Convective heat transfer coefficient for realistic turbulence parameters using LES vs. RANS turbulence models in case of free-standing photovoltaic panel

The efficiency of photovoltaic (PV) and hybrid photovoltaic-thermal (PVT) solar panels partly depends on the heat transfer to the ambient air. The exact value of the convective heat transfer coefficient (HTC) is particularly important for the development of cooling techniques. The HTC values are usually determined from experimental data available for flat plates and similar geometries. Since the HTC depends on the geometrical details of the PV panel and the environment, the HTC values are usually estimated using computational fluid dynamics (CFD) based on the Reynolds-averaged Navier-Stokes equations (RANS). In this work, a free-standing PV panel is considered, and the main objective of the work is to compare the RANS results with the large eddy simulation (LES), which is expected to provide more reliable results compared to the available experimental data. The research includes the effects of inlet velocity, turbulence intensity and turbulence length scale. It was shown that the HTC depends on both turbulence intensity and turbulence length scale. The results show that RANS models significantly overestimate the influence of inlet turbulence on the HTC, by up to 70% at high inlet turbulence intensities. Meanwhile, the LES values are within 5 % of the experimental HTC values.