Aerial Photoluminescence Imaging of Photovoltaic Modules

Abstract

On‐site imaging of modules in photovoltaic (PV) systems requires contact‐free techniques with high throughput and low cost for commercial relevance. Photoluminescence imaging satisfies these requirements, but it has so far not been used for aerial imaging. Such a system faces unique engineering and operating challenges, including the need to mount a light source on the drone and identifying module defects from images taken under low‐ and nonuniform irradiance. Herein, in‐house developed photoluminescence aerial imaging (PLAI) setup is presented and it is demonstrated that it can be used to identify defects even with a difference of excitation intensity of up to 50%. The setup consists of a hexacopter aerial drone equipped with an illumination unit and a near‐infrared camera. The unit is capable of partially illuminating full‐sized modules at night and capturing the photoluminescence response. In the maiden flight, a throughput of 13.6 PV modules per minute is achieved, and a throughput of 300 PV modules per minute is feasible. It is shown that the setup can be used to detect and identify cracks and potential induced degradation with high levels of confidence. These findings are verified by cross correlation and comparing captured photoluminescence images to electroluminescence images taken indoors.

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].…”

“…A short-pass filter on each LED module transmits the emission of light below 800 nm and a long-pass filter on the camera side transmits the light above 970 nm. This is illustrated in figure 2, which is based on explanations provided in [16,17,25]. The short-pass filter on the LED modules ensures that the light with wavelengths above 800 nm does not reach the cells, at the same time as the long-pass filter on the camera ensures that only light above 970 nm reaches the camera detector.…”

“…The short-pass filter on the LED modules ensures that the light with wavelengths above 800 nm does not reach the cells, at the same time as the long-pass filter on the camera ensures that only light above 970 nm reaches the camera detector. The region between 800 nm and 970 nm is blocked by both filters [16,17,26].…”

“…The LED modules are assembled to allow illumination of one module at a time [16,17,26]. The challenging aspect of using an artificial illumination source to illuminate an area as large as a whole module is the homogeneity of illumination.…”

“…The intensity of illumination affects the intensity of PL emission and therefore the appearance of cells and their defects. This is particularly the case when using a fewer number of LED modules due to weight issues, four instead of eighteen, in case of aerial imaging with a drone [16,17]. Furthermore, the LED modules require powering, which also needs to be taken into account.…”