## 2 Comparison of Experimental Devices
### HSLU
LTTT  
The thermal cycling device \"LTTT\" is comprised of a thermostatic bath (water or thermal oil) with a 4-channel PT100 data logger (expandable). Pictures of the device are shown in Figure 8:2  
As temperature profile, one temperature level above and one the below phase-change temperature with a rapid change between the temperature levels or with defined heating/cooling rates are applied. Up to 16 samples can be cycled simultaneously in test tubes (made of glass, metal, or plastic), which are sealed with a rubber plug and immersed in the thermostatic bath. During the experiments, temperature-time curves of the samples are measured. After a certain number of cycles, DSC measurements are performed, and the temperature curves of the samples are analyzed. Figure 8:3 Ramps of temperature and heat fluxes measurements during thermal cycling of sodium acetate trihydrate (SAT). Figure 8:4 Fluxmetric bench “LGCgE” (**a**), parallelepipedal poly (methyl methacrylate) (PMMA) sample containing PCM with the lateral heat fluxmeters before installation in the insulation (**b**). UDL-GREiA I (This Equipment Is Shared with the University of Barcelona, DIOPMA Research Group)  
The GeneQ BIOER TC-18/H(b) thermal cycler allows performing thermal cycles from room temperature up to 100 \({}^{\circ}\)C to investigate the stability of PCM samples over time. Typically, 50 K\(\cdot\)min\({}^{-1}\) is applied as the heating and cooling rate. Up to 100 thermal cycles per day are carried out. The thermal cycler allows placing 18 samples at the same time in 0.5 mL Eppendorf tubes. The Eppendorf tube must not be filled completely, as only the lower part will be subjected to heating and cooling cycles. It is recommended to fill 2/3 of the Eppendorf tube. Depending on the aim of the study, different temperature profiles can be applied. A picture of the stability testing device \"GREiA I\" is shown in Figure 8:5  
Figure 8:6 Picture of stability testing device \"UDL-GREiA I\". Figure 8:7 View of the stability testing device “LTTT” (**a**) and detailed view of the arrangement of the sample holders (**b**). UDL-GREiA II  
The pilot plant at the University of Lleida was built to accurately test different thermal energy storage (TES) systems working with latent or sensible heat storage materials. This facility is composed of a 24 kW\({}_{\text{e}}\) electrical boiler to heat up the heat transfer fluid (HTF) (acting as energy source during the charging process), different storage tanks containing PCM, and a 20 kW\({}_{\text{e}}\) air heat exchanger to cool down the HTF (acting as energy consumption). Typically, one thermal cycle per day is carried out. A picture and schematic of the pilot plant test facility are shown in Figure 8:8  
A data acquisition system consisting of temperature, pressure, and flow rate sensors as well as different data loggers and a personal computer were integrated in the facility to measure the HTF flows, HTF pressures, and HTF and PCM temperatures in the boiler and storage tank, respectively. Depending on the aim of the study, different temperature profiles are applied. In this regard, during experimental tests that are carried out to assess the performance of components such as PCM tanks under different charging and discharging conditions, thermal cycling testing of the PCM can also be realized as far as the required number of thermal cycles and the temperature profile are known. Then, the degradation of PCM after different cycles can be evaluated at a pilot-plant scale, or small samples of the PCM can be extracted and analyzed in the lab using established techniques, such as DSC, FT-IR spectroscopy, or thermogravimetric analysis (TGA).