Backsheet chalking happens when the polymer in the outer backsheet layer breaks down under light and heat and releases its inorganic pigment or filler. The usual root cause is an outer layer that does not withstand weathering well enough, for example one without UV stabilisation. You will see a white powder on the rear surface that comes off on a finger, and the backsheet usually looks rough or dull. Confirm it by visual inspection and a simple wipe test on the backsheet. Chalking does not affect safety or performance at first, but it can signal ongoing backsheet degradation and can come before cracking, insulation failures or moisture-driven corrosion. Chalking does not reliably predict cracking, because cracking has been seen both with and without chalking. Inspect affected modules regularly to track progress, and keep ground fault detection active at all times. To prevent it, check that the IEC 61215 certification and the bill of materials are valid.
affectsAffects the outer polymer layer of the backsheet, which contains inorganic pigment or filler.
sec=h61 h=644a3733bb6btbl=11.r1 h=ce4fb0199cddsec=2.5.1 h=4dfb46bec383caused_byc2 drafted · lead Low-quality material
The root cause is an outer layer that does not resist weathering well enough, for example missing UV stabilisation. Examples given are PA or PO outer layers.
sec=2.5.1 h=4dfb46bec383review note: support check: partial - Passage gives root cause as insufficient weathering stability (lack of UV stabilisation, PA/PO) but does not name it 'low-quality material' in the chalking context; close but a mapping inference.
presents_asc3 drafted · lead White surface powder
A white powder sits on the outer backsheet surface. It comes off on a finger and can be removed.
sec=h61 h=644a3733bb6btbl=11.r1 h=ce4fb0199cddc4 drafted · lead Dull or rough surface
A chalked backsheet usually looks rough or dull.
sec=h61 h=644a3733bb6btbl=11.r1 h=ce4fb0199cdddetected_byc5 drafted · lead Visual inspection
tbl=11.r2 h=00041690913dsec=h61 h=644a3733bb6btbl=8 h=88163ae58405c6 drafted · lead Tactile inspection
Run a finger over the backsheet or do a simple wipe test to check for powder.
sec=h61 h=644a3733bb6btbl=11.r1 h=ce4fb0199cddsec=2.5.1 h=4dfb46bec383leads_toc7 drafted · lead Backsheet Cracking
Chalking can be a precursor to cracking, but this cannot be predicted. Cracking has been seen with and without chalking, and PVDF backsheets usually crack without chalking.
tbl=11.r5 h=893e30a4726dsec=h61 h=644a3733bb6btbl=30.r3 h=0950ed925bf5tbl=10.r3 h=8121b95d9f56sec=2.5.1 h=4dfb46bec383c8 drafted · lead Severe Metallization Corrosion
More moisture diffusing into the encapsulant and active parts can corrode cells and connectors, which reduces performance.
tbl=11.r5 h=893e30a4726dsec=h61 h=644a3733bb6breview note: support check: partial - Moisture diffusion leading to corrosion of cells and connectors is stated, but 'severe metallization corrosion' as such is not named and chalking is only indirectly linked via reduced UV protection.
mitigated_byc9 drafted · lead Close monitoring
Use regular inspections to track how the chalking progresses.
sec=h61 h=644a3733bb6btbl=11.r8 h=d4da399f6da7c10 drafted · lead Continuous ground fault detection
The inverter or other devices should provide ground fault detection at all times.
sec=h61 h=644a3733bb6btbl=11.r8 h=d4da399f6da7c11 drafted · lead Certified product selection
Check that the IEC 61215 certification is valid.
sec=h61 h=644a3733bb6btbl=11.r8 h=d4da399f6da7c12 verified · fact Bill of materials verification
sec=h61 h=644a3733bb6btbl=11.r8 h=d4da399f6da7verified by: joshuahamsaverified on: 2026-10-20
c13 drafted · lead Accelerated weathering screening
As a preventive step, backsheets can go through accelerated weathering tests followed by wipe tests.
sec=2.5.1 h=4dfb46bec383caused_by c13distinguished_from c19