Solar energy systems are designed to deliver reliable performance for many years, yet every system will slowly produce less electricity. For homeowners and businesses that rely on stable power bills, this decline can be frustrating and confusing. Platinum Solar Group explains why solar systems lose performance, how to recognise when something is wrong and what can be done to restore lost output. By understanding the difference between normal ageing and avoidable faults, readers can make better decisions about maintenance, solar system repairs and long-term returns on their investment.
The discussion covers natural panel degradation, environmental impacts and the role of monitoring in spotting problems early. Solar installers will also outline the warning signs that suggest a system needs professional attention. With clear insight, readers will learn when simple cleaning is enough, when component replacement is justified and when a full system review is the smartest path to protecting performance and savings.
Over time, every solar system will produce slightly less energy than when it was brand new. This is called normal degradation, and it is already factored into product warranties and performance expectations. True performance loss is different. It is when the system is underperforming compared with what it should be delivering for its age, conditions and design.
Understanding the difference helps homeowners know when to simply expect lower output on an older system and when to call solar experts to investigate a potential fault or damage.
All quality panels lose a small percentage of output each year as materials naturally age in the sun. Most modern panels degrade at around 0.3 to 0.7% per year after the first year, and manufacturers usually guarantee that the panels will still produce around 80 to 85% of their original output after 25 years.
On a typical 6.6 kW system, this means:
This drop is smooth and predictable. There are no sudden cliffs in performance, and both strings of panels should decline at a similar rate. When solar analysts review monitoring data for a normally degrading system, the daily and monthly production curves still follow the sun and seasons as expected, just at a slightly lower level each year.
True performance loss shows up as unexpected or uneven drops that go beyond the normal degradation rate or that appear suddenly. Be mindful of these warnings:
Common causes of real performance loss include failed or cracked panels, water ingress, hot spot bypass, diode failures, loose or corroded DC connections, inverter faults and new shading from trees or nearby structures. None of these are part of normal ageing, and they usually justify inspection and testing.
To tell the difference between normal degradation and a problem, the system’s actual performance needs to be compared with what is expected. Solar installers look at:
If a 10‑year‑old system is consistently producing around 90 to 95% of its original estimated output in similar conditions, this aligns with normal degradation. If it is closer to 70% or if one part of the system is lagging far behind the rest, this indicates true performance loss and the need for a detailed fault diagnosis and potential repairs.
Some solar performance problems only show up years after installation. The system might have been installed correctly for day‑one conditions, yet still lose efficiency faster than expected because of design choices that did not fully account for shade, roof layout, heat or future electricity use. These are not always “faults” but limitations that become obvious only once the system has lived through a few summers and winters.
Understanding these hidden design constraints helps homeowners decide whether simple tweaks, component upgrades or more substantial design changes are needed to recover performance. Solar analysts focus on identifying whether an issue is a design limitation or a genuine fault, so clients only spend money where it makes a real difference.
Panel strings are typically designed to complement existing shade at the time of installation. Over several years, trees grow taller, neighbouring buildings rise and new aerials appear. A string layout that worked originally can become a bottleneck because one shaded panel drags down the current of every panel in that string.
This problem is most obvious when generation seems decent in the middle of the day but drops sharply in the early morning or late afternoon compared with earlier years. A performance check reveals that shade patterns have changed even if the homeowner has not noticed them.
Depending on the inverter and panel configuration, the solution may be to:
Not every roof allows a perfect layout, but a thoughtful redesign can often recover a surprising amount of lost output.
Installations are usually sized for the household’s needs at the time. Many homes add air conditioning, EV chargers, pools or electric hot water. What was once a well‑matched system can become undersized, so the family starts importing a lot more power from the grid and the solar system appears to be “underperforming”.
Sometimes the original inverter is also slightly undersized to save on upfront costs or to comply with network limits. A moderate oversizing of panels is normal, but if extra loads are added later, the inverter can spend long periods operating at its maximum output and clipping production.
In these cases, solar installers assess:
The fix might be as simple as adding more panels within the existing inverter limit or as involved as upgrading the inverter to match new household demand.
Designs that look fine on paper can struggle in real‑world heat. Inverters mounted in full sun or tight cupboards run hotter, which triggers internal protection and reduces output during the hottest parts of the day. Similarly, long cable runs or undersized cables increase resistance, which permanently shaves a small but measurable percentage off production.
