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  • Writer's pictureSarah Lozanova

Common Solar Panel Defects: How To Identify Sources Of Panel Underperformance

Solar project underperformance is a growing issue for solar energy system owners. According to Raptor Maps data from analyzing 24.5 GW of large-scale solar systems in 2022, underperformance from anomalies nearly doubled from 2019 to 2022, from 1.61% to 3.13%. Solar panel underperformance from equipment-related downtime and anomalies is increasingly common as systems age.

Unfortunately, these issues have a substantial financial cost. The estimated annual revenue loss from the 24.5 GW from the study sample was $82 million, indicating a $2.5 billion loss for the entire solar energy industry. In addition, there are numerous other risks that could hinder solar system performance, according to the 2023 Solar Risk Assessment. Extreme weather risks, more solar systems in harsh weather environments, and the difficulty of predicting equipment-related performance are important factors.

Thus, solar power professionals need to be knowledgeable about solar energy output issues to better service solar clients and prevent underperforming solar assets. Regular maintenance and performance modeling can help prevent revenue loss for solar system owners through early detection and corrective action. Let’s examine how to know if a solar project has a performance issue, as well as common solar panel defects, and how to resolve them.

How To Tell If Solar Panels Are Underperforming

There are several tell-tale signs from reviewing solar monitoring data or visual inspections that solar panels are underperforming. A significant drop in energy production compared to the PV system's rated capacity clearly indicates underperformance. Monitor solar energy production regularly and compare it with the expected output.

Keep in mind, however, that atypically hot or cloudy weather can also cause temporary underperformance issues, as excessive heat or cloud cover can reduce solar panel production. In this case, no corrective action is needed – just patience.

Dust, dirt, or debris accumulation on the panels can reduce efficiency. Similarly, shading from nearby trees or buildings can cast shadows on the panels and hinder their performance. Cracks, chips, or other visible damage on the panels' surface can affect their ability to convert sunlight into electricity. Likewise, electrical problems with the system, such as loose connections, faulty inverters, or malfunctioning wiring, can lead to reduced performance.

Identifying Common Solar Panel Defects In Your Installations

There are a variety of equipment anomalies that result in lower power generation caused from poor soldering, lamination quality, cell design, quality control, frame or glass construction, busbar corrosion, and junction box defects. Proactively addressing such issues from routine maintenance, inspection, and reviewing solar monitoring data can help mitigate issues. Read on to learn about some of the most common problems with solar power panels that can impact their lifespan.

Snail Trails

Snail trails are a type of defect that appears as dark or discolored patterns on the surface of solar panels and can be seen with the naked eye. They are caused by a chemical reaction within the panel's encapsulation material caused by moisture and oxygen. Over time, this reaction can lead to the formation of conductive pathways, reducing the panel's overall efficiency.

To spot snail trails, inspect the surface of the panels regularly for any visible dark streaks or discoloration. Snail trails are more noticeable under certain lighting conditions, such as direct sunlight.

There is no practical way to repair snail trails, but they do not necessarily always impact solar panel performance. If the panels are under warranty, you may contact the manufacturer for a potential replacement or determine if the snail trails impact solar electricity output.


Hotspots occur when specific cells within a solar panel become overheated due to localized shading, dirt, or manufacturing defects. These hotspots can lead to irreversible damage to the affected cells and reduce the overall output of the panel.

To identify hotspots, use thermal imaging during the day when the panels are under full sunlight. Hotspots will appear as areas with significantly higher temperatures than the rest of the panel.

Ensure that the panels are not shaded by nearby objects or covered with dirt or debris. Therefore, it can be helpful to clean solar panels regularly in certain climates or locations impacted by debris. If a malfunctioning cell is causing the hotspot, consider replacing the affected panel.

Shading And Shadowing

Shading and shadowing are common issues that can severely impact solar panel performance. Even partial shading on a single cell can cause a significant reduction in the energy output of the entire panel.

Inspect the panels periodically during the day to spot shading and shadowing issues, especially when the sun is at a low angle. Look for objects, nearby structures, or vegetation casting shadows on the panels. Homeowners and business owners can monitor this as they’re around the panels more frequently; make sure they know to call their installer if they notice excessive shading or shadowing. Additionally, analyze the system's monitoring data for any unusual drops in energy production.

To address shading problems, consider advising trimming or removing nearby trees or objects that cause shading. Alternatively, you can use microinverters or power optimizers that mitigate the impact of partial shading on the entire system.


Microcracks, also known as microfractures, are tiny cracks in photovoltaic cells. This type of solar degradation is often caused by mechanical stress during installation, transportation, or environmental factors like temperature fluctuations. These microcracks can cause reduced panel performance.

To spot microcracks, visually inspect the panel's surface under proper lighting – cracks may appear as faint lines on the cells or the surrounding material. Also, you can use electroluminescence crack detection (ELCD) testing, a method that identifies microcracks that may not be detected from a visual inspection.

If the microfractures are minor and do not significantly affect the panel's performance, they can be left as is. However, it's best to contact the module manufacturer for possible warranty claims if they are severe and impact output. Otherwise, consider replacing the affected panel to maintain the system's overall efficiency.


Delamination in PV panels is a serious issue that occurs when the layers of materials within the PV module separate or become detached. It can happen due to moisture entering the backsheet via cracks and can lead to a reduction in the panel's efficiency and busbar corrosion.

To identify delamination, conduct a thorough visual inspection of the solar panels. Look for any signs of bubbles, blisters, or separations between the layers of the panel, or discoloration or dark spots on the panel's surface. Also, electroluminescence (EL) testing can reveal delamination, by capturing images of the panel in the dark.

To address delamination when the solar panels are still under warranty, contact the manufacturer to report the issue. Delamination is often covered under standard warranties, and the manufacturer may provide replacement solar modules. If the delamination is severe and negatively affecting the panel's performance, it's best to replace the affected panels with new ones to ensure optimal energy production. However, beware that lamination can increase the likelihood of electrical shock, potentially creating a safety issue. If the solar system is reaching the end of its lifespan, it might be better to decommission it instead of replacing faulty panels.

Potential Induced Degradation (PID)

Potential Induced Degradation (PID) is a phenomenon that affects the performance of solar panels due to a high voltage potential difference between the solar cells and the frame, glass, or mount. This potential difference can lead to a degradation of the solar cells, resulting in reduced energy output.

To spot PID, monitor the solar panel's performance regularly and look for signs of decreased efficiency. Some symptoms of PID include a rapid decline in energy production or a significant drop in performance during high humidity and high-temperature conditions.

To address PID in solar panels, consider using PID reversal equipment. Properly grounding the system and using string inverters or module-level power electronics can also help mitigate PID effects.

Diode Failure

Diodes in solar panels are essential components that prevent reverse current flow. Short-circuited bypass diodes result in power loss of 33% or greater and can create hotspots.

To spot diode failure, regularly monitor the system's performance and look for any significant drops in energy production or unusual patterns in the monitoring data. Additionally, inspect the panels for any visible signs of damage or discoloration.

Diode failure can be addressed by replacing the faulty diodes. Early detection and prompt replacement can help prevent further damage and ensure the optimal performance of the solar installation.

Solar Panels Are Resilient, But Not Infallible

It’s critical for solar energy systems to perform as expected to have profitable projects. If PV systems aren’t producing the anticipated solar electricity output, it’s essential for solar contractors to identify and mitigate issues. Depending on the defect and cause, they may be covered by module warranties. Understanding the issues will help you pinpoint problems and educate clients on how to resolve them.

Want to stay current on solar energy industry trends? Check out the GreenLancer blog!

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