Development of experimentally-validated models for nocturnal cooling of thermal systems with photovoltaic thermal (PVT) modules

This present work describes the development of an experimentally-validated (i) detailed mathematical model and (ii) simplified regression model, for the purpose of investigating the thermal performance of photovoltaic thermal (PVT) modules undergoing nocturnal cooling of thermal systems. The detailed mathematical model is useful for hourly, detailed simulation of thermal systems, while the simplified regression model is applicable to situations needing rapid thermal performance assessment and design of PVT systems for cooling. Such models currently do not exist, owing to the difficulty in quantifying relevant thermal radiation parameters. Thus, another outcome of this work is the foundation of a test method for quantifying cooling performance of PVT systems. In developing the detailed hourly model, the mean absolute error between the detailed model and the experiment was found to be 0.74 ± 0.91 K for predicting the fluid outlet temperature. A parametric analysis was conducted to study the effect of some physical and environmental parameters on the PVT performance, and results showed that the nocturnal cooling power increased by up to 45 W/m² under favorable radiative cooling conditions. The simplified model underpredicts the outlet fluid temperature by up to 2 °C, especially in winter, but serves as a quick, practical design tool, eliminating the necessity of complex input data and heavy computational demands. The simplified PVT performance curve has versatile applications to various thermal energy systems that benefit from integrating PVT nocturnal cooling, such as underground thermal storage reservoirs utilized with ground source heat pumps, buildings, swimming pools, and phase change material applications.