These limitations often only become clear during monitoring over a couple of summers. If we see regular output dips in the heat of the day or unusual voltage drops, technicians may recommend relocating the inverter to a shaded, ventilated spot, improving airflow or upgrading key cable runs to reduce losses and stabilise performance.
As solar systems age, the inverter is often the first major component to lose efficiency and reliability. While panels commonly last 20 to 30 years, many have a practical life of 10 to 15 years before performance noticeably declines. For many underperforming systems, the inverter has become the bottleneck that limits how much solar energy can actually be delivered to the home or business.
Solar analysts find that restoring output is less about the panels and more about addressing an ageing or incorrectly specified inverter. Understanding how inverter ageing works helps owners decide when a simple setting adjustment is enough and when a repair or full replacement is the smarter choice.
Inverters work hard every sunny day, converting high-voltage DC power from the panels into AC power for the property. Heat cycling, component wear and electrical stress reduce efficiency. Loss in conversion efficiency adds up to hundreds of kilowatt hours per year for a typical residential system.
Effects include reduced maximum power output, increased internal resistance and less accurate tracking of the panel's maximum power point. This means the inverter might start clipping more often on bright days or fail to respond quickly to passing clouds, reducing the total energy harvested. Owners may also notice that the system hits its peak output earlier in the day, then levels off instead of sustaining high production.
Most quality inverters are rated to lose a small amount of efficiency, but harsh conditions can accelerate this process. Units installed in hot, unshaded areas or in dusty coastal environments often show earlier performance decline than inverters in cool, well-ventilated locations.
Ageing inverters rarely fail overnight. Instead, there is usually a period of subtle underperformance followed by more obvious warning signs. Typical symptoms include:
Another sign is mismatched performance between strings or MPPT trackers, where one input underperforms despite panels and cabling testing correctly. In these cases, the internal electronics that manage power tracking are often degrading.
Whether an ageing inverter should be repaired or replaced depends on its age, warranty, status, fault type and system goals. For new inverters still under manufacturer warranty, repair or warranty replacement is usually the first step. This can involve firmware updates, fan replacement or board swaps that restore full function.
For inverters older than 8 to 10 years, replacement is often more economical. Newer models are typically more efficient, have better monitoring, include updated safety features and can be better matched to any panel upgrades. In some cases, solar installers will recommend upsizing the inverter slightly if the original unit was undersized for local conditions or if future battery storage is planned.
Timely action is important. Running an inverter that is clearly struggling can lead to more sudden failure at an inconvenient time and can quietly waste significant solar production year after year. Regular performance checks and monitoring alerts help catch inverter ageing early so repairs or upgrades can be planned rather than rushed.
The electrical side of a solar system can quietly reduce output long before anything stops working completely. Performance may drop each year due to small faults in cabling, connections or protection devices that only show up on careful testing. These are issues most owners cannot see on the roof or at the inverter, but they have a real impact on power production and safety.
Solar analysts focus on identifying these slow-developing electrical problems during inspections so the system keeps working close to its original design. Knowing the common issues helps owners understand when a quick repair or adjustment is needed instead of assuming panels have simply worn out.
Every solar system has dozens of electrical joints in roof isolators, junction boxes, DC plugs and AC switchboards. With heat, UV exposure and normal expansion and contraction, screws can loosen and plug-style connectors can move slightly apart. This creates higher resistance, which turns solar energy into unwanted heat instead of power.
In coastal or humid areas, corrosion is a major factor. Moisture can get into cracked seals or poorly installed connectors and slowly oxidise metal surfaces. The result is:
Solar technicians check torque on terminals, inspect for heat discolouration and replace any discoloured or non-compliant connectors. Using the correct matching DC plugs and weatherproof glands is critical whenever repairs are made, so the same issue does not return.
DC and AC cables are designed to last, but long-term UV exposure, physical abrasion under roof sheets or rodent damage can break down the outer sheath. Even small cracks let in moisture, affecting insulation resistance between conductors or to earth.
Early signs are not always visible. Instead, performance might drop slightly on damp mornings, then recover in dry weather. In more advanced stages, safety devices may start tripping under certain conditions. During maintenance, solar technicians will test insulation resistance with specialised metres to pick up issues before they become dangerous.
If a damaged cable is found, the practical fix is to cut back to clean insulation and install new runs with proper mechanical protection, such as conduit or saddles. Simply taping over degraded insulation is not considered an acceptable repair.
