## 3 Results of Field Tests
### The Second Stage Experiments
In Figure 11e, the area over 50 \({}^{\circ}\)C is about 3.2% of the third panel, which is higher than the 1.5% threshold presumed for a normal solar module, indicating that one cell has abnormality or failure. The above description shows that 96.8% of the panel is within the normal area, as shown in Figure 11d,e. This is consistent with Figure 11a-c, showing that bright area of hot spot is clearly visible. Figure 11: Image of second stage experiment 1.3 that the solar module has cell defective. (**a**) IR origin image. (**b**) Gaussian filtered grayscale image. (**c**) Gaussian filtered color image. (**d**) Histogram of thermal temperature image. (**e**) Cumulative chart of thermal temperature image. (**f**) Cumulative chart-comparison of normal operation and abnormal conditions of solar modules. A brief conclusion can be drawn in the first case: The procedure of IR image analysis can search panels that have cells exceeding the temperature threshold effectively, as well as panels that have been confirmed to be abnormal. In the second case, the power generation efficiency is low and no obvious damage is found by visual inspection. The location of these panels is on the GPS coordinates of 24\({}^{\circ}\)05\({}^{\prime}\)45\({}^{\prime}\) N and 120\({}^{\circ}\)23\({}^{\prime}\)11\({}^{\prime}\) E with an altitude of 5 m. The nominal output of this solar farm is 40 MWp. It is the largest solar farm installed in Taiwan so far. The experiment was carried out on 7 April 7 2020, at 1 p.m. The outdoor temperature is 24 \({}^{\circ}\)C. The surface temperature of the normal operating solar module is 45-49 \({}^{\circ}\)C, and the surface temperature of the abnormal solar module is 50-55 \({}^{\circ}\)C with irradiance of 746 W/m\({}^{2}\). Only one panel was inspected with an IR image in this case. Figure 12a shows the original IR image. The image of this panel looks different because the panel is installed horizontally instead of vertically at this location. There are lots of bright areas on this panel, but the number of hot spots cannot be immediately recognized in the image. Figure 12b shows an image converted to grayscale after Gaussian filtering. Grid lines of the panel are blurred due to the filtering effect but bright areas are more visible than infrared images. Figure 12c shows a color image after Gaussian filtering to demonstrate the temperature difference on the panel that the hot area is at about 55 \({}^{\circ}\)C. Panel frames are at the temperature of 43 \({}^{\circ}\)C while the rest of the panel is at around 45-49 \({}^{\circ}\)C. Figure 12d shows a histogram of the temperature distribution. The PDF curve still looks like a beta distribution function. The mean temperature is 50 \({}^{\circ}\)C. The maximum temperature is 55 \({}^{\circ}\)C and the minimum temperature is 40 \({}^{\circ}\)C. The average temperature of this panel is relatively high and there are many defective cells causing hot spots. Figure 12e displays the cumulative temperature distribution that the percentage of hot spot area over 50 \({}^{\circ}\)C is 53.8%, indicating more than half of the cells in this panel are defective. Finally, Figures 5e and 12e are superimposed to form Figure 12f for comparing normal and abnormal conditions. Figure 12e shows that the area over 50 \({}^{\circ}\)C is about 53.8%, which is higher than the 1.5% threshold presumed for a normal solar module, indicating that 31 cells have abnormality or failure. The above description shows that only 46.2% of the panel is normal, as shown in Figure 12d,e. This is consistent with Figure 12a-c. In the third case, the power generation efficiency is normal and no obvious damage is found by visual inspection. The location of these panels is on the GPS coordinates of 24\({}^{\circ}\)03\({}^{\prime}\)59\({}^{\prime}\)N and 120\({}^{\circ}\)42\({}^{\prime}\)56\({}^{\prime}\)E with an altitude of 169 m. The nominal output of this solar farm is 6 kWp. The experiment was carried out on 20 August 2020, at 10 a.m.