Evaluating the performance of spherical and hemispherical solar stills with various configurations–A detailed review

• Provides a critical comparative review of spherical and hemispherical solar stills. • Quantitative synthesis identifies key performance and productivity trends. • Integration of nanomaterials, PCMs, and reflectors enhances yield by over 100%. • Evaluating the economic feasibility and environmental sustainability of each design. • Outlines research gaps and future potential including AI-driven optimization. Global water scarcity has become a critical global challenge, posing serious obstacles to sustainable development. Therefore, conducting an analytical comparison of various solar still configurations from both economic and practical perspectives is essential. Solar distillation has emerged as a promising and sustainable technology within the renewable energy sector, providing an effective solution for purifying saline and brackish water to produce potable water suitable for human consumption. Although extensive research has been conducted to enhance the performance of solar stills, identifying the most efficient and sustainable design for both industrial and domestic applications remains a major challenge. This review aims to evaluate and compare the productivity of hemispherical and spherical solar stills, focusing on the factors influencing their efficiency and examining recent experimental and analytical findings under different operational conditions. The analysis indicates that design innovations in solar distillation systems can significantly improve both efficiency and freshwater yield. For example, incorporating parabolic reflectors has been shown to enhance the productivity of spherical and hemispherical stills by 35% to 70%. Similarly, innovative design modifications — such as rotating spheres and optimized bowl geometries — have resulted in considerable efficiency improvements. Furthermore, integrating vacuum generation technology has demonstrated the potential to increase water output by 50% to 70%. The application of nanomaterials, particularly Nano-Enhanced Phase Change Materials (NPCMs), has achieved up to a 116.5% improvement in the performance of spherical stills, resulting in a daily water yield of 7.62 kg/m². Among all configurations evaluated, the NPCM-equipped spherical still exhibited the highest overall efficiency and productivity, confirming its potential as a leading sustainable desalination design.