Integration of Photocatalytic Hydrogen Production with a Pem Fuel Cell-Based Off-Grid Cold Storage System: Thermodynamic, Dynamic Solar, and Environmental Performance Analysis across Three Technology Readiness Scenarios

This study presents a thermodynamic, dynamic solar, and environmental performance analysis of an integrated off-grid system combining photocatalytic hydrogen (H2) production with a proton exchange membrane (PEM) fuel cell and a vapor-compression cold storage unit (R290) for a representative Mediterranean site (Adana, Türkiye, 37.0°N). A critical methodological advance over prior simulations is the adoption of a three-scenario framework explicitly grounded in real outdoor pilot data: Scenario S1 (STH = 0.9%, TiO2-CuO/P25); Scenario S2 (STH = 2.81%, Pd/TiO2); and Scenario S3 (STH = 10%, Z-scheme heterojunction, DOE 2030 target). All three scenarios share the same 20m2 reactor aperture derived from a closed energy-balance calculation requiring the S2 system to meet the full annual cooling demand of a 400-L cabinet and identical system architecture; only the photocatalytic efficiency differs. Dynamic simulation uses 8760 hourly TMY data points from PVGIS-SARAH2. First- and second-law analyses employ the Petela solar exergy model and the Gouy - Stodola theorem. The primary objective is to determine the minimum solar-to-hydrogen (STH) efficiency at which the integrated system becomes carbon-competitive with a diesel reference, rather than to propose a deployment-ready design. A central finding is the identification of a carbon break-even STH of approximately 1.04%: below this threshold the system produces a higher lifecycle carbon footprint than the diesel reference it replaces; above it, meaningful GHG savings accumulate. S1 (STH = 0.9%), which represents the current state of practice at pilot scale, sits marginally below this threshold (system GWP = 0.356 kg CO2-eq/kWh; carbon payback 19.6 years). S2 (STH = 2.81%) crosses the threshold convincingly: system GWP = 0.184 kg CO2-eq/kWh; 42.9% GHG reduction versus diesel; carbon payback 6.3 years. S3 achieves system GWP = 0.023 kg CO2-eq/kWh and 92.9% GHG reduction. These findings provide quantitative technology targets and identify photocatalyst development as the sole rate-limiting factor for deployment.