Solar panel degradation: how much output you lose per year
Panels slowly lose output — about 0.5% per year for modern modules. After 25 years, expect roughly 88% of original output.
Field studies of thousands of systems find median degradation near 0.5%/yr, with premium modules often warrantied at 0.25–0.4%/yr. Solar Plan Builder applies 0.5%/yr to lifetime economics.
What this means for you: Check the warranty’s year-25 output guarantee when comparing panels.