Snail Trails on The Solar Panels

How are snail trails formed on solar panels?

The formation mechanism of snail trails on solar panels involves a series of complex chemical and physical processes. Firstly, when a chemical reaction occurs on the busbars of the solar panel, it serves as the initial stage for the generation of snail trails. Subsequently, continuous physical stress leads to the formation of microcracks on the surface of the solar panel, creating pathways for moisture to infiltrate. In the presence of an electric field, ultraviolet radiation, and operating temperatures, infiltrated moisture triggers a corrosion process. The deformation of silver contacts and encapsulation foil causes silver particles to migrate onto the EVA foil. The encapsulation polymer contains chemical components such as sulfur, phosphorus, and chlorine, leading to secondary chemical reactions with silver. The accumulation of these tiny particles, formed through multiple reactions, eventually creates the distinctive snail trails on the surface of the solar cells and encapsulation materials.

When solar panels are exposed to harsh outdoor conditions for an extended period, the EVA material begins to degrade, releasing carbon dioxide and acetic acid. In the presence of oxygen, carbon dioxide reacts with the silver paste used as a conductive material in the solar panel, forming silver carbonate:

4Ag + 2CO2 + O2 —> 2Ag2CO3

Subsequently, silver carbonate reacts with acetic acid in the EVA material, forming silver acetate:

Ag2CO3 + CH3COOH—> CH3COO(Ag) + CO2 + H2O

Silver acetate then deposits onto the EVA and manifests as brown lines (snail trails).

It is crucial to note that microcracks are a prerequisite for their formation. If the internal components of the solar panel are not influenced by outdoor elements, especially if moisture cannot infiltrate, the occurrence of snail trails becomes highly improbable. In this process, the presence of microcracks becomes a critical factor, providing the necessary conditions for the appearance of snail trails.

The Key Reasons Behind The Formation of Snail Trails on solar panels?

Snail trails emerge after prolonged exposure of solar modules to outdoor elements, prompting the question of their precise origin. According to findings from this study, the root cause of snail trails can be attributed to material defects and the initiation of chemical processes.

1. Differences in chemical properties between EVA (ethylene vinyl acetate) foil and silver contacts.

2. The degree of degradation of the EVA material, i.e. how it ages and wears.

3.The water vapor permeability of the solar panel backsheet material, i.e. whether it can effectively prevent water vapor from penetrating into the interior of the solar panel.

Many of these material defects manifest while solar panels are actively generating electricity on-site, though occurrences during the manufacturing process are not uncommon and are referred to as ‘manufacturing cosmetic blemishes.’

The induced chemical processes are a consequence of the material defects. Predominantly, corrosion reactions are the prevailing induced reactions leading to the formation of snail trails. These trails manifest when microcracks appear on the solar panel surface, providing a pathway for moisture and oxygen infiltration. While not every microcrack results in adjacent snail trails, there is a notable likelihood of finding these two defects coexisting in the same location on a solar cell. Consequently, it can be broadly asserted that microcracks stand out as the primary instigator of snail trails on solar panels.