Backsheet cracking means any visible damage to the module backsheet, either on its surface or through the whole layer stack, showing up as a crack, burst or scratch. The cracks may be local, such as a burst bubble or a scratch, may follow the cell gaps or busbars, or may cover much or all of the module where the surface has become brittle. Squared cracks under the cell gaps and lengthwise cracks under the busbars point to thermo-mechanical cracking. A cracked backsheet under a hot cell points to temperature-induced damage from a hotspot or burn mark. When cracks are found, check whether all modules with the same bill of materials are affected, because this type usually hits a whole plant once operating time builds up. Deep cracks reduce insulation, especially in wet conditions. Look for insulation faults that keep inverters from starting on dewy mornings. Discoloration or heavy chalking of the backsheet can come before cracking. Deep splits are often followed by moisture getting in and corrosion, more so in hot and humid climates. Optical profilometry and image-based deep learning can find and sort cracks, sometimes before they are visible to the eye.
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observed_asc1 drafted · lead Backsheet surface profile outlier
Optical profilometry with machine learning fits the backsheet surface and flags outliers as cracks, bubbles or delamination, then gives crack width and depth. It can find cracks before they are visible to the eye.
sec=h57 h=6959b882ad79fig=66 h=7e4162410fbec2 drafted · lead Low insulation resistance alarm
When cracks go through the whole backsheet, insulation resistance collapses, especially when wet. Dewy, torn backsheets can cause an insulation fault that stops inverters from starting in the morning, which costs yield.
sec=2.5 h=cdcdc1167476sec=2.5.3 h=eb148eeff8d7review note: support check: partial - Passages support insulation collapse under wet conditions through full-thickness cracks and inverters failing to start in the morning from dewy torn backsheets, but nothing on the specific signals (W, POAI, RH) or an alarm measurement; also the cracks being 'visible' is not tied.
c3 drafted · lead Longitudinal cracks along busbars
Thermo-mechanical type: cracks start at the outer surface and run lengthwise beneath the busbars. They can go through the whole backsheet without any chemical degradation.
fig=51 h=ccf0b7cffcabsec=2.5 h=cdcdc1167476sec=2.5.3 h=eb148eeff8d7c4 drafted · lead Squared cracks between cells
Square cracks under the gaps between cells. They come from acetic acid attack together with thermo-mechanical stress, and the crack runs from the encapsulant side toward the air side.
fig=51 h=ccf0b7cffcabsec=2.5.3 h=eb148eeff8d7review note: support check: partial - Squared cracks under cell gaps with acetic acid attack and crack running encapsulant to air side are stated, but the passage attributes thermo-mechanical stress as a driver generally (figure says thermo-mechanical combined with photo-oxidative); acceptable core but 'together with thermo-mechanical stress' is only loosely tied to the acetic acid mechanism.
presents_as c14