Capacity Degradation
Capacity degradation in solar PV refers to the reduction in a module's rated power output over time due to physical and chemical aging mechanisms. Unlike sudden failures, degradation is a gradual process that reduces system output predictably over the 25–30 year system lifespan.
Understanding degradation rates is essential for accurate long-term energy yield forecasts and financial modeling.
Degradation Mechanisms
Light-Induced Degradation (LID): Occurs in the first hours to days of operation in standard p-type silicon cells due to boron-oxygen complex formation. Causes 1–3% first-year power loss. Largely mitigated in modern PERC, TOPCon, and HJT technologies.
Potential-Induced Degradation (PID): Caused by high-voltage leakage currents through the module structure. Preventable with proper system grounding, anti-PID coatings, and module design.
UV Degradation: Long-term UV exposure causes encapsulant yellowing, reducing light transmission to cells.
Thermal Cycling: Daily heating and cooling cycles cause microcracks in cells and solder joints, increasing electrical resistance.
Delamination: Separation of cell laminate layers due to moisture and thermal stress, reducing performance.
Industry Standard Degradation Warranties
Most major panel manufacturers warranty:
- Maximum 2–3% power loss in year 1
- Maximum 0.5–0.7% annual degradation years 2–25
- Minimum 80% rated power at year 25
Higher-quality manufacturers (SunPower, LG, Panasonic, LONGi) offer linear power warranties with 0.4–0.45% annual degradation, representing lower long-term production loss.