Solar desalination systems provide a sustainable solution for freshwater production, especially in arid regions. This study evaluates the performance enhancement of a pyramid solar still (PSS) by integrating phase change material (PCM) as a thermal storage unit. An experimental investigation was conducted in the Gabe`s region, Tunisia, under real climatic conditions. Three configurations were examined a conventional passive solar still (CPSS), a PSS with 2 kg of PCM, and a PSS with 4 kg of PCM. The results demonstrate that integrating PCM significantly improves system efficiency and sustainability. The PSS with 2 kg of PCM exhibited the highest performance, achieving an energy efficiency of 32 %, an exergy efficiency of 2.023 %, a net COQ reduction of 11.11 tons, and a carbon credit gain of 161.09, with the shortest energy payback time (EPBT). In contrast, the CPSS showed the lowest efficiency 19 % energy and 1.232 % exergy, the longest EPBT, and the least environmental benefits, with a COQ reduction of only 6.65 tons. The PSS with 4 kg of PCM performed better than the CPSS but showed a slight decline in efficiency compared to the 2 kg PCM system, with an energy efficiency of 26 %, an exergy efficiency of 1.918 %, and a COQ reduction of 10.27 tons. This suggests that excessive PCM does not necessarily lead to further performance improvements. The findings confirm that integrating 2 kg of PCM provides the best balance between energy efficiency and environmental impact.