PV string underperformance
A string delivering less current than its peers under the same irradiance.
PV string underperformance is when one string produces measurably less current than identical neighbouring strings at the same irradiance and temperature. Typical causes are connector corrosion, partial shading, a failed module, or a tripped bypass diode. Left unaddressed it costs 2–8% of that string’s annual yield.
Symptoms
- One string’s current sits consistently below sibling strings on the same MPPT.
- The gap widens at high irradiance rather than staying proportional.
- Performance ratio for the affected combiner drifts down over weeks.
SCADA signatures
- Per-string current (Istr) 3–15% below the MPPT median during clear-sky midday.
- Stable voltage but depressed current — distinguishes it from a voltage fault.
- No corresponding irradiance or temperature anomaly on the reference sensor.
Root cause
Most often progressive series resistance from corroded MC4 connectors or junction-box solder, a single open-circuited module, or soft partial shading. Because the loss tracks irradiance, it compounds in summer when the asset earns most.
Financial impact
A persistent 5% deficit on a 1 MWp string block in southern Europe is roughly €1,500–3,000/year in lost generation — and the connector fault that caused it can escalate into an arc-fault safety event if ignored.
How NuraVolt detects it
NuraVolt benchmarks each string against its own cohort using a physics-informed expected-current model, so it separates genuine underperformance from irradiance and temperature effects. The rule layer flags the deficit; the RUL layer tracks whether the slope is degrading (connector corrosion) or step-change (module failure).
Frequently asked questions
See also
See this on your own plants
NuraVolt turns your SCADA and BMS data into early fault detection, degradation-aware BESS analytics, and audit-ready reporting. A fixed-scope audit shows you what we’d find on your portfolio.