG) emissions are some of the advantages connected to the use of these technologies [35; 36] including: sensible, latent and thermochemical storage [37; 38; 39; 40; 41]. Coupling thermal energy storage to a PtH technology to provide flexibility to the power system is a promising option of the demand-side management strategies currently investigated [42; 43]. In particular, turning surplus of variable renewable electricity (VRE) into heat to be stored as thermal energy offers a significant additional flexibility with a great potential in stabilizing the grid voltage [42; 44]. In particular, during off-peak times, heating or cooling can be generated by thermal energy and then used during peak-hours flattening the customer's load profile [45]. In this way, customers can have a more efficient system and also be cost-efficient. They can take advantage of different electricity prices during peak and off-peak hours and for utilities that can spread the demand over the whole day [46; 47]. Several studies examine the coupling of thermal storage with power-to-heat systems (PtHs) for several purposes, e.g., buffering, heating and cooling, transport of residual heat [48; 49; 50]. In general, small-scale PtH and TES applications can be applied in the residential and commercial sectors while large scale are mainly focus on industrial applications such as district heating grids [51; 52]. Storage devices have great advantages not only in terms of flexibility of the entire power system [53; 54] but also in terms of economic profitability with higher efficiency and cost effectiveness of the power grid as shown in the studies of [PERSON] et al. [55] and [PERSON] et al. [56]. In a recent study (2020) [PERSON] and [PERSON] [57] provided a detailed analysis on the potential from TESs to provide a cost-effective solution for grid level integration in the near term for renewable-based plants. Several studies show the potential of heat pumps and thermal energy storages in terms of load shifting, energy consumption and increasing self-sufficiency [58; 59; 60; 61; 62]. This work is focused on thermochemical thermal energy storage (TCTES) systems coupled with PtH technologies.