The module puts out less power at standard test conditions than its nameplate says. This is found by flash testing or IV tracing a stabilised module, and it may also show up in monitoring data. If the module was below tolerance when new, the cause is a non-conforming power rating rather than degradation. Lab measurement uncertainty and the manufacturer's tolerance must be taken into account before calling it non-conforming. Light induced degradation lowers STC power along with Isc and Voc early in the system's life, with no visible defect. In some cases a patchwork pattern in EL images points to it. Delamination lowers Pmax mainly by cutting short-circuit current, because the air gaps reflect more light. It can be seen visually, and pulse thermography or scanning acoustic microscopy can detect it. Corrosion or abrasion of the glass or its anti-reflective coating cuts light transmission. The loss is usually a few percent and levels off over time. Look for it visually, and check reflectance after cleaning. First, compare stabilised flash-test or IV results and early production trends against the nameplate and the losses expected for that module technology. Then have an accredited lab confirm the underperformance before filing a warranty claim.
<!-- review notes
observed_asc1 drafted · lead Pmax below rated value
Flash or IV test of a stabilised module gives STC power below the nameplate minimum after allowing for tolerance and lab uncertainty.
sec=h45 h=2e9980a0b004sec=h67 h=91bca7f04152c2 drafted · lead Lowered Isc on IV curve
With delamination the Pmax loss comes mostly from lower Isc caused by extra reflection; LID also lowers Isc.
sec=2.3.2 h=5147bca98d09sec=h69 h=bdc3ce4bcd6csec=h46 h=1ff4ba1a643ec3 drafted · lead Low open-circuit voltage
LID/LeTID lowers Voc together with STC power.
sec=h69 h=bdc3ce4bcd6csec=h46 h=1ff4ba1a643ec4 drafted · lead Patchwork EL pattern
EL images becoming less uniform can sometimes point to ongoing light-induced degradation.
sec=h69 h=bdc3ce4bcd6csec=h46 h=1ff4ba1a643etypical_power_lossc5 drafted · lead ≤ 30 PERCENT
Conditions: Light induced degradation (light soaking), upper bound reported in one source
sec=h3 h=950db263c013Conditions: Boron-oxygen LID in c-Si modules, occurring within the first days of sun exposure
sec=h69 h=bdc3ce4bcd6csec=h46 h=1ff4ba1a643econflicts with: Reduced STC output power (c9)conflicts with: Reduced STC output power (c11)
Conditions: LeTID in PERC-type modules at temperatures above 50 °C, developing over years and adding to LID loss
sec=h69 h=bdc3ce4bcd6csec=h46 h=1ff4ba1a643econflicts with: Reduced STC output power (c9)conflicts with: Reduced STC output power (c11)
Conditions: LeTID in modules from manufacturers using in-line mitigation; varies by manufacturer
sec=h69 h=bdc3ce4bcd6cconflicts with: Reduced STC output power (c9)conflicts with: Reduced STC output power (c11)
c9 disputed nominal 20 PERCENT
Conditions: Field EFG-Si module with edge delamination and discoloration, first 3 years of deployment (reported as nearly 20% Pmax drop)
sec=2.3.2 h=5147bca98d09review note: possible conflict with c11 (same source; check the conditions)conflicts with: Reduced STC output power (c6)conflicts with: Reduced STC output power (c7)conflicts with: Reduced STC output power (c8)
c11 disputed nominal 11.5 PERCENT
Conditions: PV system after 12 years of exposure, loss attributed mostly to delamination at the cell/encapsulant interface
sec=2.3.2 h=5147bca98d09review note: possible conflict with c9 (same source; check the conditions)conflicts with: Reduced STC output power (c6)conflicts with: Reduced STC output power (c7)conflicts with: Reduced STC output power (c8)
current_dropc10 drafted · lead nominal 5 PERCENT
Conditions: Same field EFG-Si module with delamination, Isc drop over the first 3 years (reported as about 5%)
sec=2.3.2 h=5147bca98d09presents_as c16presents_as c9presents_as c4