Annual-scale experimental rear-side convective and infrared heat transfer in a tilted photovoltaic module with a phase change material

Photovoltaic (PV) modules reject absorbed solar energy through convection, long-wave radiation and transient storage. Rear-mounted phase change materials (PCMs) can reduce temperature peaks but also alter the timing and magnitude of rear-side heat rejection. Unlike previous PV-PCM studies focused mainly on temperature reduction, electrical yield or short-term and simulation-based performance, this work provides an annual-scale experimental separation of rear-side convection and infrared radiation for a tilted PV module coupled to a nominal 29 °C PCM layer (PV-PCM29) and a neighbouring reference PV. Synchronized one-minute measurements collected from 11 June 2024 to 31 May 2025 were processed using a corrected rear-surface energy balance combining selective black/gold heat-flux sensing, reconstructed rear short-wave irradiance and a differential reference-PV balance. Of 502,364 synchronized records, 125,469 paired records satisfied all comparison filters. The annual median effective convective coefficient was 5.64 W/(m2 K) for PV-PCM29 and 9.74 W/(m2 K) for the reference PV, a 42.1% assembly-level, not purely aerodynamic, reduction. Probabilistic propagation over 5000 realizations gave a 95% coverage interval of 36.5–47.1%, with the PV-PCM29 coefficient lower in every realization. In contrast, the median infrared-radiative coefficients were 5.85 and 5.88 W/(m2 K), with strongly overlapping ranges under independent emissivity perturbations. Mixed convection accounted for about 61% of paired records, while PCM-state analysis identified 433 h within the practical transition window and recurrent thermal-memory states. The results provide experimentally based, regime- and state-resolved rear-boundary data for dynamic PV-PCM modelling and show that reference-PV convective coefficients should not be transferred directly to PCM-backed configurations.