A Data-Driven Pre-Design Framework for Annual Fixed and Monthly Optimized Building-Mounted Photovoltaic Tilt Selection Using NSRDB Irradiance Data

Building-mounted photovoltaic systems are frequently constrained by roof geometry, structural capacity, mounting-system limits, shading, maintenance access, and project cost. Before these project-specific constraints are applied, designers require a transparent baseline that identifies the unconstrained irradiance-maximizing tilt and quantifies the energy value of alternative adjustment strategies. This study presents the Fixed-Tilt Photovoltaic Optimization Tool (FT-PVOT), a reproducible pre-design framework that integrates National Solar Radiation Database irradiance data with explicit solar-position and plane-of-array transposition equations. The framework evaluates candidate south-facing surface tilts from 0° to 90° at 1° increments and benchmarks annual and monthly tilt behavior against PVWatts. Using 2018–2023 data for Gainesville, FL, USA, the clear-sky annual optimum was 28–29° (mean 28.8°, standard deviation 0.41°), while the all-sky annual optimum was 29–30° (mean 29.2°, standard deviation 0.41°). Both cases closely matched the 29° PVWatts annual benchmark. Annual fixed optimization produced 3276.6 kWh/m2/year under clear-sky conditions and 2419.7 kWh/m2/year under all-sky conditions. Monthly optimization increased these values to 3394.2 and 2492.5 kWh/m2/year, respectively, corresponding to incremental gains of 117.6 kWh/m2/year (3.6%) and 72.7 kWh/m2/year (3.0%). All-sky conditions reduced annual POA irradiation by approximately 26.2% relative to clear-sky conditions but did not materially change the approximately 29° annual optimum. Monthly benchmarking against PVWatts produced mean absolute errors of 4.10° for clear-sky FT-PVOT and 4.19° for all-sky FT-PVOT, indicating that monthly prescriptions are more sensitive than annual fixed-tilt recommendations. FT-PVOT provides an auditable early-design benchmark for deciding whether more complex mounting and adjustment strategies warrant subsequent building-specific engineering evaluation.