Module degradation is the power an individual module loses over time. System degradation is the energy the whole PV plant loses over time, and the two are not always equal. Modules in the field age at different rates. The weaker ones limit the current of the strings or substrings around them, so the extra mismatch makes the system lose more than the average module does. In practice the plant can show a larger drop in energy even while the average module is still within its warranty. To confirm it, compare long-term normalized plant output and string or inverter trends with IV curve data and module test results. This separates average module degradation from degradation caused by mismatch. Model degradation at the system level and include the spread between modules, not only the module warranty rate.
caused_byc1 verified · fact Module degradation
Individual modules lose power over time; system loss follows from this but is not always the same number.
sec=h4 h=3675d15ba302verified by: joshuahamsaverified on: 2026-10-16review note: support check: partial - Passage says system and module degradation differ and mismatch arises from uneven aging, but doesn't state system degradation is caused by module degradation in general.
c2 verified · fact Uneven module aging
Modules aging at different rates creates electrical mismatch, because weaker modules limit current in the strings or substrings around them.
sec=h2 h=14c4627b4866sec=h5 h=994460afbabcsec=h4 h=3675d15ba302sec=h6 h=03fbe99d08d3verified by: joshuahamsaverified on: 2026-10-16
presents_asc3 verified · fact Gradual performance decline
The system energy decline can be larger than the average module loss, even while the average module is still within warranty.
sec=h5 h=994460afbabcverified by: joshuahamsaverified on: 2026-10-16
detected_byc4 verified · fact Normalized output trend analysis
Long-term normalized plant output helps separate average module degradation from degradation driven by mismatch.
sec=h2 h=14c4627b4866sec=front h=ff0c8c5f07ccverified by: joshuahamsaverified on: 2026-10-16
c5 verified · fact String and inverter trending
sec=h2 h=14c4627b4866sec=front h=ff0c8c5f07ccverified by: joshuahamsaverified on: 2026-10-16
c6 drafted · lead IV curve tracing
sec=h2 h=14c4627b4866sec=front h=ff0c8c5f07ccsec=h6 h=03fbe99d08d3c7 drafted · lead Flash testing
The source refers generally to module test results used to establish average module degradation.
sec=h2 h=14c4627b4866sec=front h=ff0c8c5f07ccreview note: support check: partial - Passages mention generic 'module test results', not flash testing specifically, though the note acknowledges this generality.
mitigated_byc8 drafted · lead System-level degradation modeling
The performance model should include system-level degradation, not just module-level degradation.
sec=h2 h=14c4627b4866sec=front h=ff0c8c5f07ccsec=h6 h=03fbe99d08d3c9 drafted · lead Production forecast update
Use field measurements, module technology, warranty terms and IV or string data to update long-term energy assumptions.
sec=h2 h=14c4627b4866sec=front h=ff0c8c5f07ccsec=h6 h=03fbe99d08d3degradation_ratec10 verified · fact nominal 0.1 PERCENT-PER-YR
Conditions: Modeling allowance that some independent engineers add on top of the module degradation rate to account for mismatch from uneven module aging; not a universal rule.
Some independent engineers add about 0.1% per year to the module degradation rate when evaluating system degradation.
sec=h6 h=03fbe99d08d3verified by: joshuahamsaverified on: 2026-10-16
explains c5