¹ Applied Mechanics and Energy Systems Laboratoty (LMASE), Faculty of Applied Science, University of Ouargla, Ouargla 30000, Algeria;

² Institute of Technology, University of Ouargla, Ouargla 30000, Algeria;

³ Laboratory of Promotion and Valorization of Saharan Resources (VPRS), University of Ouargla, Ouargla 30000, Algeria

* Correspondence: kemerchou.imad@univ-ouargla.dz

This study experimentally investigates the integration of paraffin-based Phase Change Material (PCM) into a solar water heating system to improve post-sunset thermal retention under Saharan climatic conditions (Ouargla, Algeria). Two PCM masses (0.5 kg and 1 kg) were tested and compared with a conventional storage tank. Results show that, while the conventional system reached a peak water temperature of 65 °C, the PCM-assisted system stabilised around 60 °C and maintained temperatures above 52 °C for nearly four additional hours after sunset due to the phase change plateau. Increasing the paraffin mass from 0.5 kg to 1 kg extended the phase change duration by approximately one hour, significantly enhancing heat retention. The analysis demonstrates that PCM integration effectively reduces thermal losses, stabilises water temperature, and improves the overall thermal performance of the solar water heater using a simple and low-cost configuration suitable for arid regions.