Daylight Electroluminescence of PV Modules in Field Installations: When Electrical Signal Modulation is Required?

With the growth of photovoltaic plant installations in quantity and size, the operations & maintenance industry calls for more efficient and accurate ways to inspect the PV modules health. To expand inspection viability, Daylight Electroluminescence (dEL) plays a big role, as EL allows accurate diagnosis of PV panels deep into the cell level. Obtaining EL images in the field during direct sunlight without covers is challenging but effective and robust using a modulated electrical signal and image processing. The thresholds required by the modulation techniques and a detailed description of how the sunlight influences the capture of the EL images are not clearly described in the research or technical literature. In this case study, our goal is to report how sun irradiance in the plane of the array influences dEL image acquisition of PV panels under direct sunlight and to better specify the irradiance limit for when modulation of the forward bias is necessary instead of constant bias. All this considering reaching the minimum acceptable EL image quality for PV diagnosis using previously available and new signal-to-noise ratio (SNR) markers.