The Effect of Electrical Load on Photovoltaic Module Surface Temperature: An Experimental Investigation

Abstract The electrical performance and longevity of photovoltaic (PV) modules are critically affected by module temperature. The final operating temperature of a PV module under load is determined by the balance between the cooling effect of drawing electrical power and the heating effect of Joule losses in internal resistance. Simple energy balance models predict that cooling is dominant, and thus, module temperature should decrease as electrical efficiency increases. This study aims to experimentally determine the net thermal result from these opposing effects and demonstrate the role of Joule heating. Two identical PV modules were examined—one under load and another in open circuit—under clear/sunny and cloudy conditions. The findings showed that the surface temperature of the loaded module was systematically higher in both conditions. This temperature difference, averaging up to 0.9 (maximum 1.9) on a clear/sunny day and 0.5 (maximum 1.7) on a cloudy day, proves the dominance of Joule heating in internal resistance as an intrinsic heat source, rather than the cooling effect of drawing electrical power. This result reveals an inconsistency between simple energy balance models and experimental observations, emphasizing Joule heating's role in PV module thermal behavior. The findings offer important implications for improving thermal models, performance predictions, and system lifespan, especially for new high-power-density PV modules.