Like everything else, PV modules degrade with time. The aging or derating factor is usually covered by the manufacturer performance warranty. Most major brands, listed in the table below guarantee a maximum of 20% de-rating over 25 years, with different milestones during that period. Some manufacturers include the initial LID at year 1 with values varying from 2.5% to 3.5%.


Major Manufacturers Derating Warranty

In reality, the PV de-rating would be lower than the guaranteed limit. Solar system design can use 15%.


Other performance factors

  1. GHI to POA ratio
  2. Far shading
  3. Inter-shading
  4. IAM
  5. Soiling
  6. Snow
  7. Low irradiance
  8. Temperature
  9. Module quality
  10. Mismatch
  11. Inverter efficiency
  12. Power clipping
  13. Wiring
  14. Transformer
  15. Dispatch
  16. PID
  17. Light soaking
  18. Aging