DC isolators on the roof and besides the inverter are exposed to heat and weather every day. Internal contacts can pit or carbonise each time they operate, which increases resistance and reduces system efficiency. In some cases, plastic housings also become brittle and allow water to enter.
Fuses and circuit breakers can also deteriorate, particularly if they have been running close to their rated current. Contacts inside the inverter terminals can loosen or suffer from heat cycling, which again wastes energy as heat.
During a service, solar analysts will operate and test isolators, check for water ingress, inspect breakers for heat marks and retighten inverter terminations to manufacturer specifications. Where components show signs of ageing or water damage, proactive replacement is recommended to restore performance and protect the system for the long term.
Solar owners often assume that if their monitoring app looks “normal”, the system must be healthy. In reality, a system can lose a significant amount of performance while the graphs still appear acceptable at a glance. Relying on monitoring alone can delay repairs and leave lost savings unnoticed for years.
Platinum Solar Group sees many issues only discovered during inspections or bill reviews, even though the monitoring portal showed no obvious alarm. Understanding the blind spots in monitoring helps owners know when to investigate further.
Most monitoring portals show relative shapes rather than absolute performance. On a sunny day, the curve still rises in the morning, peaks at midday and falls in the afternoon, even if overall output has dropped 10 to 3%.
Gradual problems, such as panel soiling, thermal degradation or minor shading, usually reduce all strings by a similar proportion. The daily curve looks “right”, so the owner does not suspect a problem. Without comparing current production to:
It is easy to miss a slow decline that adds up to large financial losses.
Monitoring systems are usually designed to flag complete failures, such as a dead inverter or offline communication. Partial issues often do not trigger an alert.
Examples include a single underperforming panel in a string, a weak MPPT channel in the inverter or a faulty DC connector causing only a small voltage drop. The overall system may still operate at 80 to 90%, so the portal shows power flowing and no error code. From the customer’s view, everything “works” even though performance is clearly below what a healthy array should deliver.
Many casually compare “today vs last week” in their app. Weather, temperature and seasonal changes make these comparisons unreliable.
Cloud cover, heat haze, bushfire smoke and higher summer panel temperatures all reduce output without any fault in the system. At the same time, a genuine fault that develops during a run of poor weather can be masked because the owner expects numbers to be a bit lower anyway.
Proper performance assessment needs weather-adjusted analysis across longer periods, along with checks against electricity bills and estimated yield. Solar technicians often cross-check monitoring data with grid consumption and export figures to confirm whether the system is truly delivering what it should.
Not all drops in solar output are “just how solar works”. Sometimes a system is performing exactly in line with its design limits and local conditions. Other times, a fault or installation issue is holding it back, and repairs will recover lost production. Knowing the difference helps owners avoid unnecessary worry or missed warranty claims.
Solar technicians look at the original system design and live performance data to decide whether a system needs repair or simply has realistic limits based on roof size, orientation and local climate.
The first step is to compare actual generation with what a correctly working system of the same size and layout should produce. That means looking at:
If a 6.6 kW system was modelled to average 24 kWh per day over a year but is only delivering 12 to 15 kWh in similar weather conditions, and the site is not heavily shaded, this usually indicates a repair issue.
Underperformance becomes a repair issue when there is a clear technical cause that can be corrected. Common examples are:
These problems usually show up as sudden or step changes in output rather than the slow 0.5 to 0.8% per year degradation expected from quality panels. Monitoring data may show one string producing far less than another or sharp drops in the middle of sunny days.
Sometimes what looks like underperformance is actually the system operating within its design constraints. Examples include:
In these situations, the system may be healthy, and no repair will increase production. Improving performance would require design changes rather than fixing a fault.
The most important lesson is that solar is not a “set and forget” asset; it’s a high‑value piece of infrastructure that behaves like any other business investment. Panel degradation, dirt and shading, ageing inverters, wiring and connection issues, weather damage and even software or monitoring faults all chip away at performance bit by bit. Left unchecked, those small losses become real money off the bottom line through higher grid consumption and lower returns on the original capital outlay. The flip side is that most performance issues are completely manageable, provided there is a structured maintenance plan, live system monitoring, clear performance benchmarks and a relationship with a qualified solar service team that knows when a simple clean or firmware update will do. By treating the solar system as a long‑term strategic asset, it’s possible to lock in predictable energy savings, protect cash flow from rising power prices and keep the entire system operating safely.
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