When is a PV yield assessment worthwhile?

When the system persistently underperforms relative to forecasts or expected values, when warranty/insurance matters are involved, or when causes need to be substantiated with evidence.

What data is required?

Yield data (ideally daily), inverter/tracker data, fault logs, system parameters (kWp, orientation/tilt), string plan if available, and information on shading or site changes.

How does an expert report differ from monitoring?

Monitoring shows deviations. An expert report explains the cause, quantifies the yield impact and provides substantiated documentation – essential for third parties (e.g. insurer, installer, lawyer).

PV Yield Assessment | Proving Shortfall & Identifying Causes

A PV yield assessment is the right tool when it is no longer about "gut feeling" but about substantiated evidence: quantifying the deviation, technically explaining the cause, calculating the yield impact and prioritising remedial measures. It is the key document that operators, insurers, lawyers and investors need when monitoring figures alone are no longer sufficient.

ObjectiveAssess yield shortfall in an evidentially sound manner

ResultCause + yield impact + recommended actions

ForOperators, insurers, disputes, acquisition review

FocusTechnology, data, measurement, documentation

What Is a PV Yield Assessment?

A PV yield assessment is a technical expert opinion that systematically investigates why a photovoltaic system generates less electricity than expected. Unlike a simple monitoring report that merely shows deviations, a yield assessment provides a causal explanation: which technical, planning or operational factors are causing the yield shortfall? What is the monetary loss? What action must be taken?

The assessment is produced by an independent expert and is structured so that it holds up as evidence in court, with insurers and vis-à-vis the installer. It contains measurement data, references to standards, photo documentation and a traceable root cause analysis.

Common Situations Requiring a Yield Assessment

In practice, there are four frequent situations in which a PV yield assessment becomes necessary:

Persistently below forecast: The system has been generating significantly less than projected for months or years. The operator suspects a technical defect but cannot substantiate it.
Dispute with the installer: The installer declares yields to be "within normal range" while the operator records measurable losses. Without independent documentation, legal proceedings are difficult to win.
Insurance claim / loss settlement: After storm, hail or lightning damage, it must be proven what proportion of the yield loss is attributable to the damage – and what was already missing beforehand.
Purchase or sale of a PV system: Investors and buyers require an independent plausibility check of historical yield data before setting a purchase price.

How a Yield Assessment Works

A structured PV yield assessment follows a three-stage process:

1) Data AnalysisYield data, inverter logs, plausibility checks, comparison with reference sites and irradiation data

2) Narrowing DownWhich inverters, trackers or strings deviate? Form hypotheses, systematically rule out causes

3) On-Site VerificationTechnical inspection and measurements on anomalous components, photo documentation, infrared thermography if required

The result is a written assessment with root cause finding, yield impact calculation and concrete action recommendations. This document serves as a sound basis for negotiations, warranty claims or court proceedings.

In a free initial consultation we will tell you whether a yield assessment makes sense and what it is likely to cost.

Email: info@gutachterpv.org

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