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Data Acquisition

Troubleshooting Lesser-Known Solar Module Anomalies

By November 10, 2023April 1st, 2024No Comments

Although solar energy appears to be a simple concept, several lesser-known anomalies exist beneath the surface. Everyone is familiar with common issues like open circuit string anomalies and hotspots, but this blog will discuss 2 often unrecognized anomalies that also impact solar module efficiency and longevity.

Let’s shed light on the lesser-known anomalies that can be equally destructive, if not more.


1. Single Diode and Multi Diode Issues

Diodes play a crucial role in solar module installations. They are used as blocking devices to prevent current backflow, ensuring that the current flows in only one direction. Additionally, they act as bypass devices that help to maintain the reliability of the entire solar power system in the event of a solar module substring failure.

What causes it?

The diode, meant to bypass the substring, has been damaged and now allows current to flow through it at all times.

This damage is typically caused by an extremely high current passing through the PV module due to lightning, which can permanently malfunction the diode.

What are the symptoms?

When several cells in a PV module are at a high temperature, they are known as Multi-hot Spots. However, if these cells are located in the same substring, the root cause will likely be the diode. In such cases, one-third of the PV module typically shows a high-temperature variation in the cells, while the rest has a consistent temperature. This issue is known as a single-diode problem.

Example of a Single Diode Anomaly

Like a single-diode issue, the multi-diode issue has more than one substring affected. The difference compared to a multi-hotspot issue is that the anomalies follow the line of the substrings and appear linear.

Example of a Multi-diode Anomaly
Example of a multi-diode anomaly in thermal view

It is common for people to mistake this defect with a single or double bypassed substring. The affected cells have the same temperature in this particular situation, and the whole substring shows homogeneously hotter than other substrings in the same module. This thermal pattern shows that the bypass diode works properly. In the case of a single or multi-diode issue, all cells become hotter, and the thermographic images will display an irregular checkerboard pattern on the affected substring instead of a homogenous temperature increase.

Example of a single bypassed substring in the thermal image.

How can you fix it?

You will have to change the whole PV module if replacing the diode is not an option.

2. String Issues – Reversed Polarity

Last, you have reversed polarity, which occurs on the string level.

What causes it?

Reversed polarity can cause the photovoltaic cells to generate electricity in the opposite direction, reducing energy production, system inefficiency, and possible damage to the solar equipment. Hence, it is crucial to ensure correct polarity during installation to optimize the performance of solar panels.

What are the symptoms?

One group of contiguous panels shows a patchwork pattern (panels with multi-hotspots), usually the whole string.

Reversed Polarity Example
Reversed Polarity in thermal

How can you fix it?

Start by thoroughly checking string connections. Address these issues promptly, as they cause extreme power losses and are often easy to fix.

It is essential to correctly wire solar panels’ positive and negative electrical connections to prevent reversed polarity.


Understanding and addressing these lesser-known anomalies can make a substantial difference in the performance and longevity of your solar power system. Therefore, it is vital to perform regular thermal inspections on your solar sites to avoid anomalies becoming a major issue and causing severe output loss.

By creating a digital twin of your site, you can keep track of your site’s health and mitigate issues quickly.

Get in touch to learn how to digitalize your solar site!