Azimuth orientation effects on a fixed pentagonal-pyramid solar still in tropical conditions Nagpur, India

Solar distillation offers a sustainable solution for potable water production, yet the influence of geometric alignment on multi-face systems remains a critical but often overlooked design parameter. This work experimentally isolates the influence of azimuth orientation on the thermal and distillation performance of a fixed pentagonal pyramid solar still under the tropical summer climate of Nagpur, India. Four identical units, constructed with galvanized iron basins, internal matte black coating, thirty millimeters of polyurethane insulation, and four-millimeter-thick clear float glass, were tested simultaneously with a constant basin water depth of two centimeters. The systems were oriented toward the East (90°), West (270°), South-East (135°), and South (180°) to examine azimuth-dependent solar interception over a campaign of at least three clear sky days per configuration. The experimental results, analyzed using a validated energy balance model, determined that the south-facing orientation achieved the highest daily freshwater production of 3.6 to 3.7 L/m²·day −1 and a thermal efficiency of 38 to 40%. The South-East orientation followed with a yield of 3.3 to 3.4 L/m²·day −1 , representing a performance decrease of approximately 8 to 9% compared to the optimal south orientation. Conversely, the east-facing unit produced 2.7 to 2.9 L/m²·day −1 , while the west-facing unit yielded 2.6 to 2.7 L/m²·day −1 , both showing time-shifted productivity peaks and lower cumulative output relative to the south-aligned configuration. These findings validate azimuth alignment as a zero-cost optimization parameter, establishing south orientation as the superior strategy and South-East as a viable alternative for fixed desalination installations.