Warm cells near frame

ID: symptom:warm-cells-near-frame
IRI: https://solarlattice.org/kb/symptom/warm-cells-near-frame
Status: active

In IR images of modules running in sunlight, single cells along the bottom frame look warmer than the cells in the upper and middle parts of the module. This pattern, or a patchwork of warm cells, strongly suggests potential induced degradation of the shunting type (PID-s), especially when the affected modules sit near the negative pole of the string. Take the IR images under clear sky with the system running near maximum power, because the pattern disappears at open circuit. If you inject current at night or in the dark, the affected cells look cooler instead of warmer, and EL images show them darker, most clearly at low current bias. Confirm with IV curves: PID-s lowers fill factor, Voc and shunt resistance, and the loss shows up more in low light than at STC. This is different from one clearly hot cell, which points to shading, a defective cell or delamination, and from a partly warm cell, which points to a broken cell or a failed interconnect. Possible remedies include changing the array grounding conditions or recovering the modules with reverse voltage.

<!-- review notes

sentence 4: support check: partial - Cooler IRT and darker EL in the dark are stated, but the low current bias clarity is stated for EL generally, not specifically tied to the injected-current test; the 1/10 bias is mentioned only in u18. -->

Claims

`observed_as`

c1 drafted · lead Warm cells at bottom frame

Seen in IR thermography of operating modules in sunlight near maximum power point; affected cells near the lower frame run warmer than upper and middle cells. Pattern is not detectable at open circuit, and is strongest for modules near the negative (or one) pole of the string.

Review of Failures of Photovoltaic Modules tbl=14.r4 h=7f105cf3f7e6
Review on Infrared and Electroluminescence Imaging for PV Field Applications fig=36 h=78e443f42ff2
Review on Infrared and Electroluminescence Imaging for PV Field Applications sec=2.3.2 h=9b2ddc8cc5ec
Degradation and Failure Modes in New PV Technologies – Annex tbl=15.r1 h=6e2cec50e730
Review on Infrared and Electroluminescence Imaging for PV Field Applications sec=h61 h=e78071080be3

c2 drafted · lead Patchwork pattern in IR image

Alternative PID-s IR signature in which warm cells are scattered across the module in a patchwork.

Review on Infrared and Electroluminescence Imaging for PV Field Applications sec=2.3.2 h=9b2ddc8cc5ec
Degradation and Failure Modes in New PV Technologies – Annex tbl=15.r1 h=6e2cec50e730
Review on Infrared and Electroluminescence Imaging for PV Field Applications sec=h61 h=e78071080be3

review note: support check: partial - Patchwork patterns are named as a PID-s IRT pattern, but 'warm cells scattered across the module' is not described.

c3 verified · fact Cold area in IR image

With current injected in the dark (lab or night-time string test), PID-s affected cells appear cooler than unaffected ones, the reverse of the sunlight pattern.