## 6 Comparing Performance of Composite Solar Walls with Sensible vs. Latent Heat Storage  
To compare the energy efficiency of the storage type of composite solar wall, numerical simulations were carried out using the material characteristics identified in a previous work published in [69]. The two materials characterized are a cement mortar (CM) and a cement mortar containing 19% by weight of micro-encapsulated PCM (M+PCM). The PCM used is Micronal(r) PCM DS 5001 X, i.e., the same as that incorporated into the experimental solar wall studied herein. Previous works highlighted that the micro-encapsulated PCM incorporated into mortar allows for 41% more energy to be stored compared to cement mortar. The thermophysical parameters of these materials are reported in Table 4 below. These same materials were introduced into the composite Trombe wall model to run the simulations. The simulations were conducted with the meteorological data presented in Section 3 and used to validate the solar wall model in the previous section. To compare the two storage types, the temperature on both sides of the storage wall and the power released by the ventilated air layer are presented in Figures 15 and 16. As regards the temperature on both sides of the storage wall (see Figure 15), no major differences exist, except before midnight when the storage wall energy released and temperature decrease. At these times, inflections in the \(\mathrm{T_{ext,m+pcm}}\) and \(\mathrm{T_{int,m+pcm}}\) curves can be detected. For the cement mortar + PCM storage wall, PCM solidifies and releases latent heat, in which case the storage wall remains warmer longer. As such, the cement mortar + PCM storage wall can release energy later, which helps avoid reverse thermocirculation (as highlighted in Figure 16 by negative powers for the cement mortar storage). In considering the energy supplied by the two solar walls, the energy balance over the study period equals 4.5 kW/m\({}^{2}\) for the solar wall equipped with cement mortar storage and 3.9 kW/m\({}^{2}\) for the solar wall equipped with mortar + PCM storage. Surprisingly, the solar wall capable of storing more energy is not the more efficient. The possible reason for this finding is either a lower transfer rate or a different energy storage than initially thought. The first reason pertains to the fact that \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Material**} & \multirow{2}{*}{**Mortar**} & \multicolumn{2}{c}{**PCM-M**} \\  & & **Solid State \(|\) Liquid State** \\ \hline Thermal Conductivity (W.m\({}^{-1}\).K\({}^{-1}\)) & 0.65 & 0.37 \\ Heat Capacity (J.kg\({}^{-1}\).K\({}^{-1}\)) & 925 & 1255; 1238 \\ Latent Heat (J.kg\({}^{-1}\)) & — & 19,520 \\ Density (kg.m\({}^{-3}\)) & 2001 & 1248 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Material properties. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Symbol** & **Explanation** & **Unit** & **Value** \\ \hline Solar energy & E\({}_{\text{sol}}\) & energy & kWh/m\({}^{2}\) & 21.4 \\ \hline Energy absorbed & E\({}_{\text{pcm,ext,cal}}\) & energy & kWh/m\({}^{2}\) & 7.8 \\  & E\({}_{\text{pcm,ext,exp}}\) & energy & kWh/m\({}^{2}\) & 7.7 \\  & - & variance & \% & 1.3 \\ \hline Solar release & E\({}_{\text{pcm,int,cal}}\) & energy & kWh/m\({}^{2}\) & 5.1 \\  & E\({}_{\text{pcm,int,exp}}\) & energy & kWh/m\({}^{2}\) & 4.7 \\  & - & variance & \% & 7.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of thermal energy results from calculation and experimental methods. thermal conductivity is almost 1.75 times lower for cement mortar with PCM. Furthermore, if the solar wall operating temperature range were to be examined, it would differ from that of the study cited [69]. In that previous study, the temperature range spanned 28 \({}^{\circ}\)C (between 11.4 \({}^{\circ}\)C and 39.4 \({}^{\circ}\)C), while the thermal capacity was 41% greater for the mortar integrating PCM.