This signature is a short-circuit current on the IV curve that is lower than expected. The expected value can come from the cell area, technology and layout, from the label or flash report, or from an earlier curve measured under comparable conditions. Isc mainly reflects optical influences, so a low Isc points to light not reaching the cells, and the effect resembles a reduction in irradiance. Typical causes are loss of encapsulant transparency from yellowing or browning, glass corrosion, and delamination that optically uncouples the layers. Uniform cases lower Isc and Pmax only. Non-uniform cases also give a sloped region near Isc and steps in the curve. Severe metallization corrosion lowers Isc together with fill factor, because series resistance rises. Light-induced degradation lowers Isc, fill factor and Voc. In bifacial PERC and TOPCon modules affected by PID-p, STC IV curves have shown a significant drop in Isc but no noticeable drop in shunt resistance. String Isc can be taken from an IV curve trace on an isolated string. Before reading a deviation as a fault, check for measurement errors, instrument set-up problems, wrongly entered module data, shading and soiling.
<!-- review notes
Monitoring channels where this signature appears, named by SunSpec model point.
| Point | Unit | Pattern |
|---|---|---|
model_160.DCA | A | slow, long-term decline in irradiance-normalized string current |
model_502.A | A | affected modules show lower current than neighbours at the same irradiance |
model_403.InDCA | A | affected string current below peer strings |
typical_power_lossc1 verified · fact ≤ 4 PERCENT
Conditions: Power loss from delamination, one of the failures that lowers Isc; reported as a limited-loss failure
Applies to fm:delamination
sec=5.2.4 h=9ce8dc98ece9verified by: review-workflowverified on: 2026-10-20
c2 verified · fact ≤ 3 PERCENT
Conditions: Power loss from glass corrosion, one of the failures that lowers Isc
Applies to fm:glass-corrosion-abrasion
sec=5.2.4 h=9ce8dc98ece9verified by: review-workflowverified on: 2026-10-20
observed_as c2observed_as c5observed_as c2observed_as c2observed_as c3observed_as c1