Selecting the glass-cover tilt angle of a single-slope solar still requires balancing optical transmission, condensate-droplet drainage, and internal air-cavity heat losses. In this study seven cover tilt angles (15°, 22°, 27°, 32°, 37°, 45°, 55°) were tested outdoors in Al Bayda, Libya (32°45′N, 21°45′E) during May–June 2024, together with internal and external planar reflector boosts. The bare-still optimum occurred at 32° — practically the local latitude — delivering 4.20 L/m²·day at 42.6% daily thermal efficiency. At shallow angles (15°, 22°), surface tension pinned droplets to the underside of the glass and over 35% of the condensate fell back into the brackish basin. At steep angles (45°, 55°), the internal air cavity expanded to ≈2.85× its 15° volume, intensifying top convective losses and dropping the yield to 3.45 and 2.85 L/m²·day. Adding polished internal wall reflectors (ρ = 0.88) at 32° raised output to 5.15 L/m²·day (+22.6%); adding a top external mirror (ρ = 0.90) pushed the peak water temperature to 84.2 °C and the daily yield to 5.85 L/m²·day (+39.3% over the 32° reference; +88.7% over the 15° still) at 54.8% thermal efficiency (defined against total intercepted radiation). Dual reflectors reduced the calculated unit water cost from $0.024/L to $0.019/L, indicating improved economic performance relative to the 32° reference configuration
Optimizing Glass Tilt Angles (15° to 55°) and Planar Reflectors in Single-Slope Solar Stills: Experimental Insights from Al Bayda, Libya
Ahmad Melad
( Department of Mechanical Power Engineering, Faculty of Engineering, University of Derna, Derna, Libya )
Majdi F. Abdulati
( Department of Mechanical Power Engineering, Faculty of Engineering, University of Derna, Derna, Libya )
Abdulqader A. A
( Department of Mechanical Power Engineering, Faculty of Engineering, University of Benghazi, Benghazi, Libya )