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.
Verify the Offered Warranty Curve
Degradation limits and warranty periods vary by model and market. Compare the offered datasheet, warranty document and applicable certificates for the exact SKU, then record the agreed documents and remedy path in the contract package.
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