Solar Lattice

Symptom

Uneven cell heating

ID
symptom:uneven-cell-heating
IRI
https://solarlattice.org/kb/symptom/uneven-cell-heating
Status
active
Also known as
inhomogeneous heating, Heated cells, overheated cells

Uneven cell heating is seen in an IR image of a module under load: some cells, or parts of cells, are warmer than the cells around them. A bypass diode that has failed short-circuited makes individual cells heat unevenly during operation. It also keeps the module's voltage and power low all the time. When one whole cell is warmer, the cause may be shading, a defective cell or a delaminated cell. Look at the module first, because a leaf or lichen can cause a loss that clears after cleaning. When only part of a cell is warmer, suspect a broken cell or a disconnected interconnect. This usually comes with a large power loss and a lower fill factor on the IV curve. Heating at a single point usually points to partial shading such as bird droppings. A close visual inspection can then reveal a cell crack. Shading or cracking can drive a cell into reverse bias, so that it dissipates power as heat. Monocrystalline hot cells heat evenly across the cell, while multicrystalline hotspots stay local. Temperature differences of 10 to 20°C between cells are not a problem yet, but they may grow. Check such modules again in regular IR inspections.

<!-- review notes

Claims

observed_as

c1 verified · fact Hot cell in IR image

One cell is clearly warmer than its neighbours. Possible causes are shading, a defective cell or a delaminated cell. In monocrystalline cells the hot cell effect raises the temperature evenly across the whole cell.

verified by: review-workflowverified on: 2026-10-20review note: support check: partial - One warmer cell, causes (shading, defect, delaminated) and the monocrystalline homogeneous heating are stated, but the TmpBOM signal pattern is not in the passages (not judged), and 'hot cell effect' is described as associated with mono cells generally.

c2 drafted · lead Localized IR hotspot

Heating at a point. Possible causes are partial shading (for example a bird dropping or a lightning rod), local junction breakdown, which is mainly seen in multicrystalline cells, or a micro-arc in the interconnection circuit.

c3 drafted · lead Partly heated cell in IR

Part of one cell is warmer than the rest. This is linked to a broken cell or a disconnected string interconnect, and comes with a drastic power loss and a lower fill factor.

temperature_rise

c4 drafted · lead 10–20 K

Conditions: Temperature gradients between heated cells seen in field IR inspection. The source calls this range unproblematic for now but says it may grow during operation.

c5 drafted · lead ≤ 25 K

Conditions: Hot cell temperature above module temperature for an IBC half-cell module in an indoor hot-spot test at 55°C module temperature (IEC 61215-2:2021).

Referenced by

Data