# Progress in Improving Photovoltaics Longevity
## 4 Results
### PV Operation Monitoring
#### 4.3.1 Field Monitoring Methods  
Field monitoring methods [43; 44], which are commonly applied for monitoring PV operations, are described in Table 5. The most common field monitoring method is visual inspection, which is a very popular, easy, and straightforward way to detect defects in a PV module, as it allows data collection and visual observations in a wide range. Although its detectability imposes restrictions due to the fact that several complications occurring in a material go unnoticed by the naked eye, this technique is effective, rapid, and does not require specialized equipment. \begin{table}
\begin{tabular}{c c c c} \hline
**Module** & **Degradation Modes** & **Failure Modes** & **Impact/Effects** \\
**Component** & & & \\ \hline Backsheets & Hydrolysis, photo-oxidation & Discoloration, chalking, cracking, delamination & Reduced power output, corrosion \\ \hline By-pass diodes & Overheating & Arcing, thermal leakage, electrostatic discharge & Safety risks, performance losses \\ \hline Encapsulant & Photo-oxidation, corrosion & Discoloration, delamination, material interactions & Demeaned current \\ \hline Frame & Corrosion & Loosening, deformation & Increased hazard of cell/module damage \\ \hline Frontsheets & Photo-oxidation, hydrolysis & Discoloration, cracking, delamination & Reduced power output, corrosion, optical losses \\ \hline Glass & Glass corrosion & Breakage, coating erosion & Cell or circuit damage, hot-spots emergence, moisture ingress \\ \hline Internal circuitry & Corrosion of metallization & Cracking, fatigue, contact failure & Degraded current, cell isolation, hot-spots generation \\ \hline Junction box & Corrosion, detachment & Insufficient sealing, arcs, delamination & Increased power losses, safety issues, high current \\ \hline Solar cells &
\begin{tabular}{c} LID, PID, Light- and elevated \\ temperature-induced degradation \\ (LETID) \\ \end{tabular} & Cracking & Hot-spots creation, reduced power \\ \hline \end{tabular}
\end{table} 
Table 4: Degradation and failure modes of PV module performance and their impact on the performance characteristics of the PV system [40]. Another valuable test tool for ensuring the proper operation of PV modules is the I-V curve. This method is applied to monitor and evaluate the electrical output of the module under different operating circumstances, such as levels of irradiance and variations in temperature. The parameters of the I-V curves are strongly connected to the electrical profile of the module. Discoloration, delamination, and glass corrosion can cause a drop in short-circuit current, while losses in open circuit voltage are often the result of PID, temperature-induced degradation (TID), LID, or a breakage in the cell interconnections. The slopes in each case denote an increase in shunt and series resistance, respectively. The I-V curves can be used to evaluate both the annual rate and the percentage of the degradation of the PV module. The ultraviolet fluorescence (UVF) technique is widely used to measure degradation in c-Si-based solar cells. The application of the technique requires a spectrometer and a UV irradiation source, which can be used to detect cell cracks, hot spots, and EVA degradation. The method is mainly used for an in-depth examination of the encapsulation material of a PV module [112], which is typically EVA, along with various additives, such as oxidation stabilizers and UV absorbers, and acts as an accumulation region for fluorophores. X-ray scanning is a non-destructive method applied to detect delamination and incoherence among the elements of a PV module in two-dimensional (2-D) images. Similar to the X-ray scanning method, ultrasonic inspection is based on scanning the PV module with the assistance of a moving ultrasonic transducer with an integrated X-Y indicator. Thermal or infrared imaging (IR-T) is one of the most well-known testing techniques for the detection of potential thermal abnormalities and electrical failures in a PV module.