Electroluminescence (EL) Testing for solar modules
Electroluminescence (EL) imaging is used by SunPower to test every one of their manufactured solar panels for cell inherent defects. The example above is from a SunPower 170W flex panel and shows a good panel. EL imaging is becoming more and more important for quality testing of solar cells, as the defects can be severe but are not always visible to the naked eye. With the aid of this technology checks can be thorough and done quickly. Some examples of what they are looking for include:
micro cracks, debris, bad soldering on the busbar, short circuit
Here's a few photos of what a 'bad' panel might look like under the EL test, rest assured these would not have made it past the factory floor.
Rest assured the SunPower panels that make their way to you as a customer are built to a very high standard and SunPower has very low rates of bad panels and warranty replacements.