Integrating experimental and theoretical approaches for seasonal performance analysis of an open solar photovoltaic/thermal pool system

The open solar photovoltaic/thermal pool (SSP-PV/T) system can effectively meet energy demands and extend the swimming season, yet the dynamic energy-exchange mechanism inherent to its open water surface establishes a strong seasonal dependence in system performance. To address this challenge, this study conducted grid-connected comparative experiments under summer and winter conditions to elucidate the underlying mechanisms. An inverse-problem approach was employed to compare the theoretical heat-exchange model of the swimming pool with experimental data, thereby identifying the influencing factors of various heat gain and heat loss components. The results show that the winter peak photovoltaic efficiency exceeded the summer value. During the effective operating period, the total efficiency of the hybrid photovoltaic/thermal module was 44.28% in summer and 39.70% in winter, while the total system efficiency was 37.91% and 37.17%, respectively. The average evaporative loss rate reached 1.30 MJ/h in summer and 1.22 MJ/h in winter, constituting approximately 70% of the total pool heat loss in both seasons. The convective loss rate was 0.27 MJ/h in summer compared to 0.14 MJ/h in winter. The radiative loss rate was higher in winter at 0.30 MJ/h compared to 0.27 MJ/h in summer. These findings provide a theoretical basis for the seasonal operation and regulation of the SSP-PV/T system.