Evaluation of the Impact of Temperature on the Performance of Photovoltaic Solar Panels Installed on Various Roofing Sheets

Abstract

The performance and efficiency of Photovoltaic (PV) Modules are usually rated under standard test conditions (STC). However, PV modules operate over a wide range of environmental conditions at the field, which are further affected by the method of installation, especially when it comes to roof-mount systems, as different roofing materials are used for roofing houses and solar modules are mounted on them directly. In this study the effect of temperature on the output performance of photovoltaic modules mounted on four different roofing materials (stone coated, long span aluminum, corrugated zinc and short span aluminum) is investigated. Solar panels are separately installed directly on, and then elevated over, different types of roofing sheets. Results show that module installed directly on stone coated roofing material had an overall output performance of 89.52% followed by short span, long span aluminum, and corrugated zinc roofing materials with performances of 89.40%, 89.32%, and 85.54%, respectively. For the elevated set up, the same modules showed improved output performances of 96.16%, 90.30%, 89.30% and 87.84% for stone coated, long span, short span aluminum and corrugated zinc, respectively. The best output performance by the elevated stone coated roof type may be attributed to the fact that the roofing material absorbs nearly all the solar radiation thereby reflecting very little radiation back on the module. The converse is also true for the corrugated zinc material, which had the least output performance. Modules mounted directly on the roof show a strong correlation between the roof and module temperatures with the corrugated zinc roofing sheet showing the strongest correlation with a coefficient of 0.980 while for modules elevated above the rooftop the stone coated roofing sheet showed the strongest correlation with a coefficient of 0.888. For optimum performance, it is recommended that panels mounted on rooftops be elevated above the roof.