What are the dark lines or snail trails appearing on my panels?

What you will see

• Grey or dark lines following parts of a solar cell.
• Similar markings on several panels.
• A pattern that becomes more noticeable in particular light.
• Visible marks without an obvious change in the app’s total output.
• Other marks can look similar from a distance. Avoid assigning a diagnosis before the module has been properly assessed.

Why it happens

IEA PVPS describes snail tracks as discolouration associated with cell metallisation, often following cell edges or cracks. Their appearance does not directly quantify a panel’s power loss. The assessment needs to distinguish the visible discolouration from any underlying cell damage.

If further investigation is justified, specialist imaging and electrical assessment can provide information that ordinary photographs cannot. The installer or manufacturer should decide which evidence is appropriate for the particular complaint.

Keep the discussion focused on what has changed, which modules appear affected and whether performance records show a corresponding change. Do not assume that one marked module proves that every panel in the array has the same condition.

Diagram

Looks versus performance

What you can see

Lines along cell edges or cracks, in certain light.

What decides action

Performance records, which modules, and specialist imaging if needed.

The marks may be inside the module. Do not scrape, polish or apply chemicals.

What you can check yourself

• Save photographs taken from an already safe location.
• Note when the marks were first noticed.
• Identify the approximate affected area using an existing layout.
• Gather panel model and serial records from the handover file.
• Preserve production history and earlier inspection photographs.
• Tell us if there is no safe way to photograph the marks. Access can be planned as part of the inspection.

What not to do

• Do not scrape, polish or apply chemicals to remove lines that may be inside the module. Do not press on the glass, walk on panels or dismantle a module. Avoid treating online photographs as a warranty decision for your equipment.

When to call us

• Arrange an assessment of new or spreading marks, especially when accompanied by warnings, visible damage or a persistent production change.

Panel marks in Faisalabad and Lahore

Send our Faisalabad or Lahore team dated photos and serial records. We will link what you see to your performance data.

Send us

Available photographs, panel identification records, the date first noticed, production history, and your city and area.