Important: A "bad month" is not yield shortfall. What matters is a clean classification using weather data, availability and plausible expected values.
What Is Yield Shortfall?
Yield shortfall occurs when a system repeatedly falls below plausible expected values over a relevant period. Expected values can be: yield forecasts, prior-year comparisons, reference systems or model-based expectations (with weather correction).
Typical Causes (the genuinely common ones)
- Shading/soiling: Temporary, seasonal or permanent (trees, structures, leaves).
- String/layout faults: Mismatched string lengths, MPP range, mixed module fields.
- Inverter/MPP tracker: Misconfiguration, failures, derating, temperature issues.
- Degradation/module faults: PID, hotspots, micro-cracks, LID – depending on module type and environment.
- DC/AC losses: Poor connectors, transition resistances, incorrect cable routing.
- Availability: Faults, shutdowns, fuses, grid issues.
What Data Do You Need for an Initial Assessment?
- Yield data (daily/monthly), ideally per inverter/tracker
- Fault/error logs (inverter)
- System data (kWp, orientation/tilt, module/inverter type)
- String plan/layout (if available)
- Information on shading/changes in surroundings
Systematic Approach (saving time and money)
- Plausibility check: Compare weather, availability and time periods.
- Segment: Which inverters/trackers/strings are underperforming?
- Form hypotheses: e.g. shading vs. layout vs. defect.
- On-site check: Visual inspection (cables, connectors, module fields, hotspot indicators).
- Measurement/verification: Targeted electrical testing where data shows anomalies.
- Assessment: Root cause + yield impact + remedial action plan.
When Does It Become Admissible Evidence?
When you not only demonstrate deviations but also explain them technically and document them in a traceable manner. This is relevant for warranty claims, insurance cases and disputes.
FAQ
From what point is there yield shortfall?
When yields repeatedly fall below plausible expected values over a relevant period and weather/availability has been taken into account.
What data is needed for an initial assessment?
Yield data, system data, inverters/strings, location and information on shading/faults.
Can monitoring alone prove the cause?
Monitoring shows deviations but does not always prove the cause. Substantiated findings often require a document review and measurements.
Email: info@gutachterpv.org