## 4 Discussion and Conclusions  
Performing EL measurements in PV power plants under high irradiance conditions can be challenging, as the EL signal must be modulated for background removal. Nevertheless, EL imaging remains a powerful tool for fault detection and optimizing PV plant operation. Therefore, developing new approaches that enable EL image acquisition during normal PV plant operation is highly desirable. This article has demonstrated that it is possible to modulate an arbitrary current injection in a single solar module using an electronic device that relies on the string current for self-powered modulation. The ability to modulate current using other PV modules as an energy source enables EL signal modulation without the need for an external power supply. This approach is more practical for PV power plant inspections, as it eliminates the need for disconnection, enhancing EL measurements during normal operation. Although current and string voltage variations are observed during modulation, the PV inverter continues operating. In this scenario, the analyzed case represents the worst  
Figure 9: Detailed images of damaged solar cells using the self-powered approach. Exposure time of 2 ms, 53 fps and 1000 images per sequence. case condition, as a single inverter tracks the MPP of only 10 modules. Using a larger inverter could help reduce voltage and current fluctuations. Since the injected current is directly proportional to the EL signal intensity, one might assume that the self-powered approach only works under high irradiance conditions. However, the background signal also varies linearly with irradiance, resulting in similar signal-to-background ratios across different irradiance levels. This allows the self-powered approach to be used in a wide range of scenarios. Note that wind can also significantly affect image processing, as it may cause vibrations in grass and surrounding vegetation (visible in the raw images), leading to signal variations close to the modulation frequency. Therefore, it is crucial to crop the images to analyze only the area corresponding to the solar module. The main limitation of the proposed approach is that it requires integrating a small electronic device into each PV module. Although this could have a significant cost impact, the proposed topology has strong potential for integration into module-level solar optimizers or micro-inverters, which are becoming increasingly popular. In this context, since a single electronic device would be required for each module, incorporating the proposed solution could have a minimal impact on the overall cost of the system. The total cost of the board hardware is approximately $16; however, it can be reduced to less than $10 if the design is optimized for cost (e.g., selecting alternative MOSFETs, increasing the PWM frequency to reduce the size of the LC filter, etc.). Furthermore, integration into other module-level electronics, such as microinverters or solar optimizers, allows for the omission of certain components such as the microcontroller, communication module, or power supply module, which could reduce the cost to less than $8 per board. Comparing the proposed approach with conventional measurements using a programmable power supply to modulate the EL signal, similar results can be expected from both methods. In qualitative analysis, both approaches produce comparable images, effectively revealing failures within solar cells. To quantitatively assess potential differences, the SNR was calculated across several scenarios. In this regard, both methods also yield similar results. It is important to note that the quantitative analysis of EL images is inherently complex and may not always be fully representative. However, it can serve as an indicator of measurement quality. The use of FFT has proven to be effective in successfully removing the background signal using different waveforms, including square wave, full sine wave and half sine wave.