# Low-Cost Three-Quadrant Single Solar Cell _I-V_ Tracer
## 4 Discussion  
We demonstrated that the construction of a prototype based on our theoretical strategy is practically achievable and leads to a successful \(I\)-\(V\) curve tracing of a single cell as well as a small number of cells. We solved the technical challenges encountered for the correct measurements of the voltage and current of the cell and designed all the electronics  
Figure 23: Voltage sweep in the first quadrant (voltage vs. time). AU: arbitrary units. Figure 24: Voltage sweep in the second quadrant (voltage vs. time). AU: arbitrary units. needed to ensure it. The OA level adaptor ranges were adjusted and measured against an oscilloscope for a proper conversion from the ADC values to the actual voltage values. All the sign/scale conversions that were needed to correctly interpret the raw sampled data were conducted via software on a computer program. The data were downloaded from the device; the files were saved and plotted. We have not introduced this program, written by us in Python, because it could be conducted in many ways and is now very simple (without an interface, just in the command line mode). The device was used to measure curves in more than 20 different single cells by the time (plus two mini-PV modules). These cells were of the same manufacturer and type as described in Table 1. The purpose of these measurements, in addition to demonstrating the validity of the apparatus, was to train an artificial intelligence (AI) algorithm along with its corresponding EL images, to classify cells into some groups according to their output power. These kinds of data are very difficult to obtain for the same cell, so a device such as this enables anyone to do it at a very low cost. _I-V_ tracers capable of taking good measurements at the cell level are in the price range of one thousand dollars (USD 1000) or higher. Some laboratories make them manually with two good multimeters and a programmable electronic load or via the one-capacitor charging method. One of these bank multimeters is in the range of one thousand dollars or higher, so the full equipment for an _I-V_ curve could cost around USD 3000 or higher. The components used in our device cost around fifty dollars (USD 50). Obviously, we did not charge the costs for the design, make, mounting, programming, calibrating, testing, etc. The LED illumination board components cost less than one hundred dollars (USD 100) and the 3D-printed platform cost is derisory (USD 10 in filament or less, plus the electricity consumption). The noise environment in our laboratory is quite severe, and it is expected to be more or less the same in the usual spaces where the device is intended to be used, so electromagnetic-superimposed noise was observed over the signal in the current measurements, but it did not seriously affect the shapes of the curves and could easily be eliminated by post-processing filtering. We obtained a very promising result but, as in all processes (from theory to reality), some problems arose. The first was expected and related to the illumination. It is not exactly the same to illuminate a cell with the Sun spectrum as with a single wavelength. The biggest problem with the LED board is that we needed to place it relatively close to the cell (about 10 to 15 cm) to obtain an adequate signal. At this distance, it is difficult to obtain a homogeneous irradiance at the full cell area. Each LED is a big spot with a spatial irradiation cone. To minimise this problem, a diffuser was placed below the LEDs. Even so, as can be seen in Table 3, the \(I_{\mathrm{SC}}\) obtained by us at a (supposed) irradiance of 1000 W/m\({}^{2}\) was 8.35 A, while it should ideally be 8.99 A (from the manufacturer datasheet). This is just 7% less, but it evidences that the illumination in the cell plane is not homogeneous enough, which is also obvious from the maximum power point obtained, 3.63 W experimentally versus the theoretical 4.65 W (a 22% less).