Development of an Efficient Low- and Medium-Temperature Vacuum Flat-Plate Solar Thermal Collector

Abstract

With crystalline silicon photovoltaic (PV) modules being in the market for over three decades, investigation into usual causes and extent of module degradation after prolonged exposure in field conditions is now possible. Degradation phenomena vary significantly between cells, modules and installations, giving rise to different power degradation rates reported. The main defects observed in the field-aged PV modules include EVA browning, degradation of the antireflective coating, delamination between the glass-encapsulant and the cell-encapsulant interfaces, humidity ingress, corrosion of busbars and contacts, shunt paths, cracks/micro-cracks in the cell, damage of the glass and the back sealing and bypass diode failure. This study presents severe degradation effects observed in PV modules operating outdoors for over 20 years. In many of the cases investigated, different defects were found to coexist within the same cell or module, leading to more severe effects of optical/physical, thermal and electrical degradation phenomena, significantly reducing the PV power output. Other modules that exhibited extensive optical/physical degradation showed milder degradation in performance. Detection of module degradation was carried out in this study first through visual inspection and I-V curve analysis. Further, nondestructive diagnostic techniques were used such as infrared thermography for the identification of hot spots and these were seen to be mainly linked to resistive busbars and contacts and electroluminescence imaging for the identification of shunts and other defects. The detection, diagnosis and monitoring of such defects is of great importance for a deeper understanding of the complex ageing mechanisms that take place after prolonged PV exposure in field conditions, and the identification of underlying causes, assisting the early identification of defects and the extension of the energy life of PV systems.