## 7 Conclusions  
The primary objective of this work was to present a numerical model for simulating the thermal behavior of a composite solar wall integrating a micro-encapsulated phase change material. As a secondary objective, this model was used to compare the thermal performance of two composite solar walls, one with sensible heat storage the other relying on latent heat storage.  
The passive operations of the solar wall were first explained. This type of south-facing solar wall in the northern hemisphere is suitable for heating residential buildings during the cold weather season due to the time lag of solar gains.  
A small-scale wall was built, instrumented and exposed to real weather conditions in order to validate the numerical model developed with the Dymola software, based on the open-source Modelica modeling language. The composite solar wall entails all three modes of heat transfer. To model these transfers, the basic elements from the software's \"Building\" library were assembled. A new element was created to model heat transfers from the storage wall containing the phase change material (melting and solidification). This additional element was based on the enthalpy method developed and validated in previous studies.  
Validating the thermal behavior of the solar wall involves comparing measurements (heat flux, temperature, power released) to simulation results. This step demonstrated the model's good accuracy. The difference between experimental measurements and numerical results is less than 10% for both heat flow and energy released by the solar wall, i.e., on the order of 1 \({}^{\circ}\)C on the storage wall surfaces and less than 0.5 \({}^{\circ}\)C on the ventilated layer air temperature.  
By measuring heat flux on the storage wall over a 7-day period, it was determined that the total stored energy from the external surface corresponds to 35.8% of the incident solar energy radiating the vertical facade. 60.8% of this energy is released into the room to be heated, which is equivalent to 21.8% of the incident solar energy. A cross-correlation function calculation between the heat fluxes measured on the two storage wall surfaces (\(\phi_{\text{ext}}\) and \(\phi_{\text{int}}\)) allowed evaluating the time delay between the incident solar flux and the energy released to the room at 3 h and 4 min for a 4-cm thick storage wall including micro-encapsulated PCM.  
The study concluded with a comparison of the performance of a composite solar wall equipped with cement mortar storage (i.e., sensible heat storage) vs. the performance of the wall previously studied (latent heat storage). For purposes of this comparison, the numerical model developed and validated in the first step and the experimental meteorological data were used. It was shown that latent heat storage does not improve solar wall efficiency. The reasons cited for this finding were: a lower transfer rate due to less thermal conductivity for the latent heat storage, which stems from incorporating PCM into the cement mortar (thus lowering its density); and an operating temperature range of 45 \({}^{\circ}\)C, which is not beneficial to latent heat storage vs. sensible heat storage.  
All authors have contributed to this work. All authors have read and agreed to the published version of the manuscript.  
We would like to thank the Hauts-de-France Region and the University of Artois for the funding of LEANG's doctoral contract. Moreover, the authors are indebted to BASF for the provision of PCM.  
The authors hereby declare no conflict of interest. The funders of this work had no role whatsoever in the design of the study, or in the collection, analysis or interpretation of data, or in the writing of the manuscript, or in the decision to publish the results.