Identifying and Resolving Photovoltaic Faults: An Overview of the Most Common Problems

A photovoltaic (PV) system is designed to generate electricity reliably for decades. In practice, however, reduced performance, inverter error messages, or yields that fall significantly short of expectations occur time and again. The good news is that most PV faults follow recurring patterns and can be identified quickly with a systematic approach. This article outlines the most common sources of faults, explains how to recognize them, and indicates when it is advisable to contact a qualified specialist.

Why Do Faults Occur in Photovoltaic Systems?

A PV system consists of numerous components that must work together seamlessly: solar modules, cabling, connectors, inverters, and, in modern systems, battery storage units and energy management systems. Any of these components can become a weak point.

In many cases, the root cause lies not in the materials themselves but in the planning or installation process. Cutting corners or failing to work precisely at these stages often leads to reduced energy yields later on.

In general, PV faults can be divided into three categories:

• Planning errors, which occur before installation;
• Installation errors, which arise during system construction, and
• Operational faults, which develop during ongoing operation.

The following sections examine the most important cases in detail.

The Most Common Photovoltaic Faults in Detail

1. Soiling and Shading of the Modules

One of the simplest and, at the same time, most common causes of yield losses is dirt on the modules. Leaves, dust, pollen, bird droppings, or moss growth along the module edges can noticeably reduce energy output.

Shading caused by a growing tree, a newly constructed chimney, or a satellite dish can also significantly impair performance. Even localized shading can be problematic, as it may limit the output of an entire module string.

How to identify and resolve the issue: A visual inspection from the ground is often sufficient. Modules should be cleaned regularly, and sources of shading should be removed whenever possible. In cases of permanent partial shading, retrofitting power optimizers may be a practical solution.

2. Defective or Short-Circuited Bypass Diodes

Bypass diodes protect solar cells from overheating during partial shading by diverting current around the affected area. Following thunderstorms or severe voltage spikes, these diodes can occasionally fail or become short-circuited.

If a bypass diode fails, an entire string may lose its output in the worst-case scenario.

How to identify and resolve the issue: This issue is usually detected through the monitoring system when one string consistently underperforms. Accurate diagnosis—using methods such as thermographic imaging or I-V curve measurements—should be carried out by a qualified specialist.

3. String Failure: One String Stops Producing Power

A classic fault scenario occurs when the monitoring system shows one string suddenly dropping to zero while the remaining strings continue operating normally according to solar irradiation levels. This is a clear indication that the issue is limited to a single string.

Common causes include loose connectors, which may become detached after storms or heavy snow loads, or a fault in an individual module.

How to identify and resolve the issue: When reviewing the monitoring system, do not focus solely on power output in watts. Pay particular attention to the affected string’s direct current voltage (UDC, measured in volts) and direct current (IDC, measured in amperes). These values provide crucial diagnostic information.

An initial visual inspection of connectors is possible; however, repairs involving live electrical components should always be entrusted to a qualified professional.

4. Inverter Faults and Error Codes

The inverter is the heart of the PV system and simultaneously one of its most common sources of faults. It converts the direct current generated by the modules into usable alternating current.

If the inverter displays a red warning light or an error code, further investigation is warranted. Incorrect inverter sizing can also lead to persistent yield losses and extend the system’s payback period.

How to identify and resolve the issue: Record the displayed error code and compare it with the manufacturer’s documentation. Many faults can be resolved by restarting the inverter. If the issue recurs repeatedly, a hardware defect is likely. In practice, this is often remedied by replacing the unit.

5. Errors in Cable Routing and Wiring

Even when no defects are immediately visible, cable routing can conceal numerous potential issues. Excessively large cable bundles reduce current-carrying capacity. Positive and negative conductors should be routed in separate channels.

PV cables must be UV-resistant and installed in a manner that protects them from direct sunlight exposure. On long vertical cable runs, conductors should be secured at regular intervals to prevent damage caused by their own weight.

How to identify and resolve the issue: These faults typically occur during installation and can be difficult to correct afterward. Thorough acceptance testing of the completed system is therefore essential, ideally performed by an independent expert if there is any uncertainty.

6. Planning Errors: Incorrect System Sizing and Outdated Data

Some of the most significant sources of faults arise long before installation begins. When a system is designed using outdated roof drawings, actual dimensions often differ from reality, resulting in a suboptimally sized installation.

Proper coordination between module capacity, inverter specifications, and, where applicable, battery storage systems is equally critical.

How to identify and resolve the issue: Prevention is the only effective solution. A reputable installer should always conduct an on-site assessment rather than relying solely on desk-based planning. Manufacturers provide free design software that competent specialists routinely use.

7. Broken Glass and Mechanical Damage

PV modules are covered with safety glass similar to a car windshield. Cracked front glass, caused by hail, falling branches, or improper installation, is usually visible from the ground and compromises both the module’s performance and its safety.

How to identify and resolve the issue: Carry out a visual inspection, document any affected modules (including for insurance purposes), and arrange for their replacement.

A Systematic Approach to Troubleshooting

Before contacting a specialist, you can often narrow down the issue surprisingly accurately by following a few simple steps:

• Check the monitoring system: Which string or module is affected? Does the problem involve the entire system or only part of it?
• Compare values: Pay attention to voltage (UDC) and current (IDC), not just total power output.
• Review the inverter: Is there an alarm, warning message, or error code?
• Conduct a visual inspection: Are there signs of soiling, shading, glass damage, or loose connectors?
• Document your observations: Record any abnormalities before contacting a service provider.

This preliminary work saves time and makes subsequent diagnosis by professionals considerably more efficient.

When Should You Contact a Specialist?

You can perform an initial assessment yourself. However, whenever live electrical components, measurements on the DC side, or the replacement of system components are involved, specialist expertise is essential for both safety and warranty reasons.

Regular maintenance remains the best protection against costly consequential damage. Having your system inspected at fixed intervals helps identify gradual yield losses before they become expensive problems.

Conclusion

Most photovoltaic faults are not rare occurrences but well-known issues: soiling, shading, defective bypass diodes, string failures, inverter malfunctions, and planning or installation errors.

Anyone familiar with these typical fault patterns, who keeps a close eye on the monitoring system and prioritizes regular maintenance, can help ensure that their PV installation continues to generate electricity reliably throughout its service life.

For accurate diagnosis and repairs, however, it is advisable to rely on an experienced specialist, thereby protecting your investment over the long term.

How can I tell if my photovoltaic system has a fault?

The clearest warning sign is an energy yield that is noticeably lower than expected or below previous years' performance. Review your monitoring data regularly: Is a particular string underperforming, or is the entire system producing less electricity? A red indicator light or error code on the inverter, visible soiling, and cracked module glass are also clear warning signs. Routine visual inspections combined with monitoring checks can identify most issues at an early stage.

Can I fix faults in my PV system myself?

You can safely carry out an initial assessment yourself—for example, by comparing monitoring values, reading inverter error codes, or checking modules for dirt and shading. Cleaning easily accessible modules is also possible. However, whenever live electrical components, measurements on the DC side, or component replacements are involved, a qualified specialist should take over for safety and warranty reasons.

How often should a photovoltaic system be serviced?

As a general rule, professional maintenance should be performed approximately every one to two years, depending on the system's location, size, and environmental conditions. Systems located near trees, busy roads, or agricultural environments tend to accumulate dirt more quickly and may benefit from shorter maintenance intervals. Regular maintenance is the best safeguard against gradual performance losses and costly secondary damage.