Experimental investigation and performance optimization of a double slope solar still integrated with nanoparticles in phase change materials

• Five modified double-slope solar stills with fins, PCM, and nanoparticles. • Single/multi-objective optimization applied to all modified solar still systems. • Energy, exergy, exergo-economic, environmental impact, and sustainability assessments. • Average output of 2.28 L/day—a 270.97 % increase over conventional stills. • High-accuracy RSM model validated via ANOVA, reliable vs. experimental results. By utilizing solar energy for desalination, solar stills offer a sustainable and cost-effective means of providing fresh drinking water in remote and arid regions. Existing studies have primarily focused on improving freshwater productivity while considering economic and environmental feasibility. The present work offers an in-depth assessment of solar still (SS) systems by analyzing energy and exergy performance, exergoeconomic factors (energy-economic factor, exergoeconomic factor, and cost of water), environmental impacts (CO 2 emissions, exergo-environmental factor, and carbon credit gained), and sustainability indicators (energy payback time and sustainability index). Five different cases were examined: (I) a conventional solar still (CSS), (II) CSS with fins, (III) CSS with fins and PCM, (IV) CSS with fins, PCM, and 1 % CuO nanoparticles, and (V) CSS with fins, PCM, and 1 % Al 2 O 3 nanoparticles. Response Surface Methodology (RSM) was employed to establish a mathematical model that describes the relationship between operating factors (daytime and solar intensity) and response factors (energy efficiency, exergy efficiency, and accumulated distilled water), thereby optimizing system performance. Case IV achieved the maximum freshwater production of 3.38 L/day, representing a 270.97 % increase over the conventional CSS, along with a maximum energy efficiency increase of 76.89 % compared to Case I. The ANOVA test confirmed the accuracy of the model, as evidenced by minimal residuals and strong agreement between the predicted and experimental results. The present study contributes key insights into optimizing SS configurations for enhanced performance, sustainability, and cost-effectiveness.