Snails trails occur in correspondence with microcracks in the cells, consisting of a discoloration on the surface of the solar panels. The process occurs in the presence of heat, UV radiation and humidity.

Why do snail slime appear on solar panels?

After several months of outdoor exposure, snail marks will begin to appear on defective PV modules. Normally, except for new breaks caused in the module, the snail print remains stable after a couple of months. 

In many cases, along with the rupture, a localized drift phenomenon is generated which develops heat and gives the possibility for small amounts of moisture to reach the cell surface.

The contact silver of the grid can become dissolved and the migration of silver ions to the EVA (Ethyl Vinyl Acetate) foil can lead to the formation of a snail slime trail, mainly of silver nano-particles showing a typical brown color.

The discoloration appearing on the snail slime occurs due to the formation of silver acetate, which is synthesized by silver carbonate (Ag2CO3) originating from the reaction of Ag ions and carbon dioxide and acetic acid that originates from the degradation of the EVA encapsulation. The effect of this reaction is that it can reach the front side of the panel from the back side and causes a chemical decomposition on the front side of the panel.

Not all types of breaks will generate this moisture, the intensity of which depends on both the encapsulation material and the screen printing material.

In addition, it also depends on the depth of the crack, thus on the amount of energy involved and the amount of power that is locally transformed into heat.

What effect do snail slime have on solar panels?

The mere existence of snail slime by itself does not affect energy generation. However, it is noted that they often appear when there are microcracks running through the cells that can affect energy generation.

If we focus exclusively on the optical effect, this problem does not significantly compromise the performance of the PV module, the apparent yellowing of the EVA does not reduce the power output.

On the other hand, on the other hand, where you see a snail print, there is probably a more or less significantly cracked cell. This crack may be associated with a degradation of the production capacity. However, not all cracks have to cause a deactivation of a significant area of the cell.

To ensure the production and condition of the solar panel, electroluminescence and IV tests remain in any case essential to quantify the effective extent of the consequences of degradation caused by a broken cell.