Chapter 7

Introduction

No solar power system remains exactly the same throughout its lifetime. From the day it is first commissioned, every component is exposed to changing temperatures, sunlight, wind, rain and countless heating and cooling cycles.

These environmental conditions gradually affect the materials from which the system is built. Most of these changes occur slowly. A solar panel that is twenty years old will usually look almost identical to one installed yesterday, yet careful measurements reveal that it produces slightly less electricity than it once did. This gradual ageing is entirely normal.

Occasionally, however, a reduction in performance is caused not by ageing but by a fault. A damaged panel, failed inverter or loose electrical connection can reduce generation far more rapidly than natural degradation alone. Understanding the difference between normal ageing and genuine equipment failure is essential for maintaining a reliable solar power system.

Normal Performance Degradation

Solar panels do not suddenly stop working when they reach the end of their warranty. Instead, their power output slowly decreases over many years.

Most modern panels lose only a small fraction of their performance each year, typically around 0.3–0.5% annually after their initial stabilisation period. This means a panel producing 100% of its rated power when new may still produce around 87–92% after twenty-five years. This gradual reduction is expected by manufacturers and is reflected in their performance warranties. Rather than indicating a fault, it simply represents the normal ageing of the photovoltaic materials.

Why Solar Panels Performance Decreases Over Time

Several natural processes contribute to this gradual reduction in performance. During the first few weeks of operation, many silicon panels experience a small initial reduction in output known as light-induced degradation (LID) as the cells stabilise under sunlight.

Over much longer periods, prolonged electrical stress can lead to potential-induced degradation (PID) in certain conditions, causing additional power losses if not properly controlled. The panels themselves are also continually exposed to ultraviolet radiation, moisture, wind, temperature changes and mechanical stress. Every sunrise warms the modules. Every sunset cools them again.

Over decades, these repeated expansion and contraction cycles slowly age the materials that protect the solar cells.

Manufacturers carefully design modern panels to minimise these effects, allowing most systems to continue operating reliably for many decades.

When Ageing Becomes Damage

Although gradual ageing is expected, physical damage is not. Severe weather, accidental impacts or manufacturing defects can damage the protective glass, encapsulant or solar cells themselves.

Small cell cracks may initially have little effect on performance, but repeated thermal cycling can allow them to grow over time.

In some cases, the protective layers begin separating, a process known as delamination, allowing moisture to enter the module and accelerate further deterioration.

Fortunately, modern solar panels are extremely durable, and significant damage remains relatively uncommon. Routine inspections help identify these problems long before they become serious.

Common System Faults

Not every reduction in energy production originates within the solar panels. Other components throughout the installation may also develop faults during their operating life. Electrical connections can gradually loosen due to thermal expansion and contraction. Connectors may become damaged. Circuit breakers or isolators may trip because of genuine electrical faults.

Electronic components inside the inverter may eventually reach the end of their service life, while optimisers or microinverters can occasionally fail on individual panels.

External conditions can also change. Trees continue growing, new buildings may introduce additional shading and accumulated dirt may reduce generation if left unaddressed. Many apparent "panel faults" are ultimately traced to one of these external factors rather than the panels themselves.

Diagnosing Reduced Performance

When monitoring indicates that electricity generation has fallen below expectations, engineers follow a structured fault-finding process. 

The first question is whether the reduction matches normal seasonal variation or the gradual degradation expected for the system's age. If the decrease is unusually large or occurs suddenly, further investigation begins. Monitoring data, inspection records and electrical measurements are combined to narrow down the possible causes. The inverter is checked for fault messages. Visual inspections look for damaged panels, loose connections or new shading. Electrical tests confirm whether individual strings are performing as expected.

Rather than replacing components immediately, engineers work systematically to identify the true cause before corrective action is taken. This logical approach reduces unnecessary repairs while ensuring genuine faults are resolved efficiently.

Repair, Replacement and Warranties

Once the cause has been identified, the appropriate solution can be selected. Minor issues such as loose cable connections, vegetation growth or dirty panels can often be corrected quickly.

Other faults may require damaged panels, optimisers or inverters to be repaired or replaced. Manufacturer warranties help protect owners against premature equipment failures. Most solar panels include both a product warranty, covering defects in materials and workmanship, and a performance warranty, guaranteeing that the panels retain a specified percentage of their original output over time.

These warranties recognise an important distinction. Gradual performance degradation is expected. Premature equipment failure is not. Understanding this difference helps determine whether reduced performance represents normal ageing or a fault that should be investigated under warranty.

Looking Ahead

A well-designed solar power system can continue producing clean electricity for decades. Its performance gradually changes.

Occasionally, components are repaired or replaced. Technology improves. The system evolves throughout its lifetime.

In the final chapter of Part 6, we'll follow a solar installation from the day it is commissioned through decades of operation, exploring how maintenance, repairs, equipment upgrades and eventual replacement combine to tell the complete life story of a solar power system.