Solar Panel Degradation: Understanding Long-Term Performance in 2026
What causes solar panel degradation, how much is normal, and how to ensure your modules meet the 25-year warranty curve.
What Is Solar Panel Degradation?
All solar panels lose a small amount of output power every year due to material aging, UV exposure, thermal cycling, and cell-level physics. This is called degradation. Modern modules are warrantied to lose less than 0.4%/year linearly, meaning after 25 years a panel should still produce at least 87.4% of its nameplate power. Understanding degradation is critical for accurate long-term energy yield forecasts and LCOE calculations.
Types of Degradation
(1) Light Induced Degradation (LID): First-exposure power loss, typically <1% for good N-type modules, up to 3% for old P-type. (2) Potential Induced Degradation (PID): Caused by voltage stress in humid environments, can be 5-20% if unmitigated. Modern anti-PID designs prevent this. (3) Thermal cycling: Gradual degradation from temperature swings. (4) UV degradation: Breakdown of EVA encapsulant. (5) Micro-cracks: From shipping, installation, or hail damage, can cause step changes in output.
N-Type vs P-Type Degradation
N-type cells (TOPCon, HJT) have inherently lower degradation than P-type (PERC): N-type has no Boron-Oxygen defect complex that causes LID in P-type. N-type shows near-zero LID vs 1-3% for P-type. Annual degradation: 0.4%/yr for TOPCon, 0.35%/yr for HJT, vs 0.55%/yr for PERC. Over 25 years, this difference compounds: JUSTSOLAR HJT retains 88.8% at year 25 vs 85-87% for typical PERC modules.
Warranty Curves
Good manufacturers offer a linear performance warranty: Year 1: <1% degradation, meaning modules produce ≥99%. Annual thereafter: ≤0.4% loss per year. Year 25: ≥87.4% output guaranteed. Year 30: ≥84.8% (JUSTSOLAR extended). If actual output falls below this curve, manufacturer compensates the difference (replacement modules, credit, or payment). Read the fine print: what's measured, how, at what conditions.
Real-World vs Warranty Curves
Independent field studies (NREL, Fraunhofer, DNV) show real-world degradation typically beats warranty curves: Median annual degradation 0.5-0.8%/yr for older PERC/multi modules, 0.3-0.5%/yr for new N-type. Better performing sites: utility-scale in moderate climates. Worse performing sites: hot humid climates, coastal (salt), poor installation. Good O&M (cleaning, monitoring) helps modules match or exceed warranty expectations.
JUSTSOLAR Degradation Performance
All JUSTSOLAR modules meet or exceed industry warranty curves: TOPCon series: <1% Year 1, 0.4%/yr annual, ≥87.4% at Year 25. HJT series: <1% Year 1, 0.35%/yr annual, ≥88.8% at Year 25, ≥84.8% at Year 30. We provide TUV-certified degradation test data on request. Real field installations from 2011-onwards show our TOPCon modules performing at or above warranty curves — data available for site references.
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