Performance Prediction Model for a Hybrid PVT System

Abstract

Photovoltaic cells convert, depending on the cell type, 6-18% of the incoming solar radiation into electricity with a higher percentage converted into heat. The heat in turn affects the cell temperature which has direct impact on its efficiency. In literature, both water and air have been used for PV cooling through a thermal unit attached to the back of the module yielding a photovoltaic-thermal (PVT) system. But the use of water requires more extensive modifications to prevent leakage and corrosion. Hence, an air channel operating on forced convection that would substantially improve the heat transfer aspects was chosen. This study investigates the performance of a low-cost heat-extraction improvement in the channel of a PVT air system that achieves higher thermal output and PV cooling while keeping the electrical efficiency at acceptable level. This study presents the use of a "helical insert" along the air channel as heat transfer augmentation that improves the PVT system's overall performance. Based on energy balance of each component of PVT system, an analytical expression for the temperature of the PV module, back wall and the outlet air has been derived. The developed model was first validated with the experimental data obtained by researchers. By confirming a good agreement with the experimental data, simulations were carried out to optimize various operating parameters, like the channel hydraulics, air mass flow rate, twist angle of helical insert and number of inserts. Then the steady-state thermal efficiency of the modified system equipped with helical insert is compared with those of typical PVT air systems. The modification results in a substantial increase m the overall thermal and electrical efficiencies to about 66.5% and 13.5%, respectively. Hence, these techniques would positively impact the applications of PV systems, more specifically Building Integrated Photovoltaics (BIPV).