Deliverable D4.1 provides information and specifications for the TCM reactive material to be implemented in the Ministor thermochemical (TCM) reactor and the design of the thermochemical reactor that must be integrated in the TCM storage unit exploiting the low temperature thermal energy delivered by PVTs or FPCs collectors. The whole TCM storage process must ensure the dual function of storing the thermal energy from the solar collectors and its restitution in the form of cold during the summer or heat during winter. The first step in the development of such a system is the choice of the reactive salt capable of reacting with ammonia, the refrigerant, to meet the operating conditions of the Ministor system during the heating mode in winter and the cooling mode in summer. Ammonia (NH3) was chosen as the refrigerant fluid since it has an interesting energy density while being stable over the temperature range considered for the Ministor application. Furthermore, it meets the requirements for the development of an environmental friendly system. Calcium chloride (CaCl2) was selected over barium chloride (BaCl2) as the reactive salt using thermodynamic calculations which allow to determine the equilibrium temperatures and pressures of the reaction with ammonia. Its implementation allows suitable heat and mass transfer properties, which are strongly correlated to the thermal power and energy density of the system. Enhancements to the salt are also considered such as addition of graphite. A simplified steady-state model describing a compressor-assisted transformation of the TCM reactor during the charging phase has been developed in order to carry out the design of a TCM unit according to : the targeted energy storage of the reactive medium (TCM energy density of 200 kWh/m3 fixed in the proposal), the required storage capacity and thermal powers in accordance with thermal needs or solar energy resources, the operating conditions such as solar resource available (power, temperature, duration) and the characteristics of the selected ammonia compressor.