Power vs irradiance analysis plots the measured output power of an inverter or plant against the in-plane irradiance measured at the same time, using monitoring data. It is the recommended way to check for inverter overheating. An overheating inverter reduces its power or shuts off to protect itself and does not always report a power reduction or derating message. Inverter power limitation, or clipping, shows up as a flat cap in the curve above a certain irradiance level. The loss from this limitation cannot be measured directly. It can be estimated from measured values by comparing the performance ratio in the low and high irradiance ranges. The same plot also shows outliers in the power-irradiance data, which should be filtered out before further analysis. Monitoring is the main way to detect inverter overheating, with IV curve tracing and infrared thermography as additional checks. The result depends on irradiance sensor quality, so follow the recommended limits on irradiance uncertainty and sensor alignment.
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producesc1 verified · fact Temperature-linked output derating
An overheating inverter cuts its power or shuts off to protect itself, often without reporting a derating status message. Analysing the power vs irradiance curve brings this behaviour to light.
tbl=51.r1 h=52f99f2ab326tbl=33.r1 h=44fc567b4d48verified by: review-workflowverified on: 2026-10-20
c2 drafted · lead Power plateau at high irradiance
Plotting measured AC output against in-plane irradiance shows inverter power limitation (clipping) as a flat cap above a certain specific irradiance level.
sec=4.2.2 h=baaa36bbb1c3fig=52 h=42f871f06665sec=B.2 h=5c54e661da25review note: support check: partial - Passages show inverter power limitation visible above an irradiance level in power vs irradiance plots, but don't explicitly describe a flat constant ceiling.
c3 verified · fact Power-irradiance outlier
A scatter plot of power against plane-of-array irradiance reveals outlier data pairs. These can be removed by statistical filtering.
sec=B.2 h=5c54e661da25sec=h17 h=5714454c65c6verified by: review-workflowverified on: 2026-10-20
typical_power_lossc4 verified · fact nominal 0.05 PERCENT
Conditions: Annual energy loss from inverter power limitation, deduced by PR extrapolation from measured 5-min power vs irradiance data (PR 200-900 W/m² vs 900-1200 W/m²) for one example system
sec=4.2.2 h=baaa36bbb1c3verified by: review-workflowverified on: 2026-10-20review note: possible conflict with c5 (same source; check the conditions)
c5 drafted · lead nominal 0.03 PERCENT
Conditions: Inverter limitation loss predicted by simulation for the same example system at a PV to inverter power ratio of 1.12
sec=4.2.2 h=baaa36bbb1c3review note: possible conflict with c4 (same source; check the conditions)
detected_by c9