Electroluminescence (EL) imaging reveals possible solar cell defects such as micro cracks, shunts, busbars contact issues, and more. This type of testing is becoming more and more popular, with most solar panels producers doing as much as 3 different EL tests for each module during production.
The test is done by feeding current from the EL equipment (MAS 2016) to the solar panel, the radiative recombination of carriers causes light emission, as an indirect bandgap semiconductor, most of the recombination in silicon occurs via defects or auger recombination.
Although a comparatively low percentage of the band to band recombination produces the radiative emission, there is still a small quantity of radiative recombination occurring in the silicon and can be detected using an external sensor.
EL testing is a non-destructive and fast measurement way to collect data that is not always visual on the uniformity of solar cells and panels.