Solar Panel Fault Diagnosis Example on a Brisbane Roof

A homeowner notices the same pattern for three weeks: the solar system is producing well below its usual daytime output, despite clear Brisbane weather and no alert on the inverter. This solar panel fault diagnosis example shows why low production should not be blamed on dirty panels alone – and why a structured inspection can save time, protect the system and give you clear evidence of what needs attention.

The system in this example is a typical residential installation: two panel strings on a tiled roof, an inverter in the garage and a monitoring app that records daily generation. It had performed reliably for several years. Then output dropped by around 25 to 30 per cent compared with similar sunny periods from the previous year.

That number is a useful starting point, but it is not a diagnosis. Solar output changes with season, cloud cover, heat, shading and household monitoring settings. The job is to separate normal variation from a genuine performance issue.

Solar Panel Fault Diagnosis Example: Starting With the Evidence

A proper diagnosis begins before anyone steps onto the roof. The first check is the available production history. Looking at daily and monthly figures helps establish whether the fall was sudden, gradual or limited to certain times of day.

A sudden fall can point to an inverter shutdown, connection issue or isolated equipment fault. A gradual reduction may be associated with soiling, new shading, bird activity or an accumulating roof issue. If the graph drops at the same time each afternoon, shade from tree growth or a new nearby structure may be more likely than a panel fault.

In this case, the monitoring data showed a gradual decline rather than an overnight change. The inverter screen did not display a fault code, and generation still rose in the morning as expected. That ruled out nothing, but it suggested the system was operating rather than completely offline.

The inspection then compared the inverter’s live readings with expected conditions on site. A reading taken in isolation can mislead. Panel temperature, cloud movement and the time of day all affect output. The useful comparison is between strings, where available, and between the system’s current behaviour and its established production pattern.

What the Roof Inspection Found

Once roof access is safe, the visual inspection looks beyond the glass surface. Panels, frames, clamps, cabling, isolators, roof penetrations and the area beneath the array all matter. Pigeons frequently create problems that are not visible from the ground, particularly where they nest under panels and leave droppings across the lower edge of the array.

On this roof, the inspection found four relevant issues:

• Heavy bird droppings and dust were concentrated on several lower panels.
• Nesting material had collected beneath the array, holding moisture and restricting access for inspection.
• One section of cabling showed signs of abrasion where it had been rubbing against roof material.
• A single panel appeared noticeably hotter than adjacent panels during thermal imaging.

The first finding could explain some lost production. Even partial soiling can affect a panel string because panels operate together. The impact depends on the panel layout, the location of the dirt and whether bypass diodes are activated. A light film of dust may have little effect, while dense droppings across critical cells can have a much greater impact.

The second finding mattered because bird nests are not just a cleaning problem. They can encourage ongoing debris build-up, create persistent soiling and make it harder to see developing cable or roof issues. Bird proofing is most effective after the area has been cleaned and checked, not as a quick cover-up over nesting material.

The cable abrasion was a more serious concern. It did not confirm an electrical fault by itself, but any damaged or poorly supported cable needs assessment by an appropriately licensed solar electrician. Roof movement, heat and ongoing rubbing can turn a minor defect into a safety or performance issue.

Why Thermal Imaging Changed the Picture

Thermal imaging is valuable because it can reveal temperature differences that cannot be seen with the naked eye. A panel or cell running hotter than surrounding areas may indicate a developing issue such as a damaged cell, a faulty bypass diode, poor connection or localised electrical resistance.

In this example, the thermal image showed one panel with a distinct hot area compared with matching panels beside it. The panel surface was clean enough after the initial assessment for the temperature difference to remain meaningful. If the hot area had simply lined up with a heavy patch of droppings, the explanation may have been external shading and soiling instead.

This is where good diagnosis requires restraint. A thermal image identifies an abnormal pattern, not always the exact component that has failed. It provides strong evidence for the next step, which may include electrical testing and warranty assessment by a licensed solar electrician.

The homeowner’s report should record the image, its location in the array, the conditions at the time and clear photographs of the panel layout. That documentation is far more useful than being told that a panel “looks a bit hot”. It gives the owner a practical record to use when arranging further electrical assessment or discussing a possible warranty claim.

Cleaning, Protection and Faults Are Different Jobs

One reason solar problems are missed is that people expect a clean to fix every performance issue. Professional solar panel cleaning can remove grime, bird droppings and organic debris that reduce light reaching the cells. It also creates an opportunity to inspect the array closely and collect before-and-after performance observations.

However, cleaning cannot repair damaged cells, degraded internal components, loose electrical connections or inverter faults. Similarly, a thermal scan can identify a concern but does not replace the electrical work needed to confirm and rectify it.

In this case, cleaning the array and removing nesting debris addressed a clear source of performance loss. Bird proofing was then recommended to stop pigeons returning beneath the panels. The abnormal thermal result and cable wear were documented separately as electrical follow-up items, rather than being presented as issues solved by cleaning.

That distinction matters for your budget and your safety. It prevents unnecessary electrical work where soiling is the main issue, while ensuring a genuine fault is not dismissed as dirt on the panels.

How the Diagnosis Becomes an Action Plan

A useful solar maintenance report should leave the property owner with decisions, not jargon. For this example, the action plan was straightforward: clean the affected panels, remove nesting material, install suitable bird proofing to prevent repeat contamination and arrange licensed electrical assessment of the abraded cable and hot panel.

The order can vary. If an inspection reveals an immediate electrical safety concern, electrical isolation and assessment take priority over cleaning. If no urgent hazard is identified, cleaning and bird removal may be completed first so the system can be reassessed under clearer operating conditions.

After the panels were cleaned, output should be monitored across comparable sunny days rather than judged from one afternoon. A noticeable improvement would support the finding that soiling was contributing to the loss. If output remains below the expected range, the documented thermal anomaly becomes even more significant.

For commercial systems, this process is particularly valuable because a small percentage loss across a large array can become a substantial annual cost. Facilities managers benefit from dated photographs, thermal images, observations by array section and a record of recommended actions. It makes maintenance planning easier and provides a defensible trail when multiple contractors or stakeholders are involved.

When to Arrange a Check

A production graph that is consistently below its normal seasonal pattern deserves attention, especially if the system has previously performed well. Other signs include recurring bird activity, visible droppings, debris under panels, inverter warnings, a sudden production drop or a system that appears to be generating less than a comparable neighbouring system.

Do not climb onto the roof to investigate cabling, panels or isolators yourself. Solar work combines roof-access risk with electrical equipment, and the problem is not always visible from ground level. A professional inspection can assess the physical condition of the array, identify soiling and nesting issues, use thermal imaging where appropriate and document any concerns requiring electrical follow-up.

The best result is not simply cleaner panels. It is knowing what affected output, what has been corrected, what still needs attention and what will help protect your solar investment before a small issue becomes an expensive one.