Operational Assessment of a Modular Rear-Mounted Liquid-Based Photovoltaic/Thermal System under Field Conditions

Photovoltaic/thermal (PV/T) systems can simultaneously generate electricity and recover thermal energy, offering potential for improved renewable energy utilization in buildings. However, field-based evidence of the operating characteristics of liquid-based PV/T systems under actual outdoor conditions remains limited. This study evaluated the electrical and thermal performance of a modular liquid-based PV/T system using two weeks of field monitoring data collected from 15 to 28 June 2025. The system employed a rear-mounted liquid heat exchanger independently attached to a commercial photovoltaic module, enabling simultaneous electricity generation and thermal energy recovery. Electrical power output, electrical efficiency, useful thermal power, and thermal efficiency were calculated from measured irradiance, electrical, fluid-temperature, and flow-rate data. The time-of-day averaged electrical efficiency ranged from 5.18% to 5.89%, with a mean value of 5.44%. The time-of-day averaged thermal efficiency ranged from − 5.30% to 13.38%, with a mean value of 4.06%. Negative thermal efficiency occurred during several afternoon periods when the inlet fluid temperature exceeded the outlet temperature, indicating that the thermal recovery performance was affected by the thermal state of the closed-loop system as well as incident solar irradiance. These findings characterize the short-term field operating behavior of the investigated modular liquid-based PV/T system and indicate that the thermal state of the closed-loop circuit should be considered when interpreting heat-recovery performance under field conditions.