Snail tracks are grey to black lines that you can see by eye through the front glass. They form where the silver finger paste on the cell front discolours. They run along cell edges and along fine cell cracks that would otherwise be invisible, so they show where the cells are cracked. They usually appear a few months to a year after installation, and they appear faster in summer and in hot climates. The discolouration itself is not known to cause a measurable power loss, but the cell cracks it reveals can lower module power. To check how far the cracking goes, take an EL image of the module. It shows the cracks under the tracks. Do not confuse snail tracks with photobleaching. Photobleaching shows up as clear lines along cracks in encapsulant that has turned brown, which takes several years. Modules with snail tracks tend to show high leakage current in wet leakage tests, so check their insulation as well.
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observed_asc1 drafted · lead Crack pattern in EL image
An EL image of a module with snail tracks shows the cell cracks that the visible tracks follow, along with the cell edges.
sec=6.2.3 h=43e35c4c6150fig=36 h=e875f24bdfb1c2 drafted · lead High wet leakage current
In wet leakage testing, modules with snail tracks tended to show high leakage currents.
sec=6.2.3 h=43e35c4c6150fig=39 h=48fafd3c7c1ec3 drafted · lead Dark metallization discoloration
The silver front-side finger paste turns grey or black at cell edges and along cracks that are normally invisible. This can be seen by eye through the front glass.
sec=6.2.3 h=43e35c4c6150sec=2.2.5 h=d4c58ae820c4tbl=10 h=f95eb9235f8dtime_to_onsetConditions: Earliest typical appearance after module installation. Onset is faster in summer and in hot climates.
sec=6.2.3 h=43e35c4c6150sec=h7 h=8b69da4daaacConditions: Latest typical appearance after module installation. The source gives an onset window of 3 months to 1 year.
sec=6.2.3 h=43e35c4c6150sec=h7 h=8b69da4daaacpresents_as c8