## 1 Introduction  
In residential buildings, the share of the final energy consumption dedicated to domestic hot water (DHW) production is estimated to be between 15% and 30% [1, 2, 3]. This share will likely rise in coming years as stricter regulations will lead, in many countries, to a reduction of space heating consumption, especially with the development of net zero energy building [3]. Thus, reducing the energy consumption of DHW production and developing technologies using renewable energies for DHW production is a major challenge for reducing the greenhouse gases emissions of the building sector. Nowadays, solar collectors are the most developed technology to produce DHW from a renewable energy source. However, the mismatch between the solar resource and the DHW demand requires the use of a thermal energy storage (TES) system. Over the past decades, hot water tanks, using only sensible heat, were the most common TES systems used to store heat production from solar collectors. However, in recent years, a growing interest in scientific research concerning latent heat thermal energy storage (LHTES) systems [4] appears as a promising alternative to conventional hot water tanks. LHTES systems use the latent heat transfers occurring during the melting and solidification processes of phase change materials (PCM) to store and release heat. The main advantage of PCM is that it is able to store a large amount of thermal energy on the phase change temperature range between solid and liquid states. Compared with conventional hot water tanks, LHTES enable a reduction in the volume of the TES system [5]. A smaller volume of DHW storage enables the reduction of thermal losses, and also creates new opportunities for the implementation of solar collectors on existing buildings. Indeed, the size of the storage is a crucial factor as the building was not initially designed to leave space for a DHW storage dedicated to solar production. In order to select the most appropriate PCM for DHW storage, it is necessary to identify the thermal properties of the PCM with a complete and accurate characterization. For example, an improvement of the accuracy on the phase change temperature from \(\pm 1\,^{\circ}\)C to \(\pm 0.25\,^{\circ}\)C leads to a reduction of 25% of the uncertainties on the heat transfers of a PCM-air unit [6]. An inaccurate characterization of thermal properties might lead to a wrong sizing of the system and to lower performances than expected. Currently, the most widespread method is to characterize PCM by direct scanning calorimeter (DSC). This method enables the identification of the enthalpy curve of the PCM with fast experiments on a small sample of a few milligrams of PCM. However, most PCM have a low thermal conductivity and there is a thermal gradient between the heat source and the internal temperature of the PCM. As the enthalpy curve of DSC experiments is computed with the heat source temperature, the thermal response of the PCM sample is influenced by the heating/cooling rate [7,8]. Moreover, for PCM experiencing supercooling, the recalescence process, defined by a short reheating of the PCM when the metastable state is broken, cannot be observed with DSC experiments, and this is for two reasons. First, as mentioned earlier, only the heat source temperature is monitored and a short increase in the PCM temperature might remain unseen by the sensor. Secondly, the sample is very small and the cooling rate of the experiments is usually too fast to enable a reheating of the PCM. In these conditions, the latent heat release during the recalescence is evacuated directly to the surroundings and is materialized by a heat flux peak. For PCM characterization with a calorimeter, the step scanning (STEP) method overcomes the dependency of the results with the heating/cooling rate [9,10]. Compared with the DSC method, where a heating/cooling rate is applied to the sample, the STEP method consists of applying temperature steps to the sample.