Experimental Investigation and Theoretical Validation of a Thermally Enhanced Solar Still Integrating Paraffin Wax PCM and External Glass-Cover Cooling

The influence of phase change material (PCM) concentration on solar still performance has received limited attention despite its importance for optimizing thermal energy storage and freshwater production. This study experimentally and theoretically investigated a 0.25 m² conventional single-slope solar still enhanced with paraffin wax (PW) and external glass-cover cooling under the climatic conditions of Tabuk City, Saudi Arabia. Experiments were conducted at a constant basin − water depth of 0.50 cm using PW loadings of 25%, 50%, and 100 wt.% relative to the basin − water mass. Glass − cover cooling was investigated for the conventional still and in combination with 50 wt.% PW. A transient heat − and mass − transfer model was also developed to predict temperatures and hourly freshwater productivity. The results showed that 50 wt.% PW achieved the highest productivity among the PCM-only configurations (3.60 L·m⁻²·day⁻¹), whereas 100 wt.% PW reduced performance because of increased thermal inertia. Glass − cover cooling increased productivity from 2.49 to 3.41 L·m⁻²·day⁻¹ and thermal efficiency from 46.01% to 54.24%. Combining 50 wt.% PW with glass − cover cooling achieved the highest productivity of 5.10 L·m⁻²·day⁻¹, approximately 106% higher than the conventional still. Experimental repeatability, spatial glass-temperature uncertainty, and statistical model assessments were performed to evaluate measurement reliability and model performance. These analyses demonstrated good experimental consistency, while the model reasonably captured the overall temperature and productivity trends. Overall, the findings highlight the importance of optimizing PCM loading and combining PW with glass-cover cooling to enhance solar-still performance.