This experimental study evaluates the thermal-hydraulic performance of a pyramid solar still desalination unit (PSSDU) enhanced through geometric modification, incorporation of a floating cellulose fiber thermal layer, and controlled auxiliary heat input simulating low-grade waste heat. Experiments were conducted under typical Egyptian summer conditions in two sequential stages to isolate the influence of design and operating parameters. Initially, the effect of glass cover inclination was examined at 35° and 45°. Increasing the tilt angle to 45° enhanced vapor condensation and improved droplet drainage, raising the maximum instantaneous productivity from 370 to 410 mL/m²·h (10.8% increase), and achieving approximately 64% higher output compared with the conventional reference configuration (250 mL/m²·h ). In the second stage, a 75 mm floating cellulose fiber layer was introduced at the brine surface to enhance thermal absorption and reduce convective heat losses, while a uniform external heat flux of 600 W/m² was applied to simulate recoverable waste heat. At 100 mm water depth, the maximum instantaneous productivity reached 560 mL/m²·h . Reducing saline water depth to 25 mm intensified evaporative heat transfer, yielding a peak value of 600 mL/m²·h , corresponding to a 140% enhancement over the baseline. The maximum cumulative daily distillate production increased from 2.6 to 7.3 L/m²·day (181% improvement). Concurrently, maximum thermal efficiency increased from 26.00% to 46.00%, representing a 77% enhancement. The findings demonstrate that integrating geometric optimization, surface thermal augmentation …