Waste heat accumulation in photovoltaic (PV) modules can adversely affect electrical performance, while a substantial fraction of absorbed solar energy remains unutilized. This study experimentally investigates the transient thermal response and waste heat recovery of a passive PV–TEG–PCM hybrid system under tropical outdoor conditions. Three configurations, namely conventional PV, PV–TEG, and PV–TEG–PCM, were simultaneously evaluated using identical 30 W monocrystalline PV modules, twenty Bi₂Te₃ thermoelectric modules in a 4S5P configuration, an aluminum heat sink, and a paraffin-based phase change material (PCM). The results show that PCM integration increased the maximum measured TEG temperature gradient from approximately 4.3 to 5.6 °C, corresponding to a 65.77% increase in peak TEG power from 2.56 to 4.24 mW. However, the absolute increase was only 1.68 mW, and the TEG contribution remained below 0.06% of the total electrical output. The Effective Temperature Gradient Duration increased from 165.68 to 174.88 min (5.56%), while the Cumulative Temperature Gradient Exposure (CTGE) increased from 1023.25 to 1049.75 °C·min (2.59%). Cumulative TEG electrical energy increased from 25.02 to 25.91 J (3.56%), consistent with the higher cumulative temperature-gradient exposure. Stage-dependent analysis showed that the average temperature gradient was 25.95% higher for PV–TEG–PCM during the initial thermal-storage regime but 34.68% lower during the later thermal-response period. These results indicate that PCM primarily modifies the transient thermal pathway by delaying the rise of the TEG cold-side temperature and sustaining favorable temperature-gradient conditions. The Effective Temperature Gradient Duration and CTGE are therefore proposed as complementary indicators for characterizing thermal-gradient persistence and cumulative exposure under the tested transient outdoor conditions. Broader applicability requires validation under multiple operating days, weather conditions, PCM properties, and system configurations