Inactive cell area in EL

In an EL image, an inactive or dead cell area is a part of a cell that stays dark because it no longer adds to the module's power output. It usually shows up next to large cell cracks: thermal stress, mechanical stress and humidity can cut that part of the cell off electrically. A failed cell interconnection can also leave a dark region, because the broken connection no longer collects carriers. In the IR image, the same spot often shows as a hot spot. Take EL images at night or in low light, with DC current driven through the module. Subtracting a dark field image helps cut out stray light. Above about 8 percent inactive area in a typical 60-cell module, power loss rises roughly in line with the inactive area. In a string, the loss rises much more steeply. At half the cell area or more, the bypass diode switches on and about one third of the module's power is lost. Inactive cell parts larger than this can also cause hot spots and burn marks if the active part of the cell has a localized reverse current path. If you image at nominal current, a cell part that looks isolated may not actually cost much power. Imaging at about one tenth of Isc shows more reliably which dark parts matter for power. Check the electrical impact with IV curve tracing, and use IR thermography to look for active heating.

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• sentence 1: support check: partial - Passage defines dead/inactive cell part as no longer contributing to power output, but never says it appears dark in EL images. -->