Effect of a back surface roughness on annual performance of an air-cooled PV module

In this paper, a study of increasing a photovoltaic (PV) module efficiency via natural/forced cooling of the PV cell is presented. The PV module is cooled by the air flowing in a duct placed under a back surface of the PV panel. The cooling air is moved either by fan or naturally by the temperature difference generated from the heat transfer with a panel. The system could be applied on the roof of industrial facilities, with electrical and thermal energy needs. The presented 1-D model examines an already published thermal and electrical PV/T approach supplemented with a radiative heat transfer in the panel duct. In addition, an effect of the roughness of the panel back surface is also added to the model. The model coded in an Engineering Equation Software (EES) is capable of evaluating the PV module efficiency and other thermal parameters as the outlet air temperature and back surface temperature. As a result, the performance of the system in a typical winter and summer day is discussed. Furthermore, an annual simulation of the system is also analysed coupling the EES® model with the Trnsys software. The results of the annual simulation show that the raise of the relative roughness of the panel back surface from 0 to 0,05 leads to an increase of 0.25% of the average efficiency of the PV module in case of air moved by a fan. In terms of overall efficiency, this result means a relative improvement of 1.73%. Annual average thermal efficiency of the PV/T system of 28.6% is achieved for relative roughness of the panel back surface set to 0.05.