The present study investigates a passive cooling strategy for photovoltaic thermal management based on a hybrid system combining phase change material (PCM), alumina nanoparticles, and semicircular rod (SCR) fins. An experimental comparison is conducted between an uncooled reference case, a PCM-only configuration, and finned-PCM systems employing complete circular rod (CCR) and SCR fin geometries over a range of fin pitch (20% ≤ λ ≤ 33.3%) and spacing (16% ≤ δ ≤ 48%) ratios. The optimal SCR configuration is further examined with alumina nanoparticle loadings between 0.25 and 1.0 wt%. The results indicate that fin integration significantly enhances thermal regulation, with SCR fins providing greater temperature reduction than CCR designs. Under identical operating conditions, the optimal SCR configuration (λ = 20%, δ = 48%) achieves a relative temperature reduction (η) of 62.3% and limits the final surface temperature to 51.0 °C, compared to 89.0 °C for the uncooled case. Incorporating 1.0 wt% alumina nanoparticles further improve performance, yielding a maximum η of 65.9%, a minimum final temperature of 48.8 °C, and an extension of the operating period below 45 °C by 35 min. Although electrical efficiency was not directly measured, the observed reduction in operating temperature, when interpreted using established photovoltaic temperature coefficients, suggests a potential improvement in electrical performance. These findings demonstrate the effectiveness of the hybrid SCR fin and nano-PCM configuration as a fully passive approach for photovoltaic applications.