Why do You See Snail Trails on the Surface of Solar Panels?

Solar panels will show snail trails after prolonged exposure to outdoor elements.

It is a type of defect that occurs when there’re existing physical defects on the solar panels, such as microcracks, that create a pathway for undesirable chemical reactions in the solar cells.

Snail trails are a common yet overlooked solar panel defect. While generally snail trails are no big cause for alarm, they always indicate other defects such as microcracks on your modules thus, they must not be ignored.

If you have noticed brown discoloration lines (snail trails) on your solar panels, you might want to find out what they are, their causes, and how to prevent them.

Throughout this article, we'll discuss everything you need to know about solar panel snail trails.

What are Solar Panel Snail Trails?

Snail trails, also known as snail tracks or worm marks are lines of local discoloration that occur on solar panels after a long usage time.

Usually, these lines appear dark or brown and occur near busbars, on solar edges, or close to microcracks.

These small brown lines give the illusion that snails or worms have passed over the solar panels, hence the origin of the name snail trails/worm marks. Snail trails can have a large visual impact if they’re all over the solar panel.

Usually, when a solar panel is defective i.e. it has microcracks, the snail trails will appear after months of exposure of the modules to outdoor elements. Thereafter, the snail trails will remain constant and visible on the solar panels.

It is almost certain that there are other defects present on your solar panels, primarily microcracks if snail trails are visible.

Snail trails don't discolor the solar cell surface itself. Rather, they discolor the grid fingers of the same cell at the same position, causing it to look like a continuous brownish line.

Snail trails on solar panels are easily transferable to the encapsulation foil. When you disassemble solar panels with the snail trail defects, you’ll most likely find imprints of the discoloration lines on the module's encapsulation foil.

We now have a rough idea of what solar panel snail trails are, but how exactly do they occur?

Snail Trails: How are they Formed?

Snail trails occur when a chemical reaction occurs on the grid finger of a solar panel.

Usually, the product of the chemical reaction is organic particles that form a film on the silver surface. The film appears as the continuous brownish lines on the surface of the solar panel.

The same organic particles are transferred to the EVA foils causing brownish imprints on this solar panel component too.

Now you may ask, what is the composition of the organic particles forming the snail trails?

According to this snail trails root cause analysis study, the organic particles making up the snail trails are comprised of 5 main elements:

  • Silver
  • Sulfur
  • Phosphorus
  • Carbon
  • Chlorine

The same study proposes this model of snail trails formation:

  1. Microcracks form on the surface of a solar panel after continuous physical stress, which allows moisture to find its way into the solar cells.
  2. In the presence of electrical fields, UV radiation, and operation temperatures, the infiltrated moisture induces corrosion.
  3. The silver contact and encapsulation foil are distorted, causing silver particles to migrate to the EVA foil.
  4. Encapsulation polymers contain chemical components such as sulfur, phosphorus, and chlorine, so secondary chemical reactions occur between silver and these chemical components.
  5. The secondary reactions add up to the particles that form these snail trails on both the surface of the solar cells and the encapsulation material.

Researchers have drawn other elaborate models explaining how snail trails occur.

One that relates to the above findings involves the formation of silver acetate as the snail trail’s main component:

  • On long exposure of solar panels to harsh outdoor conditions, the EVA material starts to degrade and releases carbon dioxide and acetic acid.
  • In the presence of oxygen, carbon dioxide first reacts with the Ag from the Ag paste used as the conductive material in solar panels forming silver carbonate.

4Ag + 2CO2 + O2 —> 2Ag2CO3

  • The silver carbonate then reacts with acetic acid from the EVA material to form silver acetate.

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

  • The silver acetate is then deposited on the EVA and appears as the brownish lines (snail trails).

Note: These proposed models of the formation of snail trails on solar panels suggest that microcracks are a prerequisite condition.

It is highly unlikely that snail trails will appear if outdoor elements like moisture don’t find their way into the inner components of solar panels.

What Causes Snail Trails on Solar Panels?

Snail trails occur after prolonged exposure of modules to outdoor elements. But what is exactly the root cause?

According to this study, the root cause of snail trails is material defects and induced chemical processes.

Common material related factors include:

  • The difference in chemical properties of EVA foils and the silver contacts
  • The degradation extent of the EVA material
  • Water vapor permeability of the solar panel’s backsheet material

Most of these material defects arise while solar panels are on site producing electricity.

However, they can still occur during the manufacturing process. Snail trails due to defects in the manufacturing of solar panels are also known as ‘manufacturing cosmetic blemishes’.

The induced chemical processes follow the material defects. Primarily, corrosion reactions are the most common induced reactions that lead to the formation of snail trails.

They’ll occur when microcracks are present on the surface of the solar panel, creating a way for moisture and oxygen to seep in.

Although not all microcracks have snail trails near them, there’s a high chance these two defects will be found in the same spot on a solar cell.

So, in general, we can say that microcracks are the leading cause of snail trails on solar panels.

