Noninvasive photoluminescence imaging of silicon PV modules in daylight

Abstract

Outdoor photoluminescence imaging on field-deployed solar cell modules has been conducted to an increasing extent in recent years. Photoluminescence images provide more details about defects than thermal infrared images, while the imaging procedure has the potential to be faster than electroluminescence imaging because it does not require electrical connection to the modules. However, when conducted with sunlight excitation, it is based on lock-in technique, which implies switching between the modules' two operating points. This often results in the need to connect additional electrical equipment dimensioned for the task and leads to production disruption for the investigated modules. The present study demonstrates image acquisition based on the string inverter's ability to sweep the IV curve. The advantage of this approach is twofold. This is a noninvasive method, which only requires imaging apparatus and, therefore, allows for a flexible imaging procedure on the string, module, or cell level without having to take into account additional equipment. Furthermore, photoluminescence images spanning the whole IV curve can be obtained during one sweep, as opposed to obtaining images in two operating points when using lock-in technique. Such image series can be used to investigate the state of the cells and modules by looking at the photoluminescence images acquired on different current extraction levels. This has been done for a healthy string and a broken module.

Large‐Scale Daylight Photoluminescence: Automated Photovoltaic Module Operating Point Detection and Performance Loss Assessment by Quantitative Signal Analysis

“…It should be considered, that for very low irradiances around 100 W m − 2 , the influence of shunt resistance becomes dominant and DPL images look like EL images with 10% short‐circuit current injection. [ 22 ]…”

“…It should be considered, that for very low irradiances around 100 W m À2 , the influence of shunt resistance becomes dominant and DPL images look like EL images with 10% short-circuit current injection. [22] Overall, the measurements show a variation of about 6%, even after the correction of temperature and irradiance. The aim of this work was to show that the same result can be achieved between different measurements, within the uncertainties given.…”

“…A similar approach is used by Vukovic et al modulating the OP of an inverter remotely, [ 11 ] and further by exploiting the automatic IV sweep in modern inverters. [ 12 ] Images recorded during this IV sweep will include images of both OPs, which are defined and subtracted afterward.…”

“…Alternating image acquisition reduces the impact of changing irradiance during the imaging process, but it requires a very precise synchronization between the camera and the OP switching device, or a postprocessing step to separate images of different OPs, as reported by Alves dos Reis Benatto et al [ 13 ] Fast switching cannot be performed on PV modules using module‐level optimizers. [ 14 ] While most approaches described above use the alternating method, Vukovic et al [ 12 ] and Koester et al [ 9 ] used the batched method. To reduce the impact of irradiance alteration during batched imaging, Bhoopathy et al [ 14 ] introduced intensity correction by comparing an unmodulated area of the recorded images (not active PV module surface, e.g., the ground, a wall in the background, or even the cell gaps in the same PV module).…”

A review of imaging methods for detection of photoluminescence in field-installed photovoltaic modules

“…Camera detectors used for PL imaging are either silicon (Si) or indium gallium arsenide (InGaAs) detectors. For imaging outdoor, InGaAs cameras are preferred [16][17][18][19][20][21][22][23] because of their high quantum efficiency in the relevant wavelength region [8].…”