Photovoltaic thermal panels offer a practical means of generating both electricity and hot water but, at the same time, inefficiencies arise from combining these two types of collectors. This study aims to improve on convective losses in pane spacing in a covered panel by substituting the inside Air with different gases and also optimizing the distance between panes. Although a striking improvement of up to 50.4% in the convective heat loss coefficient was observed for Xenon gas with optimized spacing, the overall heat loss coefficient only improved by 8.1%, due to the significant radiative losses in comparison to convective losses in that compartment. The Xenon/Argon photovoltaic thermal panels outperform air panels in most operating conditions, up to 3.5%. However, considering economic/environmental issues, Argon appears as the most suitable filling gas. The EES code is available for future replications of the study as an 'Electronic Annex'. (c) 2015 Elsevier Ltd. All rights reserved.