Effects of Snail Trails on Solar Panels

Reduced aesthetic appeal of solar panels

The look of solar panels matters if they’re installed in a common sight area, such as the roof facing the main entrance to your property.

Solar panels with these brownish tracks degrade the aesthetic appeal of solar panels and the surface they’re installed on.

With the deterioration of snail trails with time, the associated reduced aesthetic appeal can also worsen. If you value the aesthetic value of your home, then you should consider replacing the deteriorated solar panels.

The good news is, people looking to invest in solar on a budget are always looking for these modules.

Reduced power production efficiency

According to this investigation done on crystalline solar panels with snail trails, the power production efficiency of these modules could be up to 9.1 % lower than that of common solar panels.

The efficiency reduction, however, is mainly due to microcracks that appear before the snail trails.

In other words, even if today your solar panels show snail trails, it’s more likely their power output has been below average for quite some time.

Formation of hotspots

Snail trails cause resistance to the flow of current (local shunts) in solar panels, which results in hotspots and a reduction in solar panel efficiency.

The effect is even worse if the snail tracks occur near micro-cracks.

The amount of energy lost as heat also depends on the depth of the cracks. In this regard, it’s essential to keep track of the performance of your solar panels so that you know the right time to replace them.

How to Prevent the Formation of Snail Trails on Solar Panels?

Develop better polymer material combinations for EVA

Making a solar panel with certain polymer materials can cause snail trails to form or worsen those already formed.

To determine the best polymer material combination to use in solar panels, it is necessary to perform sufficient chemical and physical characterization. Only materials that don't cause the formation of snail trails should be used in solar panels.

Optimize the amount of phosphorus used in solar panels

Solar panels use antioxidants and stabilizers containing phosphorus.

Considering that phosphorus is one of the chemical components that increase the formation of organic particles making up snail trails, it can help if the usage of this chemical component is optimized in solar panels.

Research can also be done to come up with alternatives that are as good as phosphorus.

Handle solar panels carefully to prevent micro-cracks from forming

As mentioned earlier, micro-cracks on solar panels are the main cause of snail trails.

You'll find microcracks on your solar panels if there’re physical stresses during transport, installation, or when the modules are installed and producing power.

Proper handling of modules eliminates the risk of this physical defect as well as the snail trails.

Frequently Asked Questions about Snail Trails on Solar Panels

Will a solar panel work if it has snail trails?

Solar panels with snail trails will still convert sunlight to electricity, but their power production efficiency will fall significantly.

It can be up to 10% lower than solar panels with no snail trails and related problems such as microcracks.

Of course, the extent of snail trails on a solar panel will determine how much efficiency is affected.

Solar panels with snail tracks also have microcracks that contribute greatly to their reduced performance.

Are all brown spots on solar panels snail trails?

Browning of sections of a solar panel isn’t always a sign of snail trails.

Any uncontrolled chemical reaction between the chemicals on the surface of the solar panels and the chemical components making up the module can cause solar panels to brown.

Even the snail trails themselves can be colored differently depending on the reaction involved. So, not all brown spots on solar panels are snail trails, and not all snail trails on solar panels are brown.

What is snail trail contamination in solar panels?

Snail trail contamination is the discoloration of solar panels due to corrosion reactions happening on the grid fingers or edges of a solar panel.

This solar panel defect has been observed on defective modules since 2012. Defective materials used in modules and aging issues such as microcracks are the main reasons for solar panels snail trail contamination.

Material improvements and proper maintenance of solar panels can prevent snail trail contamination from occurring.

Would real snail trails affect the performance of solar panels?

If many snails infest your solar panels, they may leave heavy slime trails on them, causing significant shading. Heavy slime coverage on solar panels can cause substantial shading.

With shading, the modules are blocked off from sunlight; hence their productivity is reduced.

In spite of this, it is unlikely that many snails will get to your solar panels and spread slime to shade them.

Is it worth it to invest in used solar panels with snail trails?

If you are on a tight budget, you can invest in solar panels with snail trails to increase your off-grid solar power production.

Usually, these modules will cost you way less than new ones and can save you quite some money.

However, you need to ensure that their productivity is still within the accepted standard range.

If you want to produce as much clean, renewable energy as possible and don't have an issue with the upfront costs, then new solar panels would be a better investment.


Like the usual snail tracks, snail trails on solar panels are dark continuous lines that occur on the edge of the solar cells or near microcracks formed after corrosion chemical reactions occur due to moisture infiltration into the solar cells.

Material factors form a prerequisite for the formation of solar panel snail trails, but you’ll most likely see this defect when your solar panels have been exposed to outdoor elements for an extended period.

Since prolonged exposure of solar panels to outdoor elements is inevitable, the ultimate solution for snail tracks lies in the hands of manufacturers.

Solar panel manufacturers should develop better polymer material combinations that are less likely to contribute to the formation of snail trails and related problems such as microcracks.