Empirical investigation on the thermal behaviour of photovoltaic modules under fault conditions and localised heating

• PV module temperature increased by up to 2.8°C under open-circuit conditions. • PV faults warmed adjacent modules by + 6.8°C and near-surface air (1 m) by + 0.56°C. • Results highlight the impact of electrical faults on module and air temperatures. Undetected electrical faults in photovoltaic (PV) systems can alter module temperatures and influence rooftop thermal environments, yet empirical evidence under real operating conditions remains limited. Unlike prior studies that rely on laboratory experiments, simulations, or aggregated string-level data, this study presents a full-scale, in-situ, module-level investigation of thermal behaviour across normal (ON), open-circuit (OC), and short-circuit (SC) states, integrating surface and air temperature measurements to assess module-level and microclimatic responses. Among the tested conditions, the transition from ON to OC exhibited the most notable and statistically significant changes. Under clear-sky conditions, OC modules were +2.1°C to +2.8°C warmer than during normal operation, while the SC state produced only minor additional warming (+1.4°C) in one module type. Beyond individual surface heating, the ON → OC transition caused a measurable adjacency effect, increasing the temperature of neighbouring modules by +6.8°C, based on irradiance-normalised estimates at ∼0.95 kW/m 2 , between 14:00 h and 15:00 h. In parallel, near-surface air at 1 m warmed by +0.56°C, reinforcing the understanding that module-level heating under OC conditions can extend into the surrounding rooftop microclimate. Material characteristics further shaped these responses, with higher-efficiency, wider-bandgap modules exhibiting greater thermal stability. Collectively, the findings provide empirical evidence that PV systems function not only as renewable energy sources but also as active thermal elements influencing rooftop microclimates across operating states. These results extend PV fault research beyond purely electrical diagnostics, introducing an integrated rooftop energy-thermal perspective directly relevant to system design, performance monitoring, and urban microclimate assessment in dense tropical environments.