Thermal management of hybrid CPV, CPV-STEG, and CPV-TEG systems using flat plate heat pipes: energy, exergy, and environmental analysis

The combination of concentrated photovoltaic (CPV) with thermoelectric generator (TEG) and solar TEG (STEG) enabled an effective strategy for maximizing solar energy utilization. However, since these hybrid designs reached extremely high cell temperatures, mitigating losses became critically important. To prevent this situation and ensure thermal management, flat plate heat pipe (FPHP) emerged as a viable alternative. This study examined the influences of working fluid (water, ethanol, acetone, and R141b), wick porosity (0.3 to 0.7), and solar concentration ratio (C = 5 to 10) on six different system configurations encompassing CPV/FPHP with a channel (M1) or heat sink (M2), CPV-STEG/FPHP with a channel (M3) or heat sink (M4), and CPV-TEG/FPHP with a channel (M5) or heat sink (M6). The results revealed that M1 consistently achieved the lowest PV cell temperature on all parameters, with a maximum PV efficiency of 16.48% (C = 5, water and porosity of 0.3). Among the investigated working fluids, water demonstrated the highest thermal performance. This was followed by ethanol, acetone, and R141b, respectively. Specifically, replacing R141b with water enhanced the total output power of all configurations, providing a maximum increase of 4.90% for M3. When comparing the configurations among themselves, the channel-based models provided superior total output power than the heat sink models, where the values for M1, M3, and M5 were 2.51%, 3.31%, and 2.71% higher compared to M2, M4, and M6, respectively (water, C = 5, porosity of 0.5). Wick porosity did not cause a significant difference in the outputs of the configurations. Higher solar concentration ratios significantly enhanced TEG performance and environmental parameter values. Under C = 10 and 0.5 porosity with water, M3 outperformed other configurations by achieving the highest TEG efficiency (4.75%), exergy efficiency (29.67%), and sustainability index (SI) value (1.422). Furthermore, M3 provided the highest environmental impact, recording a lifespan C O 2 emission reduction of 58.3 kg and the highest environmental cost savings of $0.845 at C = 10. Non-TEG configurations (M1 and M2) reached highest exergy efficiencies at C = 5, which was 13.21%.