What Is Solar Panel Degradation?
Solar panels degrade gradually over time as the semiconductor materials in the cells are exposed to UV radiation, thermal cycling, and moisture. The industry metric is the degradation rate expressed as percentage of original output lost per year. Modern Tier 1 monocrystalline panels (JA Solar, Trina, LONGi, REC) degrade at 0.3–0.5% per year after the first year.
This means a panel generating 400 Wp when new will produce approximately 395 Wp after one year (0.5% first-year degradation is common), then lose roughly 1.5–2 Wp per year thereafter. After 25 years, the panel is still generating approximately 87–90% of its original rated output — which is why manufacturers are comfortable offering 25-year "linear performance warranties" guaranteeing at least 80% output.
Real-World Data: How Long Do Solar Panels Last?
The oldest commercially-installed solar panels are now over 40 years old and many are still generating electricity. Lawrence Berkeley National Laboratory (LBNL) analysed over 54,000 solar projects and found median degradation rates of 0.5%/year — consistent with manufacturer warranties. The NREL (National Renewable Energy Laboratory) studied systems from 1980–2012 and found a median degradation rate of 0.45%/year, with only 0.4% of analysed systems showing catastrophic failure.
In practice, panels rarely fail suddenly. The most common end-of-life failure mode is delamination (moisture ingress causing the encapsulant to separate) which typically takes 25–35 years to develop. Inverters, by contrast, are the component most likely to need replacement — typically at 10–15 years.
25-Year Warranties: What They Actually Cover
Most Tier 1 panel manufacturers offer two warranties: a product warranty (covering manufacturing defects, typically 12–15 years) and a linear performance warranty (covering output degradation, typically 25 years). The performance warranty guarantees that output will not fall below a certain percentage of rated output — usually 80% at 25 years and 92% at 10 years.
Claiming on a 25-year warranty is rarely necessary because degradation is gradual and rarely breaches warranty thresholds. The practical purpose of the warranty is that it tells you the manufacturer has tested degradation rates and is confident the panels will last. A manufacturer offering 25-year performance warranties has strong incentive to use quality encapsulants, glass, and EVA film — because warranty claims are expensive.
When to Replace Solar Panels
For a system installed in East Anglia in 2026, the replacement decision will likely not arise until 2050–2060. By that point, solar panel efficiency will have increased significantly — replacement panels will likely be 25–30% efficient versus today's 21–22%. The economics of replacement will depend on the cost of new panels (likely to be very low by then) versus the value of the additional generation from higher-efficiency replacements.
If you have a very old system (pre-2010) that is still operating but showing significant degradation, a panel-by-panel power output test can identify weak panels for targeted replacement. We offer solar health checks and performance audits for older East Anglia systems.
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