A hot cell shows up in the IR image as one whole cell that is evenly warmer than its neighbours. This is different from a hot spot, where the heat is concentrated in one small area. It usually comes from cell cracking or shading, which causes a current mismatch and drives the weaker cell into reverse bias, so the cell dissipates power as heat. Take the image during clear, stable weather with high irradiance and the inverter running. Make sure the module has reached steady state, and compare short-circuit, open-circuit and maximum power point load conditions where you can. Cells affected by PID by shunting look warmer in sunlight near maximum power point. They look cooler when current is injected in the dark. Look for warm cells near the bottom frame on modules close to the negative pole of the string. Cell cracks and cell interconnection failures can also show up as heated cells or hot spots in IR images. Hot cells can lead to further damage such as discoloration, delamination, interconnection failures, cell cracks and loss of electrical insulation. Keep moderately heated cells under close watch in regular thermographic inspections, because the temperature difference may grow over time.
<!-- review notes
temperature_riseConditions: IBC half-cell module with built-in Zener bypass behaviour, indoor hot-spot test at 55°C module temperature per IEC 61215-2:2021; rise of hot cell over module temperature
Reported as significantly lower than PERC and SHJ modules under the same test.
sec=2.4.1 h=1046d0084f9fverified by: joshuahamsaverified on: 2026-10-20
c2 verified · fact 10–20 DEG_C
Conditions: Heated cells in field IR inspection classed as unproblematic at the current stage, to be observed in regular thermographic inspections
sec=h58 h=df4b70555c37verified by: joshuahamsaverified on: 2026-10-20review note: possible conflict with c4 (same source; check the conditions)
Conditions: Severe cell defects seen in UAV-based IR mapping of a plant with more than ten thousand modules; such defects correlated strongly with reduced string current
sec=2.1.3 h=73bb98342b5bverified by: joshuahamsaverified on: 2026-10-20review note: possible conflict with c4 (same source; check the conditions)
c4 verified · fact nominal 3 DEG_C
Conditions: Cells located close to the junction box versus the rest of the cell matrix, 2 kWp c-Si installation after 12 years of field exposure
sec=2.1.3 h=73bb98342b5bverified by: joshuahamsaverified on: 2026-10-20review note: possible conflict with c2 (same source; check the conditions); possible conflict with c3 (same source; check the conditions)
produces c3observed_as c1observed_as c2observed_as c1observed_as c1observed_as c1