# Evaluation of Artificial Intelligence-Based Models for Classifying Defective Photovoltaic Cells
## 2 Materials and Methods
### Materials  
A 60-cells polycrystalline module composed of cells with and without defects was used. The front and back views of the module are presented in Figure 1a,b respectively. The module was ad-hoc manufactured with all cells accessible from the backside of the module. Regarding the cell labeling, numbers from 0 to 59 have been used to identify the cell, as detailed in Figure 2. Additionally, the four corner cells have been labeled both in Figure 1a,b to facilitate understanding. Figure 1: (**a**) Front view of the module. (**b**) Back view of the module. The first string (first and second columns in the back view) contains manufacturing defects, the central string (third and fourth columns) contains soldering faults, while the third string (fifth and sixth columns in the back view) contains breaking deficiencies. The low-efficiency defects (cells 1 and 4) and medium efficiency cells (cells 14 and 17) were due to manufacturing problems, with an efficiency of 9% and 16.4% approximately, but they did correspond with breaking or short-circuited cells. Short-circuit cell (cell 6) has been generated by extending the cell connection tabs beyond the ordinary placement, short-circuiting the cell. In order to simulate the bad soldering defects, buses from the back of some cells were left without soldering, either one bus (cell 22) or two buses (cell 34). Three buses have not been left without soldering in any case as it would have meant that this cell would not be series connected as the rest. In cell 38, all tabs were lose (without soldering), although they made contact allowing module production. The cell with only 1 cm welded (cell 27) was used to simulate bad soldering, in which only 1 cm of the bus was welded instead of the typical 15 cm being welded. The third-string contains some cracked cells without cell area decrease (cell 50 and 51), with cell area decrease (cell 41, 42, 55, and 57) or a combination of both in the same cell (cell 45). When a piece of broken cell was placed on top of another cell (cells 49, 58, and 59), it generates partial shading, simulating the important aspect of permanent bird droppings. These types of defects were analyzed as they ordinarily appear in commercial modules in operation, either during manufacturing, transport, or operation. However, commercial modules are not accessible at the cell level. That is why an ad hoc module was manufactured for defect characterization. The nominal characteristics of a standard module of this type are: nominal power (P) 250 W, efficiency 15.35%, maximum power point current (Impp) 8.45 A, maximum power point voltage (Vmpp) 29.53 V, short circuit current (Isc) 8.91 A and open-circuit voltage (Voc) 37.6 V. Having 60 cells in series, the nominal values of a healthy cell were considered: nominal power 4.17 W, Impp 8.45 A, Vmpp 0.49 V, Isc 8.91 A, and Voc 0.63 V.  
I-V curve measurement (at the cell level) and EL images were carried out at the CIEMAT's facilities (Madrid, Spain). In summary, the facilities used were the following:  
* The indoor measurements have been performed in the commercial system Pasan SunSim 3 CM, which consisted of a light pulse solar simulator class AAA according to IEC 60904-9 standard, which can perform I-V curve measurements at Standard Test conditions;  
Figure 2: EL image and cell numbering for model training. * The \(EL\) and indoor \(IRT\) tests were simultaneously performed with the \(EL\) in this chamber. The module was fed with a Delta power supply SM 70-22. A Fluke 189 multimeter connected to module terminals allowing it to register the exact module voltage. \(EL\) and \(IR\) images were captured with a PCO 1300 and a FLIR SC 640 camera, respectively. In this way, the information of the \(EL\) image and I-V curve of each \(PV\) solar cell was obtained. In the following Figure 2, an \(EL\) image of the measurement module and the numbering of the cells is shown. This information could serve to validate the different models.