Solar Efficiency Losses Over Time

How much do solar panels decrease over time? The solar industry standard is a conservative estimate of 3% in the first year, and less than 1% per year after that. However, solar panel manufacturers are starting to realize that this is too conservative, and they are beginning to warranty their panels to more realistic degradation rates.

There are three points I want to make.

  1. Use the solar panel’s warranty to compare output loss over time because that is the only output you are guaranteed.
  2. Realistically expect less than a 3% decrease in output the first year, and about .5% decrease per year after that for most panels.
  3. One solar panel from 1979 was tested in 2010 (after 30 years) and its output was better than the original factory specs.