DetectionMethod
Normalized output trend analysis
- ID
method:normalized-output-trend- IRI
https://solarlattice.org/kb/method/normalized-output-trend- Status
- active
- Also known as
- normalized production trends, long-term normalized plant output
Normalized output trend analysis follows plant, inverter or string output over a long period after scaling it so that the values can be compared. Output is normalized by dividing it by the module area or the installed power, which lets inverters of different size or loading be compared directly. Used together with string or inverter trends, IV curve data and module test results, it helps separate average module degradation from the extra system degradation caused by mismatch. Comparing units only with each other means the environmental conditions cancel out, so the method is not thrown off by sensor drift or missing sensor data. Normalized trends also show soiling losses: look for output falling during dry periods that availability, clipping, curtailment or irradiance sensor problems do not explain. Small shading effects may not show up in yield or performance ratio trends, so normalized array voltage plotted against module temperature can be a more sensitive check. Before trusting the results, check the data quality, meaning the outliers, missing points and gaps, because these can make some analyses unreliable or impossible.
Claims
produces
c1 drafted · lead
Long-term normalized output decline
Long-term normalized plant output that falls faster than the average module degradation points to mismatch-driven system degradation.
review note: support check: partial - Passages say long-term normalized output is compared to separate mismatch-driven system degradation from module degradation, but don't mention the specific signals (WH, POAI) or irradiance/installed-power normalization details.
c2 verified · fact
Normalized voltage deviation
Array voltage normalized to MPP voltage and plotted against module temperature; samples falling below the usual linear relationship showed partial shading that yield and PR plots did not reveal.
verified by: joshuahamsaverified on: 2026-10-20
c3 verified · fact
Spread in normalized inverter yield
Output is normalized to module area or installed power so that inverters or sub-arrays can be compared. A unit that departs from the others is flagged.
verified by: joshuahamsaverified on: 2026-10-20
degradation_rate
c4 verified · fact
nominal 0.1 PERCENT-PER-YR
Conditions: Extra system degradation that some independent engineers add on top of the module degradation rate to cover mismatch from uneven module aging. It is a modeling allowance, not a universal rule.
verified by: joshuahamsaverified on: 2026-10-20
Referenced by
Data