Conventional fixed-tilt flat-plate solar water heaters often suffer from reduced efficiency due to seasonal variations in solar radiation, leading to greater dependence on unreliable and costly grid electricity for hot water supply in Nigerian pre-primary educational institutions. This study simulated, fabricated, experimentally tested, and validated an active serpentine flat-plate solar water heater (collector area 2.04 m², storage tank capacity 65 dm3) designed to provide hot water at 50 °C for pre-primary schools in Bauchi, Nigeria. System sizing and optimal collector tilt angles (monthly, quarterly, and annual) were determined using MATLAB. Thermal performance was simulated in TRNSYS 16 with Typical Meteorological Year (TMY) data for Bauchi. The prototype was tested under monthly optimal tilt during February-April 2025, with hourly temperature measurements using calibrated thermocouples. Model accuracy was assessed via root mean square error (RMSE) and Nash-Sutcliffe efficiency (NSE). Simulation results showed that monthly optimal tilt outperformed quarterly and fixed-latitude configurations, achieving the target 50°C by 09:00 h in most months and a peak of 82°C in April. Experimental validation indicated strong agreement (highest RMSE = 2.71°C in March; NSE = 0.92 in April), with experimental peaks reaching 85°C at 15:00 h in April. Economic analysis revealed that the ₦439,616 initial investment ...
