Maximizing Desalination Yield in a Tubular Solar Still: Experimental Study and Multivariate Analysis of Critical Parameters

Solar stills provide a simple, sustainable method for producing freshwater in arid, coastal, and remote regions where conventional desalination is often impractical. This study experimentally evaluated a tubular solar still fabricated from locally available materials under controlled indoor conditions. The thermal performance and freshwater productivity were analyzed with respect to ambient air temperature (Ta), humid air temperature (Tha), cover temperature (Tc), trough temperature (Tt), water temperature (Tw), relative humidity, artificial solar radiation intensity (Sr), and associated temperature differentials. Pearson correlation, linear regression, and principal component analysis (PCA) were employed to investigate the relationships among the measured variables. Water and trough temperatures increased rapidly and reached steady-state values of approximately 46 °C after 2 h, whereas the maximum freshwater yield reached 14.3 g/h. Freshwater yield exhibited strong positive linear relationships with the principal thermal driving forces, including Tw − Ta (R2 = 0.996), Tw − Tc (R2 = 0.989), Tha − Ta (R2 = 0.980), and Tha − Tc (R2 = 0.940), while showing a strong inverse relationship with the relative humidity difference (RHha − RHa; R2 = 0.964). The high thermal efficiency (about 75% prior to accounting for salinity effects) achieved under steady-state conditions proves that precise irradiance control minimizes heat loss. Pearson correlation analysis confirmed significant positive correlations between freshwater yield and the thermal variables (r = 0.957–0.998, p < 0.01) and significant negative correlations with the relative humidity parameters (r = −0.761 to −0.951, p < 0.01). PCA showed that the first principal component explained 83.55% of the total variance, representing the dominant thermal behavior of the system, while the first four principal components together accounted for 98.47% of the dataset variability. These findings demonstrate that freshwater productivity is primarily governed by internal thermal gradients rather than radiation intensity alone and highlight the importance of optimizing heat and mass transfer processes to improve the performance of low-cost tubular solar stills for sustainable desalination applications. These findings provide useful insight for the optimization and scale-up of tubular solar still systems for sustainable desalination applications in water-scarce regions, providing a sustainable framework to produce low-cost potable water from seawater via renewable solar energy.