A module hotspot is a cell or substring that runs much hotter than the rest of the module while it is producing power. Common causes are cracked cells, solder bond defects, shadows from soiling, bypass diode behavior, or mismatch that pushes part of the module into reverse bias. It can reduce string output, and the risk grows if cracked cells or bypass diodes are left in service. Find it with a drone infrared scan in clear, stable conditions with the inverter running, comparing the module with its neighbours in the same string. Treat one thermal image as a screening result only, then confirm with string current, IV curve shape and a visual check before approving replacement. Raise the priority if the anomaly repeats across inspections or several modules in the same string show similar signatures. Isolate the string, check the heat signature under load, replace the module if cell damage is confirmed, and retest string current afterwards. If left in place, severe heating can lead to discoloration, delamination, interconnection and solder failures, backsheet damage and broken glass.
caused_byc1 verified · fact Cell Cracks
Cracked cells can cause current mismatch and reverse bias, so the cell dissipates power as heat.
sec=h4 h=a46a7d318434sec=2.4.1 h=1046d0084f9fverified by: joshuahamsaverified on: 2026-10-16
c2 drafted · lead Partial shading
Includes shadows from soiling.
sec=h4 h=a46a7d318434sec=2.4.1 h=1046d0084f9fc3 drafted · lead Solder bond defect
sec=h4 h=a46a7d318434c4 drafted · lead Cell current mismatch
sec=h4 h=a46a7d318434sec=2.4.1 h=1046d0084f9fc5 drafted · lead Cell reverse bias
Mismatch drives part of the module into reverse bias, where the underperforming cell heats up.
sec=h4 h=a46a7d318434sec=2.4.1 h=1046d0084f9faffectsc6 drafted · lead Solar cell
sec=h4 h=a46a7d318434sec=2.4.1 h=1046d0084f9fpresents_asc7 drafted · lead Hotspot in IR image
Individual cells or substrings run locally hot while the module is under load.
sec=h4 h=a46a7d318434review note: support check: partial - Localized high-temperature cells/substrings under load are stated, but IR imaging as the presentation is only implied by the drone IR detection method.
c8 verified · fact Reduced string current
sec=front h=52a281766501sec=h2 h=f89fa075e5e7verified by: joshuahamsaverified on: 2026-10-16
detected_byc9 verified · fact Infrared thermography
Drone IR scan in clear, stable conditions with the inverter running and enough irradiance; compare against adjacent modules in the same string. Treat it as screening only.
sec=front h=52a281766501sec=h2 h=f89fa075e5e7sec=h5 h=dbed0f83b34dverified by: joshuahamsaverified on: 2026-10-16review note: support check: partial - Drone IR scan conditions and neighbour comparison are stated, and the screening-only note appears in the notes, but the evidence cited for it is limited to u6 which is not listed here.
c10 verified · fact IV curve tracing
sec=front h=52a281766501sec=h2 h=f89fa075e5e7sec=h5 h=dbed0f83b34dverified by: joshuahamsaverified on: 2026-10-16
c11 drafted · lead Visual inspection
sec=front h=52a281766501sec=h2 h=f89fa075e5e7sec=h5 h=dbed0f83b34dc12 drafted · lead String current measurement
sec=h5 h=dbed0f83b34dmitigated_byc13 drafted · lead String isolation
sec=front h=52a281766501sec=h2 h=f89fa075e5e7c14 drafted · lead Module replacement
Replace only once cell damage is confirmed and the electrical impact and repeatability have been checked.
sec=front h=52a281766501sec=h2 h=f89fa075e5e7sec=h6 h=4629f9b5656ec15 verified · fact Post-repair verification
Retest the string current after the repair.
sec=front h=52a281766501sec=h2 h=f89fa075e5e7verified by: joshuahamsaverified on: 2026-10-16
c16 verified · fact Bypass diode integration
Caps the power the shaded cell dissipates but does not remove the effects of hot cells.
sec=2.4.1 h=1046d0084f9fverified by: joshuahamsaverified on: 2026-10-16
c17 verified · fact Cell current binning
sec=2.4.1 h=1046d0084f9fverified by: joshuahamsaverified on: 2026-10-16
c18 verified · fact Cell shunt resistance screening
sec=2.4.1 h=1046d0084f9fverified by: joshuahamsaverified on: 2026-10-16
c19 verified · fact Shade-resistant module design
For example half-cell, shingled, or per-cell diode modules; fewer cells per bypass diode also lowers hot cell temperature.
sec=2.4.1 h=1046d0084f9fverified by: joshuahamsaverified on: 2026-10-16
leads_toc20 drafted · lead Cell Interconnection Failure
Includes solder joint failure if the cell temperature goes past the solder melting point.
sec=2.4.1 h=1046d0084f9fc21 drafted · lead Cell Cracks
sec=2.4.1 h=1046d0084f9fc22 drafted · lead Glass Breakage
Caused by a high temperature gradient, observed for example in non-tempered glass.
fig=66 h=fc43cc44285esec=2.4.1 h=1046d0084f9freview note: support check: partial - Glass breakage risk from high cell temperatures and thin-film hot-spot glass breakage via temperature gradient in non-tempered glass are stated, but not specifically for this cause's cell damage hot spot.
c23 verified · fact Delamination
sec=2.4.1 h=1046d0084f9fverified by: joshuahamsaverified on: 2026-10-16
c24 drafted · lead Discoloration
sec=2.4.1 h=1046d0084f9fc25 drafted · lead Loss of electrical insulation
sec=2.4.1 h=1046d0084f9fc26 drafted · lead Backsheet bubbling and deformation
Reported for temperatures above 170°C.
sec=2.4.1 h=1046d0084f9fc27 verified · fact Junction Box Failure
In extreme cases the junction box may detach.
sec=2.4.1 h=1046d0084f9fverified by: joshuahamsaverified on: 2026-10-16
distinguished_fromc28 drafted · lead Hot cell — told apart by Infrared thermography
A hot spot is a localized heat point (local junction breakdown), mainly in multicrystalline cells. A hot cell heats evenly across the whole cell area, mainly in monocrystalline cells.
sec=2.4.1 h=1046d0084f9freview note: support check: partial - The hot spot versus hot cell distinction is stated, but using IR thermography to tell them apart is not stated.
temperature_riseConditions: Hot cell in an IBC half-cell module relative to module temperature, indoor hot-spot test at 55°C module temperature per IEC 61215-2:2021
sec=2.4.1 h=1046d0084f9frelated_to c4caused_by c12caused_by c12leads_to c33leads_to c26leads_to c26distinguished_from c10leads_to c10leads_to c19